Analyze Calendar Date

Enter any calendar date and it reports the day of the week, the day-of-year number (1 to 366), the ISO week number, the quarter, how many days remain in the year, and whether the year is a leap year. One lookup replaces a handful of separate calculations.

ISO 8601 defines week 1 as the week containing the year’s first Thursday, with weeks starting on Monday. This means January 1 can fall in week 52 or 53 of the previous year, and December 31 can fall in week 1 of the next. Payroll, manufacturing, and European business calendars all use this standard, which is why the number sometimes surprises people.

The full Gregorian rule: divisible by 4, except century years, unless divisible by 400. So 2024 is a leap year, 1900 was not, 2000 was. The tool applies this exactly, which matters for day-of-year counts after February.

The number of seconds between January 1, 1970 (UTC) and midnight of your chosen date. It is how most databases, APIs, and programming languages represent moments internally. Handy when you need a quick value for testing or comparing against an API response.

Developers verifying date arithmetic and timezone handling, project managers translating dates to ISO weeks for planning tools, students checking homework on day-of-year problems, and anyone settling questions like which weekday a birthday falls on or how many days remain until year end.

No. All calculations run in your browser using JavaScript’s built-in date functions. Nothing is uploaded, logged, or stored, and the tool works offline once loaded.