Weekday Finder
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.
| 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##`.
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