Date Calculator
Dates in, answers out.
Runs on your device
At a glance
- Input:
- Numbers you enter
- Processing:
- Runs locally in your browser
- Privacy:
- Your files stay on your device — nothing is uploaded to a server
About this tool
Two dependable date operations: project deadlines forward/backward with calendar-accurate arithmetic, and measure spans in years, months, weeks and days.
How to use it
- Pick Add/Subtract or Duration mode.
- Enter the base date and offset — or two dates.
- Get calendar-accurate results immediately.
Frequently asked questions
How does adding months work across month lengths?
Calendar-clamped, like most legal counting: Jan 31 + 1 month lands on Feb 28/29, since Feb 31 doesn't exist. Each convention note is displayed.
Is the end date included in durations?
Durations report the difference (end exclusive) but display both interpretations — useful for rental days vs nights style questions.
Do you store entered dates?
Never. Everything is computed and forgotten locally.