Week Number Calculator

Find the ISO 8601 week number for any date, the week’s Monday–Sunday range, day of the year and quarter.

What is the Week Number Calculator?

ISO week numbers are used in business planning and software. Week 1 is the week containing the first Thursday of the year.

How does it work?

The date is shifted to the Thursday of its week, and the week number is counted from the start of that Thursday’s year.

Formula

Week = ⌈(day-of-year of that week’s Thursday) ÷ 7⌉

Example

1 January 2021 was in ISO week 53 of 2020, because that week’s Thursday fell in 2020.

Frequently asked questions

What is the Indian financial-year quarter?

The financial year runs April–March, so Q1 is April–June and Q4 is January–March.

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