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.

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The "End epoch (UTC)" column shows the Unix timestamp for 00:00 UTC on the Sunday of that week, which is the first second of the last day of the week. The last second of the week is one second before the Monday start of the next week.

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.

Why week numbers pair with epoch time

A Unix timestamp is a single number for an instant. The ISO week number is a label for a seven-day span. Converting between them is common in reporting: a log timestamp becomes "week 36", and a week label becomes the epoch range for that week. Use the timestamps in this table with the epoch converter to move between a week and its Unix time in either direction.

• Epoch $1735516800 → Monday start of ISO week 1 of $2025.
• Epoch $1736035200 → Sunday end of ISO week 1 of $2025.
• Epoch $1766361600 → Monday start of ISO week $52 of $2025.
• Epoch $1766880000 → Sunday end of ISO week $52 of $2025.

52-week and 53-week years

Under ISO 8601, a year has 53 weeks when the year starts on a Thursday, or when it is a leap year that starts on a Wednesday. Otherwise it has 52 weeks. That is why the number of weeks in a year is not always 52 — it is 52 most years, and 53 about once every five or six years.

• $2025 is a $52-week year under ISO 8601.
• Week 1 of $2025 starts on $Dec 30, 2024.
• Week $52 of $2025 ends on $Dec 28, 2025.

Comparing week numbers across years

Week numbers shift from year to year because each year starts on a different day of the week. A date like March 1 can be in week 9 in one year and week 10 in another. Comparing the week-number tables for consecutive years is the fastest way to see that shift:

• 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

• January 1, $2025 falls in ISO week $1 of $2024.
• Today ($Sep $18, $2025) falls in ISO week $— of $2025 — $n/a.
• ISO week 1 of $2025 runs from $Dec 30, 2024 to $Jan 05, 2025.
• ISO week $52 of $2025 runs from $Dec 22, 2025 to $Dec 28, 2025.