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Week Number Calculator

Worked example result
ISO week number1
ISO week year2026
Day of year1

January 1, 2026 is a Thursday, so it falls in ISO week 1 of 2026 — the first day of the year is also day 1 of week 1.

Shift the date to the Thursday of its week; Week = 1 + whole weeks between that Thursday and the first Thursday of the ISO year · Powered by CalcHub — Week Number Calculator