Date to Day Converter
Enter any date to find its day of the week, ISO week number, day of year, quarter, and whether it falls in a leap year.
✓ Runs in your browser · Updated 2026-03-31Enter values and click Find the Day to see results
How the Day of the Week Is Determined
JavaScript's Date.getDay() returns 0 for Sunday through 6 for Saturday. The ISO standard numbers days from 1 (Monday) to 7 (Sunday). This tool shows both the name and the ISO day number.
ISO Week Numbering
ISO 8601 defines week 1 as the week containing the first Thursday of the year. Weeks start on Monday. A year has either 52 or 53 ISO weeks. The calculation uses the "nearest Thursday" method.
Day of Year: (Date − Jan 1) / 86,400,000 + 1
Leap Year: Divisible by 4 AND (not by 100 OR by 400)
Leap Year Rules
A year is a leap year if it is divisible by 4, except for century years which must also be divisible by 400. So 2000 was a leap year, but 1900 was not. Leap years have 366 days with February having 29 days.
Related Tools
Get the ISO week details with the Week Number Calculator. See your date in multiple display formats using the Date Formatter.
Frequently Asked Questions
How do I find what day of the week a specific date falls on?
Enter any date into this tool and it will instantly tell you the day of the week (Monday, Tuesday, etc.) for that date.
Can I check the day for past or future dates?
Yes, this tool works for any valid date — past, present, or future. You can check which day you were born on or what day a future event falls on.
On which day does 15th August 2026 fall?
You can enter 15/08/2026 in the tool to find out. Independence Day 2026 falls on a Saturday.