Why are weekdays computed in UTC?

A date like `2026-06-04` is ambiguous without a timezone. We treat it as midnight UTC, which gives a consistent weekday regardless of the user's local timezone. If you want the weekday in a specific timezone, append the time and offset (e.g. `2026-06-04T00:00+09:00`).

ISO 8601 weeks always start on Monday, and week 1 of a year is the one containing the first Thursday. So January 1 may belong to the previous year's week 52 or 53. Format: `YYYY-W##`.

Weekday Finder

Time

Find out what weekday a date falls on (or fell on) in any of 12 locales — useful for planning meetings across cultures, looking up historical events, or scheduling recurring tasks. The tool accepts one date per line in `YYYY-MM-DD` format (or anything `Date()` recognizes) and returns the weekday name, day-of-year (1-366), ISO 8601 week number (`2026-W23`), and whether the year is a leap year. All dates are treated as UTC to avoid off-by-one weekday surprises from local timezone shifts.

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Locale

Dates (one per line)

Results

Date (UTC)	Weekday	Day of year	ISO week	Leap year
1969-07-20	Sunday	201	1969-W29	No
2000-01-01	Saturday	1	1999-W52	Yes
2026-06-04	Thursday	155	2026-W23	No
2038-01-19	Tuesday	19	2038-W03	No
2099-12-31	Thursday	365	2099-W53	No

Dates are treated as UTC. Use ISO 8601 (YYYY-MM-DD) for unambiguous parsing.

How to use

Paste or type one date per line (`2026-06-04`, `Jul 20 1969`, `2000-01-01` — anything Date() can parse).
Pick a locale to control how the weekday name is rendered (e.g. 월요일 vs 月曜日 vs Monday vs Lunes).
Copy the tab-separated table for spreadsheets, or use 'Today' to append today's date.

Frequently asked questions

Why are weekdays computed in UTC?: A date like `2026-06-04` is ambiguous without a timezone. We treat it as midnight UTC, which gives a consistent weekday regardless of the user's local timezone. If you want the weekday in a specific timezone, append the time and offset (e.g. `2026-06-04T00:00+09:00`).
What's an ISO week?: ISO 8601 weeks always start on Monday, and week 1 of a year is the one containing the first Thursday. So January 1 may belong to the previous year's week 52 or 53. Format: `YYYY-W##`.