How does adding or subtracting a date work?
The calculator applies calendar years and months first, then weeks and days. This is different from treating every month as a fixed number of days.
What happens at the end of a month?
If a requested target month does not contain the original day number, the date is clamped to the last valid day of that month.
Why are weeks converted to seven days?
A calendar week is treated as seven consecutive calendar days for this arithmetic. It does not automatically skip weekends.
Can I use this for business-day scheduling?
For workday counting that skips weekends and optionally Federal holidays, use the Business Days Calculator instead.
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Frequently asked questions
Yes. You can enter any combination of nonnegative amounts.
Yes. Select Subtract before calculating.
The result is clamped to the last valid day of February.
No. In a non-leap target year it clamps to February 28.
No. This is calendar-date arithmetic; weekends count like other calendar days.
No. Use the Business Days Calculator when holiday exclusions are needed.
Yes. Calendar arithmetic automatically carries across months and years.
The calculation runs locally in the browser and does not require sign-up.
Sources and methodology
This calculator uses transparent browser-side date/time arithmetic. The references below provide standards or official context relevant to the calculation.
ISO — ISO 8601 date and time formatInternational standard context for unambiguous Gregorian dates, times, UTC and intervals.ISO — ISO 8601-1:2019Current published ISO standard for Gregorian date and time representations.
Date and time scope: Calendar, time-zone, holiday and scheduling conventions can differ by jurisdiction or organization. Check authoritative rules when a deadline, legal right, payroll event or travel schedule depends on the exact result.
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