Day of the Week Calculator guide
Day of the Week Calculator: What Day Was It?
Use our day of the week calculator to find what day any date falls on, past or future, with the day of the year and week number.
By the AllCalculator editorial teamUpdated 16 October 20261 min read
What day were you born on? What day is Christmas this year? Our Day of the Week Calculator tells you for any date.
How to use the calculator (Day of the Week Calculator)
Choose a date, or leave it blank for today. You'll see:
- The day of the week
- The day of the year, such as day 289 of 365
- The ISO week number used in many diaries and work planners
- Whether it's a leap year
- What day the same date falls on in nearby years
A worked example
Christmas Day 2026, 25 December, is a Friday. It's day 359 of the year, in week 52.
Why the day moves each year
A normal year is 365 days, which is 52 weeks and 1 day. So a date usually moves forward one day of the week each year, and two days after 29 February in a leap year.
ISO week numbers
Week 1 is the week (Monday to Sunday) that contains the year's first Thursday. That means 1 January can fall in week 52 or 53 of the year before.
Frequently asked questions
Does it work for very old dates?
It uses the Gregorian calendar, which Britain adopted in 1752. Dates before then were recorded in the older Julian calendar, so historical records may differ.
What's a leap year?
A year divisible by 4, except century years, which must be divisible by 400. So 2000 was a leap year, but 1900 wasn't.
To add days or months to a date, use our Date Calculator.
Sources and further reading
Links open official and independent websites in a new tab.
This guide is general information to help you understand your options. It isn't financial, tax, legal or building advice and doesn't take your personal circumstances into account. Figures were checked when the guide was last updated and can change, so confirm anything important with GOV.UK, HMRC, a regulated adviser or a qualified tradesperson.