Days Between Dates

How the day count works (and the off-by-one trap)

The number of days between two dates is the later date minus the earlier one, counted in whole days. By default this calculator does not include the end date, so it answers "how many full days have passed." January 1 to January 31 is 30 days, because the 1st itself is the starting point and only 30 full days have elapsed by the 31st.

That default is exactly right for questions like "how long ago" or "how much time has passed." But plenty of real situations count both the first and last day, a hotel stay from the 1st to the 3rd is two nights but three days, and a vacation Monday to Friday is five days, not four. That is what the include the end date checkbox is for: it adds one day to the total. On the same January example it turns 30 days into 31.

So the same pair of dates can legitimately be reported as two different numbers. The tool shows both so you can pick the convention your situation needs rather than guessing which one is "correct." Dates are entered in the YYYY-MM-DD form defined by the ISO 8601 standard, which sorts correctly and avoids month/day confusion.

Worked example: a 30-day return window

You buy a laptop on June 1 and the store allows returns within 30 days. When does the window close?

• If the store counts from the next day (the common retail rule), day 1 is June 2, and day 30 is July 1.
• If the store counts the purchase day as day 1, day 30 is June 30.

Either way the arithmetic is the same subtraction you see here: June 1 to July 1 is 30 days, and June 1 to June 30 is 29 days. The disagreement is purely about whether the start day counts. When a policy matters, find the phrase "from the date of purchase" or "excluding the date of purchase" in the fine print, that one word decides whether you have until June 30 or July 1.

The same span in weeks, hours and minutes

Once you have the day count, every other unit is a fixed multiplication. This table shows a few common spans.

Notice 90 days is 12 weeks and 6 days, not a clean 13 weeks, that is why "90-day" and "13-week" plans are not the same length. If you need a round number of weeks, 91 days is exactly 13 weeks. To cross-check a result, timeanddate's duration calculator uses the same day-count convention.

Calendar months vs. dividing the days by 30

People often take the day count and divide by 30 to get "months." That gives an average, not a real calendar count. Calendar months have 28, 29, 30 or 31 days, so the honest way to count months is to walk the calendar one month at a time.

Example: January 15 to March 15 is exactly two months, even though it is 59 days in a common year and 60 days in a leap year. Divide those same 59 days by 30 and you get 1.97, close, but wrong, and wrong in a way that compounds over long spans. This calculator walks the calendar, so a span that lands on the same day-of-month in a later month reads as a whole number of months, exactly as a person would say it.

Leap years: when February has 29 days

Under the Gregorian calendar, a year is a leap year if it is divisible by 4, except for century years, which must be divisible by 400. So 2024 and 2028 are leap years, 2026 is not, and 1900 was not a leap year while 2000 was. The extra day is February 29.

For a day counter, the practical effect is that any span crossing February 29 is one day longer in a leap year. February 28 to March 1 is 1 day in a common year but 2 days in a leap year, because the 29th sits between them. The calculator uses your browser's built-in calendar, so it handles this automatically, but if you are checking a hand calculation, this is the single most common place a total goes wrong by exactly one. The full Gregorian rule is explained by the US Naval Observatory.

Business days vs calendar days

This tool counts calendar days, and it also reports how many of them are weekdays (Monday to Friday). It does not subtract public holidays. So a January 1 to January 31 span in 2026 is 30 calendar days, of which 21 are weekdays after the start date is excluded.

If your deadline is defined in business days, "payment due within 30 business days", you need the weekend days and the federal holidays removed. That is a different calculation, and there is a dedicated tool for it on this site. Use this page when you want elapsed calendar time; use the business days calculator when weekends and holidays are excluded.

Where people use a day count

A date-difference calculator shows up in more places than you would expect:

• Deadlines and notice periods, how many days until a contract clause triggers, or how much notice you must give.
• Warranties and return windows, is the 30-day window still open today?
• Billing and interest, the number of days between two statement dates drives prorated charges.
• Travel and events, countdowns, trip lengths, hotel nights.
• Ages and anniversaries, the exact days between two birthdays or a milestone date.

In every one of these, the one decision that changes the answer is whether the end date is included. Pick the convention that matches the rule you are applying, and the rest is simple subtraction.

Counting a notice period or a subscription renewal

A common use of a day counter is working out a notice period. If a lease requires "30 days' written notice" and you give notice on the 15th, the earliest you can leave depends on whether the 30 days run from the notice date or from the day after.

• Notice given March 15, counted from the next day: the 30th day is April 14.
• Counted from the notice date itself: the 30th day is April 13.

Subscriptions behave the same way, with one extra wrinkle. A monthly plan started on the 31st is awkward, because not every month has a 31st, most systems roll the renewal to the last day of February and then back to the 31st in longer months. If you are trying to cancel before a renewal, look up the exact renewal date the provider lists rather than assuming "one month" from the sign-up day, and leave a couple of days of buffer for time zones and payment processing. When money or a deadline is on the line, treat the day count as a guide and confirm the date in writing.