Date Calculator
Add or subtract days, weeks, months, or years from a date — or find the difference between two dates.
Result date
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What is Date Calculator?
A date calculator lets you either add or subtract a span of time from a given date, or compute the exact difference between two dates. It's useful for project deadlines, scheduling, legal timeframes, and any situation where you need to know what date falls a certain number of days, weeks, months, or years away.
How to use
- 1 Choose a mode: 'Add / Subtract' to offset a date, or 'Difference' to measure the gap between two dates.
- 2 In Add/Subtract mode: pick a start date, enter the number of units, select the unit type, and choose whether to add or subtract.
- 3 In Difference mode: enter both a start date and an end date.
- 4 Results appear instantly below the inputs.
Formula
Example calculation
Adding 90 days to June 1, 2025 gives August 30, 2025. The difference between January 1, 2024 and June 22, 2026 is 903 days, 128 weeks, 29 months, and 2 years.
Frequently asked questions
Does the calculator account for leap years?
Yes. All arithmetic uses the JavaScript Date object, which correctly handles leap years and varying month lengths.
What does 'add 1 month' mean for January 31?
Adding one month to January 31 yields February 28 (or 29 in a leap year) since February doesn't have 31 days. The date clamps to the last valid day of the resulting month.
Can I calculate negative differences?
In Difference mode, the calculator always returns the absolute difference regardless of which date is earlier.