Date Duration Calculator
This date duration calculator measures the exact gap between two dates – as years, months and days, and as a total number of days and weeks – so you can answer “how long between these?” precisely.
Duration between two dates
How the date duration calculator works
It measures the gap two ways. For the total, it subtracts the start date from the end date and divides by the length of a day, giving a plain count of days that it also expresses as weeks. For the calendar breakdown, it steps through full years first, then whole months, then leftover days - so 2000-01-01 to 2026-01-01 reads as 26 years, 0 months, 0 days.
The month-and-day part borrows the correct number of days from the previous month whenever the end day is earlier than the start day, which keeps the breakdown accurate across months of different lengths. Everything runs on your device's calendar, so leap years are counted correctly and the totals never drift.
Counting age, tenure and anniversaries
A date duration calculator answers a surprising number of everyday questions: how old someone is to the day, how long you have worked somewhere, how many days a project ran, or how far apart two events fell. The years-months-days view is the natural way to state an age or a length of service, while the total-days view is better for billing, interest or streaks.
For date and time standards, the official U.S. reference is NIST at time.gov. If your span crosses public holidays that matter for work or pay, cross-check the federal holiday list at opm.gov, since this tool measures calendar duration rather than working time.
Total days versus years and months
The same duration looks very different depending on the unit. "9,497 days" and "26 years" describe the same gap, but one is better for a milestone countdown and the other for a birthday. Showing both at once means you never have to convert by hand or worry about whether a year counts as 365 or 366 days in your particular range.
A tool for milestones and deadlines
People reach for a duration calculator at the moments that matter: counting a baby's age in days, marking a work anniversary, timing a notice period, or settling a friendly argument about how long ago something happened. Because it shows the gap in several units at once, you get the framing that fits the moment without doing any conversion yourself.
It also pairs naturally with the countdown and working-day tools on this site. Use the duration calculator to look backward at how long something lasted, and the days-until calculator to look forward to what is coming next - the same underlying date math, pointed in opposite directions.
Frequently asked questions
How do I calculate the duration between two dates?
Subtract the earlier date from the later one. This date duration calculator shows the result as years, months and days, and also as a total number of days and weeks.
Does it include both the start and end dates?
The total-days figure is the gap between the two dates, not a count of calendar days touched. Two consecutive days show a duration of 1 day. Add one if you need to count both endpoints.
Can I use it to calculate age?
Yes. Enter a birth date as the start and today's date as the end, and the years-months-days breakdown is the exact age.
How does it handle leap years?
It uses your device's real calendar, so February 29 and varying month lengths are counted correctly for any range you enter.
What if I enter the dates in the wrong order?
The calculator swaps them automatically, so you always get a positive duration regardless of which date you type first.
Want a live countdown or working-day count instead? Try the days until calculator and business days calculator, or all our everyday calculators.