Calculate the exact difference between two dates in days, weeks, months and years — this date and time duration calculator is handy for deadlines, ages, countdowns, and event planning.
The difference is measured in calendar days between the two dates, then converted to weeks and years for context (using 365.25 days/year to account for leap years).
Date calculators typically perform two kinds of operations: finding the difference between two dates (in days, weeks, months, or years), or adding/subtracting a duration from a starting date. Both require correctly handling variable month lengths and leap years, which don't follow a simple fixed-day pattern.
Converting a day count into years, months, and days requires walking through the calendar and adjusting for each month's actual length, rather than using a flat average, to get a precise breakdown rather than just a rough approximation.
This is why 2000 was a leap year, but 1900 was not — 1900 is divisible by 100 but not by 400, while 2000 is divisible by both.
| Month | Days |
|---|---|
| Jan, Mar, May, Jul, Aug, Oct, Dec | 31 |
| Apr, Jun, Sep, Nov | 30 |
| Feb | 28 (29 in leap years) |
Example 1 — Days between two dates: From 1 January 2026 to 13 August 2026 is 224 days — 31 (Jan remaining) + 28 (Feb) + 31 (Mar) + 30 (Apr) + 31 (May) + 30 (Jun) + 31 (Jul) + 12 (Aug) = 224.
Example 2 — Adding days to a date: A 90-day payment term starting 13 August 2026 lands on 11 November 2026 — counting forward day by day across August (18 remaining), September (30), October (31), and 11 more days into November.
Example 3 — Business days only: Between 3 August 2026 (Monday) and 14 August 2026 (Friday), there are 11 calendar days but only 9 business days once the two weekend days are excluded.
| Use case | What's typically calculated |
|---|---|
| Contract/lease terms | Duration in months/years between start and end dates |
| Project deadlines | Adding a number of business days to today |
| Countdown to an event | Days remaining until a future date |
| Legal notice periods | Exact calendar days from a trigger date |
How do I use a date calculator to find someone's date of birth from their age? Enter today's date and subtract the person's age in years to estimate their birth year, then narrow the exact date if you know their birthday — this calculator handles the day-count math for you either direction.
What is 9 months from today? Add 9 months to today's date using the calculator above — this is commonly used to estimate a pregnancy due date, though a dedicated due date calculator accounts for weeks instead of calendar months.
Why do I get a different day count than a simple year × 365 estimate? Leap years add an extra day roughly every four years, so precise counts over multi-year spans differ from a flat 365-day-per-year approximation.
How are business days different from calendar days? Business days exclude weekends (and often public holidays), so the count is always equal to or lower than the calendar-day difference.
What happens when adding a month lands on a day that doesn't exist? Most conventions roll the date back to the last valid day of the target month (e.g., Jan 31 + 1 month = Feb 28 or 29).
Is the day count inclusive or exclusive of the start and end date? Conventions vary — some contexts (like counting nights of a hotel stay) exclude one endpoint, while others (like counting total days including both) include both; always check which convention applies to your specific use case.
How do I calculate a date a certain number of weeks from today? Multiply the number of weeks by 7 to get total days, then add that day count to today's date, adjusting for month-length and leap-year rules along the way.
Do date calculators account for time zones? Most basic date-difference calculators work on calendar dates only, without time-of-day or time-zone precision — for exact elapsed-time calculations across zones, a dedicated datetime tool is more appropriate.
Why might two people calculate a different number of months between the same two dates? "Months between" can be measured as whole completed months (like age) or as a fractional/rounded value — different rounding conventions produce different results from the same date range.
How many days until Christmas? It depends on today's date — enter today's date and December 25 into the calculator above to get the exact day count instantly, updated automatically every day.
| Question | Answer |
|---|---|
| How many weeks in a year? | ≈ 52.14 weeks |
| How many hours in a year? | 8,760 hours (8,784 in a leap year) |
| How many hours in a week? | 168 hours |
| How many seconds in a day? | 86,400 seconds |
| How many seconds in a year? | 31,536,000 seconds (365-day year) |
| How many days in a year? | 365 days (366 in a leap year) |
From January 1, 2026 to December 31, 2026 is 364 days (not 365, since it counts the difference between the two dates rather than a full calendar year span) — enabling an 'include end day' option would add one more day to reach 365.
Leap year: A year with an extra day (February 29) added to keep the calendar aligned with Earth's orbit.
Elapsed time: The total duration between two points in time.