Tool
Date Calculator
Compute the number of days between two dates or add a number of days to a date.
Try it
This tool runs entirely in your browser. Nothing you type or paste is sent anywhere.
2026-01-01 to 2026-03-01 is 59 day(s).
How it works
- Parsed both dates as UTC instants.
- Subtracted the start from the end and divided by 86,400,000 ms per day.
- Rounded to the nearest whole day.
days = (end - start) / 86_400_000Usage
- Enter a start date.
- Enter an end date to measure a difference, or a number of days to add.
- Read the result.
Examples
Difference in days
{
"start": "2026-01-01",
"end": "2026-03-01"
}Add 30 days
{
"start": "2026-01-01",
"addDays": 30
}Limitations
Difference vs. duration
A difference answers 'how many whole days elapsed?'. A duration in months or years depends on where you start, which is why this tool reports days and weeks explicitly rather than guessing calendar units.
Frequently asked questions
- Does it handle leap years?
- Yes. The calculation is calendar-based and uses the real length of each month.