Days are consecutive calendar days
One day moves to the next calendar date. The calculation uses date-only values rather than time or timezone offsets.
046 · DATE & TIME
Date Add & Subtract Calculator
Add or subtract days, weeks, months, or years from a date and instantly see the resulting date and weekday.
LOCALDate calculations run only in your browser.
LOCALDates and results are processed only in your browser and are not sent to or stored on a server.
Quick calculationsCommon date shifts
Result Date
Enter a start date and quantity.
HOW TO USE
How to use
- 01
Choose a start date.
- 02
Choose Add or Subtract and select days, weeks, months, or years.
- 03
Enter a non-negative whole-number quantity and calculate.
- 04
Review the resulting date and weekday, then copy it if needed.
DATE ARITHMETIC GUIDE
Rules for adding and subtracting dates
Keep days and weeks separate from calendar months and years, with explicit month-end, leap-year, zero-value, and supported-range behavior.One week is exactly seven days
Weeks are calculated as seven consecutive calendar days, not by calendar week number.
Months use calendar-month arithmetic
The tool never converts 30 days into one month. If the target month lacks the same day, it clamps to the last day of that month.
Years use calendar-year arithmetic
The tool never converts 365 days into one year. February 29 clamps to February 28 when the target year is not a leap year.
Inputs stay in the browser
Selected dates and results are processed locally without server storage or transmission.
IMPORTANT NOTES
Important notes
- Quantity must be a non-negative integer.
- One month is not the same as 30 days, and one year is not the same as 365 days.
- If the result would exceed the supported date range, the tool shows an error instead of a result.
- Business-day and holiday exclusion belongs to TOOL050 and is not applied here.
FAQ
Frequently asked questions
01What is January 31 plus one month?+
If the target month has no 31st, the result is clamped to that month’s last day. In 2026 that is February 28.
02What is February 29 plus one year?+
If the target year is not a leap year, the result is February 28.
03Are 30 days and one month the same?+
No. Thirty days means consecutive calendar days, while one month moves by the calendar month.
04What happens when I add or subtract zero days?+
The result stays on the same date.
05Are my dates uploaded?+
No. The calculation runs locally in the current browser.