Date Difference Calculator
Find the exact number of years, months, and days between two dates, or add/subtract days, weeks, months, or years from a date.
🔒 Processed locally in your browser
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How to use
- Choose "Difference between dates" to compare two dates, or "Add/subtract from a date" to do date math.
- In difference mode, pick a start and end date — the years, months, days, and total days update instantly.
- In add/subtract mode, pick a date, choose + or −, enter a number, and pick a unit (days, weeks, months, or years).
- The resulting date updates live below — there's no button to press.
Features
- Calculates the exact difference between two dates in years, months, and days, plus total days
- Adds or subtracts days, weeks, months, or years from any date
- Correctly handles month-end rollover, like Jan 31 plus one month landing on Feb 28
- Updates live as you type — no button to press
- 100% client-side — your dates never leave your browser
Frequently asked questions
How is the years/months/days difference calculated?
It's calendar-correct, not a simple division of total days by 365. The calculator finds the largest whole number of months that fit between the two dates, then counts the remaining whole days, so results match how people actually count time on a calendar.
What happens when I add a month to the 31st?
If the target month has fewer days, the result clamps to that month's last day instead of overflowing. For example, Jan 31 plus one month lands on Feb 28 (or Feb 29 in a leap year), not Mar 3.
Can I subtract time from a date instead of adding it?
Yes. Use the +/− toggle next to the amount field in "Add/subtract from a date" mode to switch between adding and subtracting.
Does the order of the start and end date matter?
No. In difference mode, you can pick the dates in either order — the calculator always shows the non-negative difference from the earlier date to the later one.
Does this tool store or upload my dates?
No. All calculations happen locally in your browser using JavaScript. Your dates are never sent to a server or saved anywhere.