Age & Date Calculator
Enter a start date (such as a birth date) and an end date to get the gap as whole years, months and days, plus the total number of days between them. Both dates stay in your browser.
Runs in your browser
Free, no sign-up. Both dates are calculated in your browser and never uploaded, saved or put in analytics. Usage events record only that a calculation happened, not the dates.
Age & Date Difference Calculator
Calculate the exact difference between two dates.
Select a start date and end date to see the difference.
How to use the Age & Date Calculator
- Pick or type a Start Date, for example a birth date. The end date must be the same day or later.
- Pick or type an End Date, for example today.
- Read the Result panel: the gap in years, months and days, and below it the total difference in days.
- Press Reset to clear both dates. If the end date is before the start date, or a date is invalid, the panel shows an error instead of a result.
Worked example
Sample data
Start Date: 1990-03-15 End Date: 2025-09-10
35 years, 5 months, 26 days Total difference: 12,963 days
Whole years are counted first (to 2025-03-15), then whole months (to 2025-08-15), and the remaining 26 days are left over.
How it works
How years, months and days are counted
The tool first counts whole calendar years from the start date, then whole calendar months, and the days left over. It is a calendar difference, not an average-length one.
When the start day does not exist in a month, the date is moved back to that month's last day. For example 31 January plus one month is treated as 29 February in a leap year, so 2024-01-31 to 2024-03-01 reads as 1 month, 1 day.
The total-days figure is the plain number of days between the two dates. The end date itself is not counted as an extra day.
total days = (end date - start date) / 86,400,000 ms, on UTC midnight dates
Age on a leap day
A person born on 29 February reaches an anniversary on 28 February in non-leap years under this method, so 2024-02-29 to 2025-02-28 gives exactly 1 year. Legal rules for when a leap-day birthday counts differ between countries; this tool does not apply any of them.
Inputs, outputs and limits
Inputs
- Start Date
- End Date
Outputs
- Years, months and days between the dates
- Total difference in days
Limits
- Gregorian calendar dates only, entered through your browser's date field.
- The end date must be the same as or after the start date; there is no negative result.
- Dates have no time of day or time zone; each is treated as a calendar date.
- No business-day, holiday or time-of-day calculation.
Processing
- Both dates are calculated in your browser and never uploaded, saved or put in analytics. Usage events record only that a calculation happened, not the dates.
Frequently asked questions
Do my dates leave my device?
No. The calculation runs in this page's JavaScript. The dates are not sent to a server, stored, or included in analytics events, and a shared link never contains them.
Can I use it as an age calculator?
Yes. Enter the birth date as the start and today's date (or any date you want to measure to) as the end. The years, months and days are the person's age on that date.
Why is the end date before the start date an error?
The tool only measures forward gaps. Swap the two dates if you want the difference the other way round.
Is the end date counted as a day?
No. From 2025-01-01 to 2025-01-02 is 1 day. If you need an inclusive count (both days counted), add 1 to the total.
Why do months of different lengths give odd day counts?
Months are counted as calendar months, so the leftover days depend on which month you land in. 15 January to 15 February is 1 month, 0 days even though it is 31 days.
Need this workflow inside your product?
We build calculators, converters and processing steps like this one directly into your web or mobile product, with your rules and branding.