Date & Time Tools
Date Calculator
Add or subtract years, months, weeks and days from a calendar date.
Starting date
Resulting date
Calendar date
2026-02-15
About this tool
Adding calendar units uses the JavaScript local date setters: years, then months, then weeks×7 + days. Month overflow follows the host calendar (31 Jan + 1 month can become 2–3 Mar).
How to use
- Pick a start date.
- Choose add or subtract.
- Enter years, months, weeks and days.
Formula and methodology
Date#setFullYear, setMonth, then setDate with week and day offsets.
Worked example
1 January 2026 plus 1 month is 1 February 2026.
Frequently asked questions
Why did 31 January plus one month skip February?+
February has fewer than 31 days. The extra days roll into March. That is standard calendar overflow.
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