January 1, 2026 to December 31, 2026 is 364 days, because the count measures the full days between the two dates rather than counting both endpoints.
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A contract that says 30 days and one that says one month can point to different dates, sometimes by a day or two, sometimes by more. Thirty days is a fixed count. A calendar month runs anywhere from 28 to 31 days depending on which month you land in. This tool counts days; for a month-based deadline, count to the same date number in the later month instead.
Every date here becomes a single number first, a count of days from a fixed reference point, so subtracting one from the other gives the gap directly without ever touching "how many days does this month have" as a separate step. That's what quietly handles the awkward part of date arithmetic: months running 28 to 31 days, and February picking up an extra one in leap years.
| Span | Days | Notes |
|---|---|---|
| One common year | 365 | February has 28 days |
| One leap year | 366 | February has 29 days |
| Jan 1 to Dec 31 (same year) | 364 | nights between, not both ends |
| One week | 7 | |
| Four weeks | 28 | not the same as one month |
A year is a leap year if it divides evenly by 4, except century years, which also have to divide evenly by 400. So 2000 was a leap year, 1900 was not, and 2024 was. 2026 is an ordinary 365-day year with a 28-day February. Because the tool works from real calendar dates rather than a fixed 365-day assumption, any leap day sitting inside your range gets counted automatically.
Add/subtract mode exists for deadlines: a 30-day notice period starting January 15 lands on February 14, rolling across whatever month boundary falls in between without you having to count on your fingers. Enter a negative number to move backward instead, useful for working out when something must have started given a fixed deadline. The result always lands on a real calendar date, weekends included; for a count that skips weekends and holidays, the business days calculator is the right tool.
Run March 10, 2026 against July 18, 2026 and the tool reports 130 days. Below that headline number it shows 18 weeks 4 days, which is just 130 split by sevens, and 4.3 months. That last figure deserves a word of explanation, because no calendar has a 30.44-day month: the tool divides by 30.44 because that is the average month length when you spread 365.25 days across 12 months. It is a planning approximation, deliberately labeled as months rather than presented as an exact count. For anything contractual, trust the day count; the month figure is there to give the number scale, not to sign a lease with.
Add mode earns its keep on waiting periods. A 90-day probationary period starting January 15, 2026 runs out on Wednesday, April 15, and the tool crosses the 16 remaining January days, all of February, and all of March without you tracking any of it. Benefits paperwork leans on fixed day counts constantly, 30-day notice windows, 60-day election periods, and the failure mode is always the same: someone counts "three months" on their fingers when the document says 90 days, and lands a day or two off. If the paperwork names a number of days, feed that exact number in here and let the calendar be the calendar.
Enter the dates in either order; the tool takes the absolute difference, so a swapped start and end cannot produce a negative day count or a silent error. That makes it safe for the backward question too: given a deadline, when did the clock most likely start? Subtracting a known day count from a known end date is the same arithmetic run in reverse, and add mode with a negative number does exactly that.
Sources: timeanddate.com date duration reference, U.S. Naval Observatory Astronomical Applications.
Last updated July 18, 2026.
No, and the gap can matter. Thirty days is a fixed count; one calendar month can be 28 to 31 days depending on which month it is. If the text says days, count days with this tool; if it says months, count to the same date number in the later month instead.
This tool counts the nights between the two dates, meaning it counts one endpoint but not both. If your situation requires counting both calendar dates as full days, add one to the result.
Switch to add/subtract mode, enter the deadline as the start date, and enter -90 in the days field. The result is the date 90 days earlier.
Because January 1 to December 31 of the same common year is 364 nights apart, not 365; the 365th day is the start date itself. Counting both endpoints would add the missing day back.
Yes, every calendar day counts equally here. If you need a count that skips Saturdays, Sundays and optionally holidays, use the business days calculator instead.