Add or Subtract Days Calculator
Add or subtract any whole number of days from a calendar date.
This tool runs entirely in your browser. Your files are never uploaded to a server.
What this tool does
Adds or subtracts a whole number of days from a calendar date and shows the resulting date, calculated using UTC-based arithmetic so the day count isn't shifted by your local time zone.
How to use it
Pick a starting date, choose Add or Subtract, and enter how many days. Reset returns to the default example: adding 7 days to 2026-01-01.
Worked example
Adding 7 days to 2026-01-01 (a Thursday) lands on 2026-01-08, also a Thursday, since 7 is a multiple of 7. Subtracting 7 days from the same starting date instead lands on 2025-12-25.
Method
The starting date is parsed as year-month-day and built as a UTC date using Date.UTC, so the calculation isn't affected by daylight-saving changes or your browser's local offset. The chosen number of days is then added to or subtracted from that UTC date, and the result is formatted in UTC using your browser's locale for weekday and month names.
Whole-day amounts only
The amount must be a whole number — fractional days like 2.5 aren't accepted and produce no result, since adding a fraction of a day to a calendar date isn't well-defined without also specifying a time of day.
Limitations
This calculator works in fixed calendar days; it doesn't skip weekends or holidays, so if you need a business-day count instead, use the Working Days Calculator. It also only accepts a date typed or picked in YYYY-MM-DD form, not a date and time together — for that, use the Add or Subtract Time Calculator.
Privacy and processing
The calculation runs entirely in your browser using JavaScript's Date object. The date you enter is never uploaded or stored.
Frequently Asked Questions
- Why does this use UTC instead of my local time zone?
- Calculating in UTC avoids the date shifting by a day near midnight due to your local time zone offset or daylight-saving changes — the result reflects pure calendar-day arithmetic.
- Can I add or subtract a fractional number of days?
- No, the amount must be a whole number. A calendar date has no fractional day component, so entering something like 2.5 produces no result.
- Does this skip weekends or holidays?
- No, it adds or subtracts fixed calendar days regardless of weekday. For a business-day count that excludes weekends, use the Working Days Calculator instead.