Day of the Week Calculator
Find the day of the week for any date, with its ISO week number, day of the year and whether it's a leap year.
Day of the week
Sunday
- Week number (ISO)
- 43
- Day of the year
- 298 of 365
- Days left in the year
- 67
- Is 2026 a leap year?
- No
25 October 2026 is a Sunday, day 298 of 2026, in ISO week 43.
How it's worked out
- Date25 October 2026
- ISO week
weeks start on Monday; week 1 holds the year's first Thursdayweek 43
How it's worked out
The date is counted as a number of days from a fixed starting day, and the remainder after dividing by 7 gives the weekday.
Worked example
25 October 2026 is a Sunday. It's day 298 of 2026, in ISO week 43, and 2026 is not a leap year.
Questions people ask
What day of the week was I born?
Enter your date of birth and the calculator shows the weekday, for any year.
How are week numbers counted?
By the ISO 8601 standard: weeks start on Monday, and week 1 is the week containing the year's first Thursday. Some years have 53 weeks.
Which years are leap years?
Years divisible by 4, except century years not divisible by 400. 2024 and 2000 were leap years; 1900 was not.
About this calculator
Formula and rules last checked 25 October 2026Written and tested by the CalcPenguin teamReport a problem
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