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Add or Subtract Days from a Date

Add or subtract days, weeks, months, or years from any date and instantly see the result — completely free, with no account required. Useful for contract deadlines, figuring out "45 days from today," due dates, return windows, or planning ahead by weeks, months, or years. Everything runs right in your browser; nothing is sent to a server.

Start Date
Direction
Amount of Time

How to Add or Subtract Time From a Date

  1. 1 Pick your start date. It defaults to today, but you can set the month, day, and year dropdowns to any date — past or future.
  2. 2 Choose Add or Subtract. Adding moves forward from your start date; subtracting moves backward.
  3. 3 Enter a quantity and unit. For example, 45 Days, 6 Weeks, 3 Months, or 10 Years.
  4. 4 Click "Calculate." You'll instantly see the resulting date, its day of the week, and the total number of days between it and your start date.

How Month and Year Math Handles Edge Cases

Adding days or weeks to a date is simple arithmetic — but months and years are trickier, because not every month has the same number of days and not every year is a leap year. Here's how this calculator handles the tricky cases:

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End-of-month overflow

Naively adding one month to January 31 with JavaScript's built-in date math produces March 2nd or 3rd, because there's no February 31st, so the extra days silently roll into the next month. This calculator checks whether the target month actually has that many days, and if not, clamps the result to the last valid day of that month — so January 31 plus one month correctly lands on February 28 (or 29 in a leap year), not March.

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Leap years and February 29

The same clamping logic applies to years. If you add one year to February 29 of a leap year, the following year almost certainly isn't a leap year, so there's no February 29 to land on. The calculator clamps that result to February 28. It correctly follows the standard Gregorian leap-year rule: every 4th year is a leap year, except centuries not divisible by 400 (so 2000 was a leap year, but 1900 and 2100 are not).

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Days and weeks never need clamping

Because days and weeks are fixed-length units, adding or subtracting them naturally rolls over month and year boundaries with no ambiguity — 10 days after December 28 is simply January 7 of the next year. Clamping only comes into play with the variable-length units: months and years.

Frequently Asked Questions

Is this date calculator really free?

Yes — completely free, with no account, no sign-up, and no limit on how many times you use it. There's nothing to install and nothing hidden behind a paywall.

What happens when adding a month lands on a day that doesn't exist?

For example, January 31 plus one month can't land on February 31, since February only has 28 or 29 days. Instead of rolling over into March, this tool clamps the result to the last day of the target month — so you'll get February 28 (or February 29 in a leap year). When this happens, the results panel shows a short note explaining the adjustment.

Does it account for leap years?

Yes. The calculator uses JavaScript's native date engine, which correctly follows the Gregorian leap-year rule (every 4th year is a leap year, except century years not divisible by 400). This affects both how many days are in February and how day-of-week and day-count results are calculated across leap years.

Can I subtract time to go backward as well as add it forward?

Yes. Choose "Subtract" and the tool will calculate the date that many days, weeks, months, or years before your start date, using the same overflow and leap-year handling described above.

How far into the future or past can I calculate?

The start date dropdowns cover years from 1900 through roughly 50 years from now, which is enough range for historical dates, contract terms, and long-range planning like retirement dates. You can also enter large quantities (for example, 500 weeks) to project well beyond that window from any start date.

Does the day-of-week result account for calendar reform?

This tool uses the standard, modern Gregorian calendar for all calculations, which is the calendar in official and everyday use worldwide today. It does not model the historical transition from the Julian calendar (which happened at different times in different countries between the 1500s and 1900s), so it isn't intended for calculating day-of-week on dates before your country's Gregorian adoption.

Is my data sent anywhere?

No. All calculations happen entirely in your browser using JavaScript — nothing is transmitted to a server. Your dates stay private on your device.

Why does "days from your starting date" not always match the quantity I entered?

If you add months or years, the total day count depends on exactly which months are spanned, since months vary from 28 to 31 days. For example, 1 month from January 1 spans 31 days, but 1 month from April 1 spans only 30. The "That's N days from your starting date" line always reflects the true calendar distance, not a rough estimate.

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