Date Arithmetic
Enter an ISO date-time with Z or an offset, then apply a signed number of calendar days.
Enter a valid offset-aware date-time and whole days.
A QUICK WALKTHROUGH
How to use this tool
- Enter a date-time with an explicit time-zone offset.
- Enter the whole number of calendar days to add or subtract.
- Review the resulting ISO UTC instant.
UTC calendar arithmetic
The input must include an explicit offset. Arithmetic changes the UTC calendar date by whole days and never guesses a browser local time zone.
GOOD TO KNOW
Common questions
Can I subtract days?
Yes. Use a negative whole number.
Are fractional days accepted?
No. This tool applies whole calendar days only.