Week Numbers for 2020 — ISO Week List

Week numbers for 2020

2020 has 53 ISO weeks. Week 1 starts on Dec 30, 2019 and week 53 ends on Jan 03, 2021. 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 2020, that end value is 1578182400; 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 2020'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 2020, that mapping is concrete: week 1 opens at epoch 1577664000, and week 53 closes at 1610236799, the final second of Sunday, Jan 03, 2021.

• Epoch 1577664000 → 00:00 UTC on Monday of week 1 (Dec 30, 2019).
• Epoch 1610236799 → 23:59:59 UTC on Sunday of week 53 — one second before 1610236800 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 2020 has 53 weeks

The count falls out of one rule: ISO week 1 is the week containing the first Thursday, and weeks run Monday–Sunday. 2020 qualifies for 53 weeks because January 1 was a Wednesday in a leap year, which stretches week 1 far enough that a 53rd week fits before next year's week 1 begins. December 31, $2020 closes on a $Thursday, and the last week ends $in January 2021

How 2020'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, 2020 sits in ISO week 9; in 2019 and 2021 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 2021

Examples: 2020's weeks at the epoch boundaries

• January 1, 2020 (Wednesday) falls in ISO week 1 of ISO year 2020.
• December 31, 2020 (Thursday) falls in ISO week 53 of ISO year 2020.
• March 1, 2020 sits in ISO week 9 — the sort of date whose week number shifts year to year.

Week Numbers for 2020 — ISO Week List — questions from actual use

What are the week numbers for 2020?

2020 has 53 ISO weeks. Week 1 runs Dec 30, 2019 to Jan 05, 2020 — it starts in December 2019, because ISO week 1 is the week containing the first Thursday, and 2020's first Thursday pulls the week start back into 2019, and week 53 runs Dec 28, 2020 to Jan 03, 2021. The final week spills into January 2021.

Is 2020 a 52-week or 53-week year?

2020 is a 53-week year: it started on a Wednesday in a leap year, so February 29 pushes the calendar far enough for a 53rd week. The next 53-week year after 2020 is 2026.

When do 2020's week numbers and dates disagree?

Day-of-year and week-of-year counting disagree at the edges. January 1, 2020 (Wednesday) sits in ISO week 1 of 2020, and December 31 (Thursday) lands in week 53 of 2020. 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 2020?

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 2020, those run from 1577664000 for the start of week 1 to 1610236799 for the last second of week 53 — a span of exactly 32,054,400 seconds across 53 weeks.