M is single-digit-allowed (1, 2, …, 12). MM is always two digits (01, 02, …, 12). Human-readable formats usually use M; machine formats like ISO 8601 use MM.

Is YYYY the same as yyyy?

It depends on the library. moment.js treats them the same, but ISO 8601's `yyyy` is the 'week year', which can differ from the calendar year by a few days around new year. For most cases stick with YYYY.

How are timezones handled?

Default is the browser's local TZ. If the input contains a TZ offset (`+09:00`), that's honored. Run inputs through the timezone tool first if you need explicit conversion.

Date Formatter

Example

Input (date + pattern)

Date: 2026-05-13T14:30:00
Pattern: dddd, MMM D, YYYY · HH:mm

Output

Wednesday, May 13, 2026 · 14:30

Note

Token cheat sheet — YYYY=4-digit year, M=1+digit month, MM=2-digit, D=day, HH=24h hour, h=12h hour, A=AM/PM, dddd=full weekday, etc.

Usage / FAQ

When to use

Quickly validate format tokens for moment.js, dayjs, date-fns
Produce locale-specific date strings (e.g. Korean style: 2026년 5월 13일 수요일)
Design date formats for emails, invoices, and reports
Translate ISO 8601 into a human-friendly string
Audit date formatting across multi-language sites

FAQ

Q.M vs MM?: A.M is single-digit-allowed (1, 2, …, 12). MM is always two digits (01, 02, …, 12). Human-readable formats usually use M; machine formats like ISO 8601 use MM.
Q.Is YYYY the same as yyyy?: A.It depends on the library. moment.js treats them the same, but ISO 8601's `yyyy` is the 'week year', which can differ from the calendar year by a few days around new year. For most cases stick with YYYY.
Q.How are timezones handled?: A.Default is the browser's local TZ. If the input contains a TZ offset (`+09:00`), that's honored. Run inputs through the timezone tool first if you need explicit conversion.

Fun facts

ISO 8601 (1988) locked in the `YYYY-MM-DD` standard. 'Largest unit first' + always four-digit year + zero-padding — meaning lexical sort equals chronological sort. Before that, US `MM/DD/YYYY` and European `DD/MM/YYYY` clashed and made data exchange a nightmare.
ISO 8601 — Official
The `strftime` format tokens (`%Y` `%m` `%d` `%H` etc.) were baked into ANSI C in 1989. The Unix `date` command and every language since (Python, Ruby, PHP, …) adopted the convention as-is — it's a 30+ year lingua franca.
POSIX strftime
JavaScript's `Date` object uses 0-based units, so months are 0 (January) – 11 (December). That's a fossil from 1995 — Brendan Eich built JavaScript in 10 days, and Java's `java.util.Date` (also 0-based months) was the model. Its side effects have been trapping JS developers for 30 years.
MDN — Date constructor

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Input (date + pattern)

Output

Note

When to use

FAQ

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