diff --git a/pnpm-lock.yaml b/pnpm-lock.yaml
index 9b8c6fdd7a0c..3d9db9fa76d6 100644
--- a/pnpm-lock.yaml
+++ b/pnpm-lock.yaml
@@ -3866,6 +3866,9 @@ importers:
 
   projects/packages/premium-analytics:
     dependencies:
+      '@date-fns/tz':
+        specifier: 1.4.1
+        version: 1.4.1
       '@wordpress/boot':
         specifier: 0.13.0
         version: 0.13.0(react-dom@18.3.1(react@18.3.1))(react@18.3.1)
@@ -3881,6 +3884,9 @@ importers:
       '@wordpress/route':
         specifier: 0.12.0
         version: 0.12.0(react-dom@18.3.1(react@18.3.1))(react@18.3.1)
+      date-fns:
+        specifier: 4.1.0
+        version: 4.1.0
       react:
         specifier: 18.3.1
         version: 18.3.1
diff --git a/projects/packages/premium-analytics/changelog/wooa7s-1312-integrate-datetime-package-into-analytics b/projects/packages/premium-analytics/changelog/wooa7s-1312-integrate-datetime-package-into-analytics
new file mode 100644
index 000000000000..56b6c3ea2da2
--- /dev/null
+++ b/projects/packages/premium-analytics/changelog/wooa7s-1312-integrate-datetime-package-into-analytics
@@ -0,0 +1,4 @@
+Significance: patch
+Type: added
+
+Port datetime package (timezone-aware date helpers and date-range presets) as an internal package from next-woocommerce-analytics.
diff --git a/projects/packages/premium-analytics/eslint.config.mjs b/projects/packages/premium-analytics/eslint.config.mjs
new file mode 100644
index 000000000000..4d905c2efea4
--- /dev/null
+++ b/projects/packages/premium-analytics/eslint.config.mjs
@@ -0,0 +1,16 @@
+import { makeBaseConfig, defineConfig } from 'jetpack-js-tools/eslintrc/base.mjs';
+
+/**
+ * Soften JSDoc rules for `packages/datetime/**` so the initial port can
+ * land. Temporary — backfill proper descriptions on the helpers and
+ * remove this override (at which point this whole file can go away).
+ */
+export default defineConfig( makeBaseConfig( import.meta.url ), {
+	files: [ 'packages/datetime/**' ],
+	rules: {
+		'jsdoc/require-description': 'off',
+		'jsdoc/require-param-description': 'off',
+		'jsdoc/require-returns': 'off',
+		'jsdoc/check-indentation': 'off',
+	},
+} );
diff --git a/projects/packages/premium-analytics/package.json b/projects/packages/premium-analytics/package.json
index 31d5de969868..3f0ab771f18b 100644
--- a/projects/packages/premium-analytics/package.json
+++ b/projects/packages/premium-analytics/package.json
@@ -29,11 +29,13 @@
 		}
 	},
 	"dependencies": {
+		"@date-fns/tz": "1.4.1",
 		"@wordpress/boot": "0.13.0",
 		"@wordpress/data": "10.46.0",
 		"@wordpress/i18n": "^6.9.0",
 		"@wordpress/icons": "^13.0.0",
 		"@wordpress/route": "0.12.0",
+		"date-fns": "4.1.0",
 		"react": "18.3.1",
 		"react-dom": "18.3.1"
 	},
diff --git a/projects/packages/premium-analytics/packages/datetime/README.md b/projects/packages/premium-analytics/packages/datetime/README.md
new file mode 100644
index 000000000000..ce284079bfee
--- /dev/null
+++ b/projects/packages/premium-analytics/packages/datetime/README.md
@@ -0,0 +1,129 @@
+# @automattic/jetpack-premium-analytics-datetime
+
+Date and timezone utilities for Jetpack Premium Analytics.
+
+## Overview
+
+Provides timezone-aware date handling and comparison range calculations
+for analytics widgets and date-range pickers.
+
+## Functions
+
+### Timezone Utilities
+
+#### `createTZDateFromParts( dateParts: number[], timezone? )`
+
+Creates a timezone-aware date in the specified timezone using the provided date parts.
+**Important:** Months are zero-based (0 = January, 11 = December).
+
+```ts
+// October 09, 2025 00:00 AM in America/New_York time
+const date = createTZDateFromParts( [ 2025, 9, 9 ], 'America/New_York' );
+```
+
+**Parameters:**
+
+- `dateParts` : `number[]` - Date value to convert
+- `timezone` (optional): `string` - Target timezone, default is GMT
+
+**Returns:** `TZDate` - Timezone-aware date object
+
+#### `toLocalTZ( value?, timezone? )`
+
+Creates a timezone-aware date in the specified timezone.
+
+```typescript
+const date = toLocalTZ( '2024-01-15', 'America/New_York' );
+const now = toLocalTZ( undefined, '+05:30' ); // Current time in +05:30
+```
+
+**Parameters:**
+
+- `value` (optional): `number | string | Date` - Date value to convert
+- `timezone` (optional): `string` - Target timezone
+
+**Returns:** `TZDate` - Timezone-aware date object
+
+#### `formatToTimezoneNaiveString( date, timezone )`
+
+Formats a date to an ISO string without timezone offset.
+
+```typescript
+const naive = formatToTimezoneNaiveString( new Date(), 'Europe/London' );
+// Returns: "2024-01-15T14:30:00.000"
+```
+
+**Parameters:**
+
+- `date`: `Date` - Date to format
+- `timezone`: `string` - Timezone for interpretation
+
+**Returns:** `string` - ISO string without timezone offset
+
+#### `dateToISOStringWithTZ( date, timezone )`
+
+Converts a date to ISO string with timezone offset applied.
+
+```typescript
+const withTZ = dateToISOStringWithTZ( new Date(), 'America/New_York' );
+// Returns: "2024-01-15T14:30:00.000-05:00"
+```
+
+**Parameters:**
+
+- `date`: `Date` - Date to convert
+- `timezone`: `string` - Target timezone
+
+**Returns:** `string` - ISO string with timezone offset
+
+### Comparison Range Calculations
+
+#### `getComparisonRangeFromPreset( reference, presetId )`
+
+Calculates comparison date ranges based on predefined presets.
+
+```typescript
+const reference = {
+	from: new Date( '2024-01-15' ),
+	to: new Date( '2024-01-21' ),
+};
+const comparison = getComparisonRangeFromPreset( reference, 'previous-week' );
+// Returns dates for Jan 8-14, 2024
+```
+
+**Parameters:**
+
+- `reference`: `DateRange` - Reference date range with `from` and `to`
+- `presetId`: `ComparisonPresetId` - One of the supported preset identifiers
+
+**Returns:** `DateRange | undefined` - Comparison date range or undefined
+if inputs are invalid
+
+**Supported presets:**
+
+- `previous-period` - Same duration, immediately before reference
+- `previous-week` - One week before reference dates
+- `previous-month` - One month before reference dates
+- `previous-year` - One year before reference dates
+
+## Types
+
+### `DateRange`
+
+```typescript
+type DateRange = {
+	from?: Date;
+	to?: Date;
+};
+```
+
+### `ComparisonPresetId`
+
+```typescript
+type ComparisonPresetId = 'previous-period' | 'previous-week' | 'previous-month' | 'previous-year';
+```
+
+## Dependencies
+
+- `date-fns` - Date manipulation functions
+- `@date-fns/tz` - Timezone support for date-fns
diff --git a/projects/packages/premium-analytics/packages/datetime/package.json b/projects/packages/premium-analytics/packages/datetime/package.json
new file mode 100644
index 000000000000..b4a9dfcea148
--- /dev/null
+++ b/projects/packages/premium-analytics/packages/datetime/package.json
@@ -0,0 +1,14 @@
+{
+	"name": "@automattic/jetpack-premium-analytics-datetime",
+	"version": "0.1.0",
+	"private": true,
+	"type": "module",
+	"main": "src/index.ts",
+	"types": "src/index.ts",
+	"sideEffects": false,
+	"dependencies": {
+		"@date-fns/tz": "1.4.1",
+		"@wordpress/i18n": "^6.9.0",
+		"date-fns": "4.1.0"
+	}
+}
diff --git a/projects/packages/premium-analytics/packages/datetime/src/get-comparison-range.ts b/projects/packages/premium-analytics/packages/datetime/src/get-comparison-range.ts
new file mode 100644
index 000000000000..5c04d56f6323
--- /dev/null
+++ b/projects/packages/premium-analytics/packages/datetime/src/get-comparison-range.ts
@@ -0,0 +1,105 @@
+/**
+ * External dependencies
+ */
+import {
+	differenceInDays,
+	subDays,
+	subWeeks,
+	subMonths,
+	subYears,
+	startOfDay,
+	endOfDay,
+} from 'date-fns';
+
+/**
+ * Supported comparison preset identifiers.
+ */
+export type DateRange = { from?: Date; to?: Date };
+
+/**
+ * Named constants for comparison preset identifiers.
+ */
+export const COMPARISON_PREVIOUS_PERIOD = 'previous-period' as const;
+export const COMPARISON_PREVIOUS_WEEK = 'previous-week' as const;
+export const COMPARISON_PREVIOUS_MONTH = 'previous-month' as const;
+export const COMPARISON_PREVIOUS_YEAR = 'previous-year' as const;
+
+/**
+ * All comparison preset identifiers, in display order.
+ */
+export const COMPARISON_PRESETS = [
+	COMPARISON_PREVIOUS_PERIOD,
+	COMPARISON_PREVIOUS_WEEK,
+	COMPARISON_PREVIOUS_MONTH,
+	COMPARISON_PREVIOUS_YEAR,
+] as const;
+
+export type ComparisonPresetId = ( typeof COMPARISON_PRESETS )[ number ];
+
+/**
+ * Type guard to check if a string is a valid ComparisonPresetId.
+ *
+ * @param value - The value to check.
+ * @return True if the value is a valid ComparisonPresetId, false otherwise.
+ */
+export function isComparisonPresetId( value: unknown ): value is ComparisonPresetId {
+	return typeof value === 'string' && ( COMPARISON_PRESETS as readonly string[] ).includes( value );
+}
+
+/**
+ * Returns a comparison DateRange (as Date objects) derived from a reference range
+ * and a given preset.
+ *
+ * - This function is pure and has no side effects.
+ * - It does not apply any timezone adjustments. The caller is responsible for
+ *   normalizing dates to the desired local day boundaries before passing them in.
+ *
+ * @param reference - The reference range to compare against (must include both `from` and `to`).
+ * @param presetId  - One of the supported preset identifiers.
+ * @return A new DateRange for the comparison period, or `undefined` if inputs are invalid.
+ */
+export function getComparisonRangeFromPreset(
+	reference: DateRange,
+	presetId: ComparisonPresetId
+): DateRange | undefined {
+	if ( ! reference?.from || ! reference?.to ) {
+		return undefined;
+	}
+
+	const refFrom = reference.from;
+	const refTo = reference.to;
+
+	const clampDayBound = ( date: Date, bound: 0 | 1 ) =>
+		bound === 1 ? endOfDay( startOfDay( date ) ) : startOfDay( date );
+
+	if ( presetId === COMPARISON_PREVIOUS_PERIOD ) {
+		const daysInclusive = differenceInDays( refTo, refFrom ) + 1;
+		return {
+			from: clampDayBound( subDays( refFrom, daysInclusive ), 0 ),
+			to: clampDayBound( subDays( refTo, daysInclusive ), 1 ),
+		};
+	}
+
+	if ( presetId === COMPARISON_PREVIOUS_WEEK ) {
+		return {
+			from: clampDayBound( subWeeks( refFrom, 1 ), 0 ),
+			to: clampDayBound( subWeeks( refTo, 1 ), 1 ),
+		};
+	}
+
+	if ( presetId === COMPARISON_PREVIOUS_MONTH ) {
+		return {
+			from: clampDayBound( subMonths( refFrom, 1 ), 0 ),
+			to: clampDayBound( subMonths( refTo, 1 ), 1 ),
+		};
+	}
+
+	if ( presetId === COMPARISON_PREVIOUS_YEAR ) {
+		return {
+			from: clampDayBound( subYears( refFrom, 1 ), 0 ),
+			to: clampDayBound( subYears( refTo, 1 ), 1 ),
+		};
+	}
+
+	return undefined;
+}
diff --git a/projects/packages/premium-analytics/packages/datetime/src/index.ts b/projects/packages/premium-analytics/packages/datetime/src/index.ts
new file mode 100644
index 000000000000..fd8f8ac3e8ff
--- /dev/null
+++ b/projects/packages/premium-analytics/packages/datetime/src/index.ts
@@ -0,0 +1,49 @@
+export {
+	getComparisonRangeFromPreset,
+	isComparisonPresetId,
+	type DateRange,
+	type ComparisonPresetId,
+} from './get-comparison-range';
+
+export {
+	createTZDateFromParts,
+	toLocalTZ,
+	formatToTimezoneNaiveString,
+	dateToISOStringWithTZ,
+	startOfDayTZ,
+	endOfDayTZ,
+} from './tz';
+
+export {
+	// Constants
+	SELECTABLE_PRESETS,
+	PRESET_TODAY,
+	PRESET_YESTERDAY,
+	PRESET_LAST_7_DAYS,
+	PRESET_LAST_30_DAYS,
+	PRESET_LAST_90_DAYS,
+	PRESET_LAST_365_DAYS,
+	PRESET_LAST_MONTH,
+	PRESET_LAST_12_MONTHS,
+	PRESET_LAST_YEAR,
+	PRESET_CUSTOM,
+
+	// Guards
+	isSelectablePreset,
+	isPrimaryPreset,
+
+	// Types
+	type SelectablePresetId,
+	type PrimaryPresetId,
+
+	// Primary presets
+	PRESET_DEFINITIONS,
+	getPresetLabel,
+	getDefaultDateRangePresets,
+	computePrimaryRange,
+	type DateRangePreset,
+
+	// Comparison presets
+	getComparisonPresetLabel,
+	getComparisonPresetConfigs,
+} from './presets';
diff --git a/projects/packages/premium-analytics/packages/datetime/src/presets/comparison.ts b/projects/packages/premium-analytics/packages/datetime/src/presets/comparison.ts
new file mode 100644
index 000000000000..b993189947fc
--- /dev/null
+++ b/projects/packages/premium-analytics/packages/datetime/src/presets/comparison.ts
@@ -0,0 +1,65 @@
+/**
+ * External dependencies
+ */
+import { __ } from '@wordpress/i18n';
+/**
+ * Internal dependencies
+ */
+import {
+	COMPARISON_PREVIOUS_PERIOD,
+	COMPARISON_PREVIOUS_WEEK,
+	COMPARISON_PREVIOUS_MONTH,
+	COMPARISON_PREVIOUS_YEAR,
+	type ComparisonPresetId,
+} from '../get-comparison-range';
+
+/**
+ * Comparison preset label configuration.
+ */
+const COMPARISON_PRESET_LABELS: {
+	id: ComparisonPresetId;
+	getLabel: () => string;
+}[] = [
+	{
+		id: COMPARISON_PREVIOUS_PERIOD,
+		getLabel: () => __( 'Previous period', 'jetpack-premium-analytics' ),
+	},
+	{
+		id: COMPARISON_PREVIOUS_WEEK,
+		getLabel: () => __( 'Previous week', 'jetpack-premium-analytics' ),
+	},
+	{
+		id: COMPARISON_PREVIOUS_MONTH,
+		getLabel: () => __( 'Previous month', 'jetpack-premium-analytics' ),
+	},
+	{
+		id: COMPARISON_PREVIOUS_YEAR,
+		getLabel: () => __( 'Previous year', 'jetpack-premium-analytics' ),
+	},
+];
+
+/**
+ * Get the label for a comparison preset.
+ *
+ * @param id - The comparison preset identifier.
+ * @return The label string, or null if not found.
+ */
+export function getComparisonPresetLabel( id: ComparisonPresetId ): string | null {
+	const config = COMPARISON_PRESET_LABELS.find( item => item.id === id );
+	return config?.getLabel() ?? null;
+}
+
+/**
+ * Get all comparison preset configurations (id + label).
+ *
+ * @return Array of comparison preset configs.
+ */
+export function getComparisonPresetConfigs(): {
+	id: ComparisonPresetId;
+	label: string;
+}[] {
+	return COMPARISON_PRESET_LABELS.map( ( { id, getLabel } ) => ( {
+		id,
+		label: getLabel(),
+	} ) );
+}
diff --git a/projects/packages/premium-analytics/packages/datetime/src/presets/index.ts b/projects/packages/premium-analytics/packages/datetime/src/presets/index.ts
new file mode 100644
index 000000000000..d3e4f17ca93b
--- /dev/null
+++ b/projects/packages/premium-analytics/packages/datetime/src/presets/index.ts
@@ -0,0 +1,27 @@
+export {
+	SELECTABLE_PRESETS,
+	PRESET_TODAY,
+	PRESET_YESTERDAY,
+	PRESET_LAST_7_DAYS,
+	PRESET_LAST_30_DAYS,
+	PRESET_LAST_90_DAYS,
+	PRESET_LAST_365_DAYS,
+	PRESET_LAST_MONTH,
+	PRESET_LAST_12_MONTHS,
+	PRESET_LAST_YEAR,
+	PRESET_CUSTOM,
+	isSelectablePreset,
+	isPrimaryPreset,
+	type SelectablePresetId,
+	type PrimaryPresetId,
+} from './types';
+
+export {
+	PRESET_DEFINITIONS,
+	getPresetLabel,
+	getDefaultDateRangePresets,
+	computePrimaryRange,
+	type DateRangePreset,
+} from './primary';
+
+export { getComparisonPresetLabel, getComparisonPresetConfigs } from './comparison';
diff --git a/projects/packages/premium-analytics/packages/datetime/src/presets/primary.ts b/projects/packages/premium-analytics/packages/datetime/src/presets/primary.ts
new file mode 100644
index 000000000000..8807338f6712
--- /dev/null
+++ b/projects/packages/premium-analytics/packages/datetime/src/presets/primary.ts
@@ -0,0 +1,220 @@
+/**
+ * External dependencies
+ */
+import { __ } from '@wordpress/i18n';
+import {
+	startOfDay,
+	endOfDay,
+	subDays,
+	subMonths,
+	subYears,
+	startOfMonth,
+	endOfMonth,
+	startOfYear,
+	endOfYear,
+} from 'date-fns';
+/**
+ * Internal dependencies
+ */
+import { toLocalTZ } from '../tz';
+import {
+	PRESET_TODAY,
+	PRESET_YESTERDAY,
+	PRESET_LAST_7_DAYS,
+	PRESET_LAST_30_DAYS,
+	PRESET_LAST_90_DAYS,
+	PRESET_LAST_365_DAYS,
+	PRESET_LAST_MONTH,
+	PRESET_LAST_12_MONTHS,
+	PRESET_LAST_YEAR,
+	PRESET_CUSTOM,
+	type SelectablePresetId,
+	type PrimaryPresetId,
+} from './types';
+import type { DateRange } from '../get-comparison-range';
+
+/**
+ * Shared date calculations used by multiple presets.
+ */
+type DateContext = {
+	initOfToday: Date;
+	endOfToday: Date;
+	endOfYesterday: Date;
+	lastMonth: Date;
+	endOfLastMonth: Date;
+	lastYear: Date;
+};
+
+/**
+ * Preset definition with label getter and range calculator.
+ */
+type PresetDefinition = {
+	id: SelectablePresetId;
+	getLabel: () => string;
+	getRange: ( ctx: DateContext ) => Required< DateRange >;
+};
+
+/**
+ * Canonical preset definitions with labels and range calculators.
+ * Labels are defined once here and reused by all consumers.
+ */
+export const PRESET_DEFINITIONS: ReadonlyArray< PresetDefinition > = [
+	{
+		id: PRESET_TODAY,
+		getLabel: () => __( 'Today', 'jetpack-premium-analytics' ),
+		getRange: ( { initOfToday, endOfToday } ) => ( {
+			from: initOfToday,
+			to: endOfToday,
+		} ),
+	},
+	{
+		id: PRESET_YESTERDAY,
+		getLabel: () => __( 'Yesterday', 'jetpack-premium-analytics' ),
+		getRange: ( { initOfToday, endOfYesterday } ) => ( {
+			from: subDays( initOfToday, 1 ),
+			to: endOfYesterday,
+		} ),
+	},
+	{
+		id: PRESET_LAST_7_DAYS,
+		getLabel: () => __( 'Last 7 days', 'jetpack-premium-analytics' ),
+		getRange: ( { initOfToday, endOfYesterday } ) => ( {
+			from: subDays( initOfToday, 7 ),
+			to: endOfYesterday,
+		} ),
+	},
+	{
+		id: PRESET_LAST_30_DAYS,
+		getLabel: () => __( 'Last 30 days', 'jetpack-premium-analytics' ),
+		getRange: ( { initOfToday, endOfYesterday } ) => ( {
+			from: subDays( initOfToday, 30 ),
+			to: endOfYesterday,
+		} ),
+	},
+	{
+		id: PRESET_LAST_90_DAYS,
+		getLabel: () => __( 'Last 90 days', 'jetpack-premium-analytics' ),
+		getRange: ( { initOfToday, endOfYesterday } ) => ( {
+			from: subDays( initOfToday, 90 ),
+			to: endOfYesterday,
+		} ),
+	},
+	{
+		id: PRESET_LAST_365_DAYS,
+		getLabel: () => __( 'Last 365 days', 'jetpack-premium-analytics' ),
+		getRange: ( { initOfToday, endOfYesterday } ) => ( {
+			from: subDays( initOfToday, 365 ),
+			to: endOfYesterday,
+		} ),
+	},
+	{
+		id: PRESET_LAST_MONTH,
+		getLabel: () => __( 'Last month', 'jetpack-premium-analytics' ),
+		getRange: ( { lastMonth, endOfLastMonth } ) => ( {
+			from: startOfMonth( lastMonth ),
+			to: endOfLastMonth,
+		} ),
+	},
+	{
+		id: PRESET_LAST_12_MONTHS,
+		getLabel: () => __( 'Last 12 months', 'jetpack-premium-analytics' ),
+		getRange: ( { initOfToday, endOfLastMonth } ) => ( {
+			from: startOfMonth( subMonths( initOfToday, 12 ) ),
+			to: endOfLastMonth,
+		} ),
+	},
+	{
+		id: PRESET_LAST_YEAR,
+		getLabel: () => __( 'Last year', 'jetpack-premium-analytics' ),
+		getRange: ( { lastYear } ) => ( {
+			from: startOfYear( lastYear ),
+			to: endOfYear( lastYear ),
+		} ),
+	},
+];
+
+/**
+ * Get the label for a preset without calculating date ranges.
+ *
+ * @param id - The preset identifier
+ * @return The preset label, or null if not found or custom
+ */
+export function getPresetLabel( id: PrimaryPresetId | null | undefined ): string | null {
+	if ( ! id || id === PRESET_CUSTOM ) {
+		return null;
+	}
+
+	const preset = PRESET_DEFINITIONS.find( p => p.id === id );
+	return preset?.getLabel() ?? null;
+}
+
+/**
+ * Build a DateContext for a given timezone.
+ * @param timeZone
+ */
+function buildDateContext( timeZone: string ): DateContext {
+	const nowWithTZ = toLocalTZ( undefined, timeZone );
+	const initOfToday = startOfDay( nowWithTZ );
+	const endOfToday = endOfDay( nowWithTZ );
+	const endOfYesterday = endOfDay( subDays( initOfToday, 1 ) );
+	const lastMonth = subMonths( initOfToday, 1 );
+	const endOfLastMonth = endOfMonth( lastMonth );
+	const lastYear = subYears( initOfToday, 1 );
+
+	return {
+		initOfToday,
+		endOfToday,
+		endOfYesterday,
+		lastMonth,
+		endOfLastMonth,
+		lastYear,
+	};
+}
+
+/**
+ * Represents a date range preset option.
+ * Preset ranges always have both `from` and `to` defined.
+ */
+export type DateRangePreset = {
+	id: PrimaryPresetId;
+	label: string;
+	range: Required< DateRange >;
+};
+
+/**
+ * Get the default date range presets with computed ranges.
+ *
+ * @param timeZone - IANA timezone string (e.g., 'America/New_York')
+ * @return The default date range presets.
+ */
+export function getDefaultDateRangePresets( timeZone: string ): DateRangePreset[] {
+	const ctx = buildDateContext( timeZone );
+
+	return PRESET_DEFINITIONS.map( ( { id, getLabel, getRange } ) => ( {
+		id,
+		label: getLabel(),
+		range: getRange( ctx ),
+	} ) );
+}
+
+/**
+ * Compute the absolute date range (as Date objects) for a given
+ * selectable preset ID in the specified timezone.
+ *
+ * @param presetId - A valid selectable preset identifier.
+ * @param timeZone - IANA timezone string.
+ * @return The computed { from, to } Date range, or undefined
+ *         if the preset is not recognized.
+ */
+export function computePrimaryRange(
+	presetId: SelectablePresetId,
+	timeZone: string
+): DateRange | undefined {
+	const def = PRESET_DEFINITIONS.find( p => p.id === presetId );
+	if ( ! def ) {
+		return undefined;
+	}
+
+	const ctx = buildDateContext( timeZone );
+	return def.getRange( ctx );
+}
diff --git a/projects/packages/premium-analytics/packages/datetime/src/presets/types.ts b/projects/packages/premium-analytics/packages/datetime/src/presets/types.ts
new file mode 100644
index 000000000000..03023e6f677c
--- /dev/null
+++ b/projects/packages/premium-analytics/packages/datetime/src/presets/types.ts
@@ -0,0 +1,63 @@
+/**
+ * Named constants for selectable date-range presets.
+ */
+export const PRESET_TODAY = 'today' as const;
+export const PRESET_YESTERDAY = 'yesterday' as const;
+export const PRESET_LAST_7_DAYS = 'last-7-days' as const;
+export const PRESET_LAST_30_DAYS = 'last-30-days' as const;
+export const PRESET_LAST_90_DAYS = 'last-90-days' as const;
+export const PRESET_LAST_365_DAYS = 'last-365-days' as const;
+export const PRESET_LAST_MONTH = 'last-month' as const;
+export const PRESET_LAST_12_MONTHS = 'last-12-months' as const;
+export const PRESET_LAST_YEAR = 'last-year' as const;
+
+/**
+ * All selectable (non-custom) preset IDs, in display order.
+ */
+export const SELECTABLE_PRESETS = [
+	PRESET_TODAY,
+	PRESET_YESTERDAY,
+	PRESET_LAST_7_DAYS,
+	PRESET_LAST_30_DAYS,
+	PRESET_LAST_90_DAYS,
+	PRESET_LAST_365_DAYS,
+	PRESET_LAST_MONTH,
+	PRESET_LAST_12_MONTHS,
+	PRESET_LAST_YEAR,
+] as const;
+
+/**
+ * Union of the 9 selectable preset identifiers.
+ */
+export type SelectablePresetId = ( typeof SELECTABLE_PRESETS )[ number ];
+
+/**
+ * The custom marker — not user-selectable, used as a disabled state.
+ */
+export const PRESET_CUSTOM = 'custom' as const;
+
+/**
+ * Primary preset: one of the 9 selectable presets, or 'custom'.
+ */
+export type PrimaryPresetId = SelectablePresetId | typeof PRESET_CUSTOM;
+
+/**
+ * Type guard to check if a value is a selectable preset ID.
+ *
+ * @param value - The value to check.
+ * @return True if the value is a valid SelectablePresetId.
+ */
+export function isSelectablePreset( value: unknown ): value is SelectablePresetId {
+	return typeof value === 'string' && ( SELECTABLE_PRESETS as readonly string[] ).includes( value );
+}
+
+/**
+ * Type guard to check if a value is any primary preset ID
+ * (selectable or custom).
+ *
+ * @param value - The value to check.
+ * @return True if the value is a valid PrimaryPresetId.
+ */
+export function isPrimaryPreset( value: unknown ): value is PrimaryPresetId {
+	return isSelectablePreset( value ) || value === PRESET_CUSTOM;
+}
diff --git a/projects/packages/premium-analytics/packages/datetime/src/tz.ts b/projects/packages/premium-analytics/packages/datetime/src/tz.ts
new file mode 100644
index 000000000000..fae1a696e4e4
--- /dev/null
+++ b/projects/packages/premium-analytics/packages/datetime/src/tz.ts
@@ -0,0 +1,129 @@
+/**
+ * External dependencies
+ */
+import { tz, TZDate, TZDateMini } from '@date-fns/tz';
+import { format, isValid, startOfDay, endOfDay } from 'date-fns';
+
+type GrowTuple< T extends unknown[], Max extends number > = T[ 'length' ] extends Max
+	? T
+	: T | GrowTuple< [ ...T, number ], Max >;
+/**
+ * Date parts tuple in the same order as the native `Date` constructor:
+ * [ year, month, day, hours, minutes, seconds, milliseconds ]
+ *
+ * Positions:
+ * - year: full year, e.g. 2025
+ * - month: month index 0–11 (0=January, 11=December)
+ * - day: day of month 1–31 (default 1 if omitted)
+ * - hours: 0–23 (default 0)
+ * - minutes: 0–59 (default 0)
+ * - seconds: 0–59 (default 0)
+ * - milliseconds: 0–999 (default 0)
+ *
+ * Rules:
+ * - Valid lengths: 2 to 7 elements (must always start with [year, month]).
+ * - Do not skip intermediate positions: contiguous prefixes only (trimmed at the first `undefined`).
+ * - Time zone is applied when creating the date (see `createTZDateFromParts`).
+ *
+ * Examples:
+ * - [ 2025, 0 ] → 2025-01-01T00:00:00.000 (January is 0)
+ * - [ 2025, 6, 15, 14, 30 ] → 2025-07-15T14:30:00.000
+ */
+type DateParts = GrowTuple< [ number, number ], 7 >;
+
+/**
+ *
+ * @param root0
+ * @param root0."0"
+ * @param root0."1"
+ * @param root0."2"
+ * @param root0."3"
+ * @param root0."4"
+ * @param root0."5"
+ * @param root0."6"
+ * @param timeZone
+ */
+export function createTZDateFromParts(
+	[ year, month, day, hours, minutes, seconds, milliseconds ]: DateParts,
+	timeZone?: string
+): TZDate {
+	const tzid = timeZone ?? '+00:00';
+
+	const dateParts = [ year, month, day, hours, minutes, seconds, milliseconds ];
+
+	// Trim until first undefined, to match one of the DateParts types.
+	const idx = dateParts.indexOf( undefined );
+	const datePartsTrimmed = idx === -1 ? dateParts : dateParts.slice( 0, idx );
+
+	// @ts-expect-error: We know datePartsTrimmed is a tuple of numbers, spreading is safe.
+	return new TZDateMini( ...datePartsTrimmed, tzid );
+}
+
+/**
+ * Create a TZDate in the provided timezone.
+ * Defaults to UTC when no timezone is given.
+ * @param value
+ * @param timeZone
+ */
+export function toLocalTZ( value?: number | string | Date, timeZone?: string ): TZDate {
+	const tzid = timeZone ?? '+00:00';
+	if ( value !== undefined ) {
+		return new TZDateMini( value as number, tzid );
+	}
+
+	return TZDateMini.tz( tzid );
+}
+
+/**
+ * Format a date to a timezone-naive ISO string (no offset),
+ * using the given timezone for interpretation.
+ * Example: TZDateMini("...+01:00") -> "YYYY-MM-DDTHH:mm:ss.SSS"
+ * @param date
+ * @param timezone
+ */
+export function formatToTimezoneNaiveString( date: Date, timezone: string ): string {
+	if ( ! isValid( date ) ) {
+		throw new Error( 'Invalid date provided' );
+	}
+	return format( date, "yyyy-MM-dd'T'HH:mm:ss.SSS", { in: tz( timezone ) } );
+}
+
+/**
+ * Convert a date to ISO string with the timezone offset applied.
+ * Example output: "YYYY-MM-DDTHH:mm:ss.SSS±hh:mm"
+ * @param date
+ * @param timezone
+ */
+export function dateToISOStringWithTZ( date: Date, timezone: string ): string {
+	return format( date, "yyyy-MM-dd'T'HH:mm:ss.SSSxxx", {
+		in: tz( timezone ),
+	} );
+}
+
+/**
+ * Returns the start of day (00:00:00) for the given date in the specified timezone.
+ *
+ * @param date     - The date to get the start of day for
+ * @param timeZone - Timezone string (e.g., 'America/New_York', 'UTC', '+08:00')
+ * @return A Date object representing midnight in the specified timezone
+ */
+export function startOfDayTZ( date: Date | number, timeZone: string ): Date {
+	// Create TZDate in the target timezone - this interprets the input date in that timezone
+	const tzDate = new TZDateMini( new Date( date ).getTime(), timeZone );
+	// startOfDay from date-fns respects the timezone context in TZDate
+	return startOfDay( tzDate );
+}
+
+/**
+ * Returns the end of day (23:59:59.999) for the given date in the specified timezone.
+ *
+ * @param date     - The date to get the end of day for
+ * @param timeZone - Timezone string (e.g., 'America/New_York', 'UTC', '+08:00')
+ * @return A Date object representing the last millisecond of the day in the specified timezone
+ */
+export function endOfDayTZ( date: Date | number, timeZone: string ): Date {
+	// Create TZDate in the target timezone - this interprets the input date in that timezone
+	const tzDate = new TZDateMini( new Date( date ).getTime(), timeZone );
+	// endOfDay from date-fns respects the timezone context in TZDate
+	return endOfDay( tzDate );
+}