Date Arithmetic
Add or subtract time units from a date while keeping everything private and in-browser.
Start Date
Date Math
How it works
Frequently Asked Questions
What is date arithmetic?
Date arithmetic is the calculation of adding or subtracting specific units of time (such as days, weeks, months, or years) to or from a starting calendar date to determine an exact future or past date.
How does adding months handle dates with different days (like January 31st)?
When adding or subtracting months, if the target month has fewer days than the starting day (for example, adding one month to January 31st), the calculator clamps the result to the last valid day of that target month (February 28th, or February 29th in a leap year).
Can I perform date arithmetic in UTC instead of local time?
Yes, use the 'Time Standard' dropdown to switch between your local browser timezone and UTC. Calculating in UTC avoids unexpected time jumps caused by Daylight Saving Time (DST) transitions.
How do I calculate a past date?
Set the Operation dropdown to 'Subtract' and enter the amount of days, weeks, months, or years you wish to count backward from the selected date.
What output formats are provided?
The calculator instantly outputs four convenient formats: a formatted local date string, UTC string, standard ISO 8601 timestamp, and numeric Unix epoch timestamp.
