Week Numbers for 2025 — ISO Week List

Week numbers for 2025

2025 has 52 ISO weeks. Week 1 starts on Dec 30, 2024 and week 52 ends on Dec 28, 2025. Each week below shows its ISO week number, the Monday start date, the Sunday end date, and the Unix epoch timestamp for the start of the week (00:00 UTC on Monday). Weeks are numbered per ISO 8601, where week 1 is the week containing the first Thursday of the year and every week runs Monday to Sunday.

Epoch columns are UTC: "Start" is 00:00:00 on the Monday, "End" is 00:00:00 on the Sunday — the first second of the last day, not the last second of the week. For week 1 of 2025, that end value is 1736035200; add 604,799 to any start epoch to land on the week's final second (Sunday 23:59:59).

How to read this table

• Week # — the ISO 8601 week number for that week.
• ISO year — the ISO week-numbering year this week belongs to (can differ from the calendar year for a few edge days).
• Monday start — the date of the Monday that starts the week, in UTC.
• Sunday end — the date of the Sunday that ends the week, in UTC.
• Start epoch (UTC) — Unix timestamp for 00:00 UTC on Monday.
• End epoch (UTC) — Unix timestamp for 00:00 UTC on Sunday.

Reading 2025's weeks as epoch ranges

A Unix timestamp pins an instant; an ISO week names a seven-day span. Reporting tools constantly translate between the two — a log line becomes "week 9", or a weekly report becomes an epoch range to query. In 2025, that mapping is concrete: week 1 opens at epoch 1735516800, and week 52 closes at 1767484799, the final second of Sunday, Dec 28, 2025.

• Epoch 1735516800 → 00:00 UTC on Monday of week 1 (Dec 30, 2024).
• Epoch 1767484799 → 23:59:59 UTC on Sunday of week 52 — one second before 1767484800 would tick over to the next ISO year's week 1.
• Any week's span → its start epoch up to start + 604,799 seconds; exactly 604,800 seconds per week, no exceptions (UTC has no DST).

Why 2025 has 52 weeks

The count falls out of one rule: ISO week 1 is the week containing the first Thursday, and weeks run Monday–Sunday. 2025 starts on a Wednesday, which keeps it a 52-week year; the days after week 52 belong to week 1 of 2026. December 31, $2025 closes on a $Wednesday, and the last week ends $on Dec 28, 2025, still inside 2025

How 2025's weeks line up against neighboring years

The same calendar date rarely keeps its week number from one year to the next, because each January 1 lands on a different weekday. March 1, 2025 sits in ISO week 9; in 2024 and 2026 it will sit one week off in either direction. The tables for the adjacent years make the drift visible:

• Week numbers for 2024 (52 weeks)
• Week numbers for 2025 (52 weeks)
• Week numbers for 2026 (53 weeks)
• Week numbers for 2024
• Week numbers for 2026

Examples: 2025's weeks at the epoch boundaries

• January 1, 2025 (Wednesday) falls in ISO week 1 of ISO year 2025.
• December 31, 2025 (Wednesday) falls in ISO week 1 of ISO year 2026.
• March 1, 2025 sits in ISO week 9 — the sort of date whose week number shifts year to year.

Week Numbers for 2025 — ISO Week List — questions from actual use

What are the week numbers for 2025?

2025 has 52 ISO weeks. Week 1 runs Dec 30, 2024 to Jan 05, 2025 — it starts in December 2024, because ISO week 1 is the week containing the first Thursday, and 2025's first Thursday pulls the week start back into 2024, and week 52 runs Dec 22, 2025 to Dec 28, 2025.

Is 2025 a 52-week or 53-week year?

2025 is a 52-week year (January 1 was a Wednesday). The next 53-week year is 2026, because its January 1 falls on the right weekday to spill into a 53rd week.

When do 2025's week numbers and dates disagree?

Day-of-year and week-of-year counting disagree at the edges. January 1, 2025 (Wednesday) sits in ISO week 1 of 2025, and December 31 (Wednesday) lands in week 1 of 2026 — already week 1 of 2026. The ISO year owns the days its weeks' Thursdays fall in, so a few days each December and January always belong to the neighboring year.

What epoch timestamps belong to a week in 2025?

Each week on this page shows two Unix timestamps: 00:00 UTC on its Monday (the start) and 00:00 UTC on its Sunday. For 2025, those run from 1735516800 for the start of week 1 to 1767484799 for the last second of week 52 — a span of exactly 31,449,600 seconds across 52 weeks.