Date Calculator

How to use

On the "Days between dates" tab, pick a start and end date to see the number of days, along with the count in weeks and months. On the "Add or subtract days" tab, enter a start date and a number of days, then choose "after" or "before" to get the resulting date (it defaults to 100 days from today).

It fits a lot of uses: counting day 100 or day 1000 of a relationship or a baby's life, a countdown to an event, a project deadline worked backwards, or hospital and medication day counts. When you want to count something as "day 1," tick "count the first day."

All counting is done on a timezone-independent calendar basis, so you get the same answer regardless of your device's region settings or where you access it from.

How the counting works

Including or excluding the first day shifts the answer by one. Many legal and practical periods are counted from the next day, excluding the first day — contracts, expiry dates, and official deadlines usually work this way, and that is the default here. By contrast, anniversaries and "day N" counts often treat the first day as day one (counting both ends). A single checkbox switches between the two. For anything legally binding, confirm the rule with an official source.

The number of months can differ between tools. This calculator counts in calendar months: January 31 to February 28, for example, is shown as "1 month" (a non-existent February 31 is clamped to the last day of the month). Tools that divide by a flat "30 days per month" can land a day or two apart. Neither is wrong — it is a difference of definition, so it helps to know this tool uses calendar months with end-of-month clamping. Weeks and months are based on the first-day-excluded count.

FAQ

What date is 100 days from today?

Open the "Add or subtract days" tab — it already defaults to 100 days from today, so the answer shows immediately. Change the number for 1000 days or any other count, and choose "before" to get the date 100 days ago instead.

Should I include or exclude the first day?

For periods like contract terms, expiry dates, and official deadlines, excluding the first day is the usual rule. For anniversaries and "day N" counts, including the first day (counting both ends) is more common. For anything legally binding, confirm the exact rule with an official source or professional.

Why is the "months and days" figure one day off from another site?

Because the definition of a month differs. This tool counts calendar months (January 31 to February 28 is one month, with end-of-month clamping). Tools that use a flat 30-day month can differ by a day or two, but neither result is wrong.

Can it count business days (excluding weekends and holidays)?

This tool counts calendar days (every day). It does not exclude weekends or public holidays. If you need a business-day count, use the separate Business Days tool.