Date Duration Calculator
Find the exact time between any two dates — total days, weeks, and a calendar breakdown in years, months, and days.
Enter a start and end date to see how much time sits between them: total days, full weeks, and a calendar-accurate breakdown (years, months, days) that respects real month lengths and leap years. Handy for project timelines, pregnancy math, anniversaries, and countdowns.
How to use this calculator
- Step 1: Pick your start date using the date picker.
- Step 2: Pick your end date — order doesn't matter.
- Step 3: Click Calculate.
- Step 4: Read the total days, the weeks breakdown, and the calendar (years/months/days) breakdown.
The formula
totalDays = round((end − start) / 86,400,000); calendar breakdown borrows across months using actual month lengths
Worked example
From March 10, 2024 to June 25, 2024 there are 107 days — 15 weeks and 2 days, or 3 months and 15 days in calendar terms.
Frequently Asked Questions
How does the date duration calculator count months?
It counts full calendar months, not 30-day blocks. From March 10 to June 10 is exactly 3 months; leftover days are counted separately. When the end day is earlier in the month than the start day, it borrows days from the actual preceding month, so February correctly contributes 28 or 29 days depending on the year.
Does it handle leap years?
Yes. Month lengths come from the real calendar, so February 29 exists in leap years and the day counts are exact. For example, February 28 to March 1 is 2 days in 2024 (a leap year) but only 1 day in 2023. The total-days figure is computed from the true millisecond difference, so it can never drift.
What happens if I enter the end date before the start date?
The calculator simply swaps them — duration is order-independent, so you get the same answer either way. This keeps it forgiving when you're quickly checking how long ago something happened versus how far away it is.
What's the difference between total days and the year/month/day breakdown?
Total days is the raw count of 24-hour days between the dates. The breakdown expresses the same span in calendar units: full years first, then full months, then remaining days. Both describe the same duration — use total days for precise counts (billing, deadlines) and the breakdown for human-friendly reading (ages, anniversaries).
Does it count the start day, the end day, or both?
It counts the elapsed time between the two midnights, which is the standard convention: January 1 to January 2 is 1 day. If you need an inclusive count (counting both endpoints, common for hotel nights or rental days), add 1 to the total.