A four-week lead time
2026-11-07 plus 4 weeks is 2026-12-05. Both dates are Saturdays, separated by 28 calendar days.
Add or Subtract Weeks from a Date
Move a date forward or backward by whole weeks. Find a deadline, reverse-plan a start date, and see the resulting ISO week number.
Result date
Monday, December 7, 2026
2026-11-09 plus 4 weeks (28 calendar days).
- Result date
- 2026-12-07
- ISO week
- 2026-W50
- Signed change in days
- 28
Shared links pin the reference date so the result is reproducible. Dates are in the URL; avoid sharing private milestones. Parameterized results are marked noindex.
How this calculator works
One week is exactly seven calendar days. Multiply the signed number of weeks by seven and add it to the start date. The weekday stays the same, including across leap days and New Year. A negative number moves backward; zero leaves the date unchanged.
Calculations use calendar dates, not local clock timestamps. Changing clocks for daylight saving does not turn a seven-day date interval into a shorter or longer week. Supported years are 1000–9998, and results must stay within that range.
Worked examples
Work backward from a launch
2027-01-15 minus 6 weeks is 2026-12-04. Enter -6 to find the planning start date.
Cross a leap day
2024-02-28 plus 1 week is 2024-03-06. February 29 is counted automatically.
Use the date, then check the week
The resulting ISO week is a calendar label, not the number of weeks added. For example, adding one week to December 28, 2026 gives January 4, 2027, in ISO 2027-W01. This calculator does not move deadlines off weekends or public holidays.
FAQ
Is adding four weeks the same as adding one month?
No. Four weeks always means 28 days. Calendar months have 28, 29, 30, or 31 days, so a month-based deadline can land on a different date.
Are weekends and holidays included?
Yes. These are calendar-day calculations. They do not count business days, skip holidays, or adjust a result to a working day.