How Date Calculator Works
For days and weeks, the tool simply moves forward or backward that many calendar days from your start date. For months and years, it shifts the calendar month first and only then checks the day of month — if your start date doesn't exist in the target month (like 31 January plus one month), it clamps to that month's last valid day (28 or 29 February) instead of overflowing into the next month.
How to Use This Tool
- Enter your starting date.
- Choose whether to add or subtract, then enter an amount and pick a unit — days, weeks, months or years.
- Select Calculate Date to see the resulting date, its day of the week, and how many calendar days separate the two dates.
Example
Adding 1 month to Saturday, 31 January 2026 lands on Saturday, 28 February 2026 — since 2026 isn't a leap year, February only has 28 days, so the result is clamped there instead of rolling into March.
Helpful Tips
- When adding months or years lands on a day that doesn't exist in the target month (like 29 February in a non-leap year), the tool clamps to the last valid day instead of spilling into the next month.
- Use Subtract to find a date a certain amount of time in the past, such as "90 days before today".
- The day-of-week shown in the result is calculated from the real calendar, so it's accurate for any date, past or future.
Frequently Asked Questions
What happens if adding a month lands on a day that doesn't exist?
The result is clamped to the last valid day of that month. For example, 31 January plus one month gives 28 February (or 29 in a leap year), not 2 or 3 March.
Can I subtract time instead of adding it?
Yes, choose "Subtract" from the operation dropdown to move backward from your start date instead of forward.
Does this account for leap years automatically?
Yes. Month and year calculations always check the real number of days in the target month, including February in leap years.
What's the difference between adding weeks and adding days?
Adding 1 week is the same as adding 7 days — it's just a more convenient unit when you're thinking in whole weeks.
This tool runs entirely in your browser. Your input is not uploaded to any server.