Date difference
Count days, weeks, and calendar years/months between two dates.
Your inputs
Choose your dates and the calculation convention. Results update as you edit.
Calculations run in your browser. Inputs are not saved or sent to analytics.
Your result
Complete the inputs to see your result.
How it works
- Total days = End date − Start date
- Include end date (+1): +1
- Whole weeks = floor(Total days ÷ 7)
Assumptions and limitations
Civil dates use the proleptic Gregorian calendar, years 1–9999. Whole years use anniversaries, then up to 11 completed months and remaining days; month ends are clamped. A February 29 birthday in a non-leap year uses your selected February 28 or March 1 convention. Dates stay in your browser.
Sources
- US Naval Observatory — Calendars and conversion algorithms Sources reviewed: 2026-10-05
