How do I add days to a date?

Enter your base date, select ''Add'' as the operation, enter the number of days, and select ''Days'' as the unit. The calculator instantly shows the resulting date with full details.

Can I subtract days, weeks, or months from a date?

Yes. Select ''Subtract'' as the operation and choose your unit (days, weeks, months, or years). The calculator computes the exact resulting date accounting for month lengths and leap years.

How do I add months to a date?

Select ''Months'' as the unit and enter the number of months to add. The calculator handles variable month lengths correctly — for example, adding 1 month to January 31 gives February 28 (or 29 in a leap year).

What is the ISO date format?

ISO 8601 date format is YYYY-MM-DD (e.g. 2026-03-15). It is an international standard for representing dates unambiguously. The calculator shows your result in ISO format for easy use in code and databases.

How many days is 3 months from today?

The number of days in 3 months varies (roughly 90–92 days) because months have different lengths. Use the date add calculator: enter today''s date, select Add, enter 3, and choose Months to get the exact resulting date.

What happens when I add 1 month to January 31?

Adding 1 month to January 31 gives February 28 in a common year, or February 29 in a leap year. The calculator clamps to the last valid day of the target month rather than overflowing into March, which would be incorrect.

How do I calculate a date 90 days from today?

Enter today''s date as the base date, select ''Add'', enter 90, and choose ''Days''. The result shows the exact date 90 days from now, along with the day of the week and ISO date string.

Can I calculate what date was 6 months ago?

Yes. Select ''Subtract'' as the operation, enter 6, and choose ''Months''. The calculator will compute the date exactly 6 months before your base date, correctly handling month-end edge cases.

What is the difference between adding 1 year and adding 365 days?

Adding 1 year always lands on the same calendar date one year later (e.g., March 15, 2025 → March 15, 2026). Adding 365 days can give a different result if a leap day falls in between. Use ''Years'' for anniversary-style calculations.

Date Add / Subtract Calculator

Add or subtract days, weeks, months, or years from any date.

Base Date

Operation

Amount

Unit

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Reviewed by

Marcus Webb

Software Engineer & Developer Tools Specialist

· BSc Computer Science, University of Washington· Senior Engineer at Cloudflare (2018–2023)· Open-source contributor to Temporal API proposals

About the Date Add / Subtract Calculator

Adding or subtracting time from a date sounds simple, but months have different lengths (28–31 days) and years have different lengths (365 vs 366 days in leap years). This means "add one month" cannot always mean "add 30 days" — doing so would cause end-of-month dates to drift incorrectly.

This calculator uses proper calendar arithmetic: when you add months, it moves to the same day-of-month in the target month, clamping to the last valid day when necessary. For example, January 31 + 1 month = February 28 (not March 2). When you add years, it preserves the month and day — with February 29 clamping to February 28 in non-leap target years.

Month-End Edge Cases Explained

Operation	Result	Why
Jan 31 + 1 month	Feb 28	Feb has 28 days; result clamps to last day
Jan 31 + 1 month (leap year)	Feb 29	Feb has 29 days in a leap year
Mar 31 − 1 month	Feb 28	Feb has no 31st; clamps to 28th
Feb 29 + 1 year	Feb 28	Next year may not be a leap year
Jan 31 + 30 days	Mar 2	Day arithmetic is exact; no clamping applies

Common Use Cases

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Payment due dates — Calculate when a 30-day invoice falls due, or when a 12-month subscription automatically renews.
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Contract & notice periods — Determine the exact end date of a 90-day notice period, a 2-year lease, or a 3-month probationary period.
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Expiry & shelf life — Find when a product, prescription, or professional certification expires if issued on a known date.
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Scheduling recurring events — Plan quarterly reviews, annual renewals, or monthly check-ins by projecting dates weeks, months, or years forward.
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Construction & project planning — Add build-phase durations to a project start date to compute milestone and completion dates.

Date Add / Subtract Calculator

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About the Date Add / Subtract Calculator

Month-End Edge Cases Explained

Common Use Cases

Frequently Asked Questions