Add, subtract, and measure dates.
Add or subtract years, months, weeks, and days from any date, or measure the exact gap between two dates in years, months, days, weeks, and business days. Calendar math done for you, leap years and month lengths included.
What do you need?
What this tells you
The numbers at a glance
Common intervals from this date
Handy reference for deadlines and payment terms such as Net 30 and Net 60.
| Interval | Earlier date | Later date | Later weekday |
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Date math, explained
How Date Arithmetic Works
Date arithmetic adds or subtracts calendar units from a starting date. Years are added first, then months, then days. When adding months, if the resulting day exceeds the month length (for example, adding one month to January 31 gives February 28 or 29), the date is adjusted to the last valid day of that month.
Common Uses for Date Calculations
Date calculations are essential for determining deadlines, contract expiration dates, warranty periods, and project timelines. Lawyers use them for statute of limitations, businesses for payment terms (Net 30, Net 60), and individuals for countdown planning.
Handling Leap Years and Month Lengths
This calculator automatically handles leap years and varying month lengths. February has 28 days in common years and 29 in leap years. Months range from 28 to 31 days, and the calculator adjusts accordingly when crossing month boundaries.
Business Days vs Calendar Days
This calculator counts calendar days, which include weekends and holidays. If you need business days only, subtract approximately 2 days for every 7 calendar days. For precise business-day calculations, a dedicated business day calculator is recommended.
Common questions
What happens when I add one month to January 31?
Adding one month to January 31 results in February 28 (or February 29 in a leap year). The calculator adjusts to the last valid day of the target month when the original day number exceeds the month length.
Can I add days, months, and years at the same time?
Yes. The calculator applies years first, then months, then days, in that order. You can combine all three for complex date arithmetic in a single calculation.
Does this account for daylight saving time?
The calculator works at the date level and is not affected by daylight saving time changes. It counts full calendar days regardless of clock adjustments.
How do I calculate a date in the past?
Select the Subtract operation and enter the number of days, months, or years you want to go back. The calculator will return the earlier date.
Calendar days only. Business-day counts exclude weekends but not public holidays, which vary by country, state, and employer. Verify legal or contract deadlines against the exact terms that apply to you.