getWeekOfMonth

Signature

getWeekOfMonth(value: string, locale: string): number

import { getWeekOfMonth } from "@northguild/gmt/plain/calculate";

Return the 1-based row value falls on within its month’s calendar

• grid, using locale’s first day of week.
• Week 1 is the row containing the 1st of the month, even when that row is a partial week (matches date-fns’s getWeekOfMonth, verified against date-fns source 2026-08-21) — this is the convention every calendar-grid UI (and @internationalized/date’s getWeeksInMonth) expects for sizing a month grid.
• Distinct from ISO weekOfYear: this counts rows within a single month’s grid, reset every month, rather than weeks since Jan 1.
• Resolves the locale’s first day of week via Intl.Locale.prototype.weekInfo.
• Returns null if value or locale is invalid.

Parameters

Parameter	Type	Description
value	string	ISO PlainDate string
locale	string	BCP 47 locale tag (e.g. “en-US”, “fr-FR”)

Returns

1-based week-of-month row, or null on invalid input

Examples

getWeekOfMonth("2024-02-01", "en-US") // 1
getWeekOfMonth("2024-02-29", "en-US") // 5
getWeekOfMonth("2026-02-01", "en-US") // 1
getWeekOfMonth("2026-02-01", "en-GB") // 1
getWeekOfMonth("invalid", "en-US") // null

Source

plain/calculate/getWeekOfMonth.ts