Time & Date · Date Math
Deadline & Notice Period Calculator
Work out the last day of a notice period, a payment or filing deadline, or any period of N days, weeks or months that starts on a given date — counting the start day or not, and in calendar or working days.
A ready-made version of the Date Add/Subtract Calculator.
How this is calculated
Result = Start ± N units; months/years keep the day of the month, or use the last day if that month is shorter
- Working days
- Days that aren't weekend days or listed holidays; the start date itself isn't counted
- Day 1 option
- Counts the start date as the first day of the period (result one day earlier)
Adding days and weeks is plain counting. Months and years follow the calendar: 15 March + 1 month is 15 April, and when the target month is shorter the date moves to that month's last day — 31 January + 1 month is 28 or 29 February, not early March. Working days skip your weekend days and any holidays you list, which is how most deadlines and delivery estimates are counted.
Assumptions & sources
- Dates are calendar dates (no time of day or time zones).
- The start date isn't counted unless you turn on 'Count the start date as day 1'.
- Holidays only matter when they fall on working days.
- 1ISO 8601 — Date and time format (week numbering, calendar dates) — International Organization for Standardization
- 2Calendrical Calculations (Reingold & Dershowitz) — Cambridge University Press
Calculator ID TIME-DATEADD-001/deadline · version 2.0.0
Common questions
If I resign on 1 October with 90 days' notice, when is my last day?
If the resignation day counts as day 1 — the usual reading of employment notice periods — the 90th day is 29 December. If counting starts the next day, it's 30 December. Check your appointment letter for the exact wording.
Are notice periods in calendar or working days?
Usually calendar days or months. Some contracts and statutory deadlines use working days — switch the unit to 'Working days' for those.
What about deadlines that fall on a holiday?
Many rules move the deadline to the next working day. This calculator shows the plain date and warns if it falls on a weekend; add holidays and use working days if your rule needs it.