Date Calculator
Add or subtract days, months, and years from any date. Find what date it will be after a given number of days.
Result Date
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Year —
Month —
Day —
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Result Date
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Year —
Month —
Day —
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After Adding
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After Subtracting —
Result Year (+) —
Result Month (+) —
Result Day (+) —
Days Between Results —
How to Use This Calculator
- Enter the start date (year, month, day).
- Choose Add or Subtract.
- Enter the number of days, months, and/or years to offset.
- The result date is shown in the results panel.
Formula
Result = Start Date ± (Years + Months + Days)
Years are added first, then months, then days, so month-end edge cases are handled correctly.
Example
Example: Start date Jan 31, 2024 + 1 month = Feb 29, 2024 (leap year). Add another month = Mar 29, 2024.
Frequently Asked Questions
- Enter the start date (year, month, day), set the operation to "Add", and enter the number of days, months, or years you want to add. The result date is shown instantly. For example, adding 45 days to March 15, 2025 gives April 29, 2025. The calculator handles month-end rollovers automatically: adding 1 month to January 31 produces February 28 (or 29 in a leap year), because February does not have a 31st. This is important for subscription billing and contract end dates where "one month" from the 31st might mean different things.
- Yes — set the Operation field to "Subtract" and the calculator moves the start date backward by the number of days, months, or years you specify. For example, subtracting 90 days from today gives the date 90 days ago, useful for finding the start of a 90-day period, statute of limitations dates, or warranty start dates. Subtracting months also handles month-end edge cases: subtracting 1 month from March 31 gives February 28 (or 29 in a leap year), not March 3 or another overshoot date.
- Enter today as the start date and add 90 days in the days field. The result shows the exact future date. For example, if today is January 15, 2026, then 90 days later is April 15, 2026 (since January has 16 remaining days: 31−15 = 16, February adds 28, and March adds 31, then April 15 fills the rest: 16+28+31+15 = 90). Ninety-day periods are commonly used in legal deadlines, probationary employment periods, investment cooling-off periods, and some medical follow-up schedules.
- Yes — the calculator uses the JavaScript Date object, which correctly applies the Gregorian calendar leap year rules. A year is a leap year if it is divisible by 4, except for century years (divisible by 100) that must also be divisible by 400. So 2000 was a leap year (400 ÷ 400 = 1), but 1900 was not (1900 ÷ 400 = 4.75). This means adding exactly 1 year to February 28, 2024 (a leap year) gives February 28, 2025 — not February 29. The calculation correctly accounts for all these calendar rules.
- Yes — fill in any combination of years, months, and days and the calculator adds or subtracts all of them from the start date. The operations are applied in order: years first, then months, then days. For example, adding 1 year, 2 months, and 15 days to March 1, 2024: first add 1 year → March 1, 2025; then add 2 months → May 1, 2025; then add 15 days → May 16, 2025. This approach matches the most intuitive interpretation of "1 year 2 months and 15 days from now" in legal and financial contexts.