Date Duration Calculator
Days, weeks, months, and years between two dates — counted both ways, so you can see whether the answer you want includes the first day and the last. Weekdays and weekend days too.
Two dates
The day the count starts from — check-in, the day a contract is signed, the first day of a project.
Check-out, the deadline, the last day. It may be the same day as the start; it may not be earlier.
From Thursday, January 1, 2026 to Thursday, December 31, 2026. That is 364 counting one endpoint — the elapsed span, and what a hotel bills as nights — or 365 counting both the first day and the last.
- Days, counting one endpoint
- 364
- Days, counting both endpoints
- 365
- Calendar breakdown
- 0 years, 11 months, 30 days
- Whole months
- 11
- Whole weeks
- 52 weeks
- Weekdays, Monday to Friday
- 261
- Weekend days
- 104
| Way of counting | Days | Use it for |
|---|---|---|
| One endpoint (exclusive) | 364 | Hotel nights, interest accrued, elapsed time, the gap between two events |
| Both endpoints (inclusive) | 365 | Days of a stay, days a permit or a visa covers, days someone was on site, leave taken |
- Weekday and weekend counts include both endpoints, so they always add up to the inclusive figure of 365.
- Public holidays are not deducted — a weekday here is any Monday through Friday, wherever you are.
- The month figure counts calendar months, so 31 January to 1 March is one month and one day rather than 0.95 months.
Four or five: why “days between” has two right answers
Ask how many days there are from the 1st to the 5th and you will get 4 from one person and 5 from another, and neither has made a mistake. Subtracting the dates counts one endpoint and gives the elapsed span: 4. Counting the days on a wall calendar counts both and gives the size of the range: 5. A hotel bills the first figure as nights and prints the second on the confirmation as a five-day stay, for exactly the same booking.
exclusive = end − start • inclusive = end − start + 1- Exclusive
- Nights booked, interest accrued, age, elapsed time, notice served, the gap between two events
- Inclusive
- Days of a stay, days a permit or visa covers, days on site, leave taken, days a festival runs
- Rule of thumb
- If both endpoints are days that something happened on, count inclusively. If the endpoints are the moments the span runs between, count exclusively
The rest of the tool follows from that split. The calendar breakdown, the month total, and the week total are elapsed durations, so they are exclusive by construction — at the moment you start, nothing has elapsed. The weekday and weekend counts are the opposite kind of number: they count days that are in the range, so both endpoints belong to it. That is why weekdays plus weekend days always equals the inclusive figure, never the exclusive one. The identity is a deliberate check — if those two rows do not sum to the inclusive count, something is wrong.
Months are counted the way you subtract in columns: years, then months, then days, borrowing when a column goes negative. The borrow takes the previous month’s real length — 28, 29, 30, or 31 — never a 30.44-day average. Borrowing a fixed length is the most common bug in date calculators, and it shows up as an answer that is a day or two off for about a third of the year. Both dates are read as ISO 8601 calendar dates and compared at midnight UTC, which has no daylight saving, so every day is exactly 86,400 seconds and the day count is exact integer arithmetic.
1 January 2026 to 31 December 2026, carried all the way through
Subtract the timestamps and you get 364 days elapsed — 2026 is a common year, and 1 January to 31 December is a year minus a day. Count both endpoints and you get 365, which is the number of days 2026 contains. Divide the 364 by seven: 52 weeks and 0 days, and no remainder, which happens because the year opens and closes on a Thursday.
Now the calendar columns. Years: 2026 − 2026 = 0. Months: 12 − 1 = 11. Days: 31 − 1 = 30. Nothing goes negative, so nothing is borrowed, and the breakdown is 0 years, 11 months, and 30 days — eleven whole calendar months. And because the year begins and ends on a Thursday it contains exactly 52 whole weekends: 104 weekend days and 261 weekdays, which add back up to the inclusive 365 rather than the exclusive 364.
A shorter span shows the split at a size you can check by eye. From Thursday 1 January to Monday 5 January 2026: 4 nights, 5 days, and within those five days a Saturday and a Sunday — 3 weekdays and 2 weekend days. Book a hotel for that span and the invoice says four nights while the itinerary says five days, and both documents are describing the same trip.
One more, for the month arithmetic. From 31 January to 1 March 2026is 29 elapsed days. The day column is 1 − 31 = −30, so a month is borrowed at February’s actual 28 days — not 30, and certainly not 30.44 — giving 1 month and 1 day. Read that as 31 January plus one month clamping to 28 February, and 28 February plus one day being 1 March. Divide instead and 29 ÷ 30.436875 = 0.95 months, which says a month has not yet passed. Neither is a rounding error; they are answers to different questions.
What this calculator assumes
- Whole calendar days only. Times of day, hours, and minutes are not part of the calculation, so a duration is the same whatever time you set out.
- Both dates are compared in UTC, which has no daylight saving. Your device’s time zone never changes an answer here.
- Weekday and weekend counts include both endpoints, and always sum to the inclusive figure. Public holidays are not deducted — that needs a country, and often a state, so it belongs to the business-days calculator rather than to this one.
- A weekend means Saturday and Sunday. In countries where the working week runs Sunday to Thursday, the two figures are the right count of the wrong days.
- Months are counted from the calendar, never from a 30.44-day average, and the borrow uses the previous month’s real length.
- Dates from 1583 onward only. The Gregorian calendar began in October 1582, and answering confidently for earlier dates would mean applying its rules to a period that did not use them.
- The end date may not be earlier than the start date. The tool will not quietly swap them, because which one is which is what makes the inclusive and exclusive figures mean anything.
Date duration FAQ
How many days are there from the 1st to the 5th — four or five?
Both, and which one is right depends on what you are counting. Counting one endpoint gives 4: that is the elapsed span, and it is what a hotel bills as nights, what interest accrues over, and what a court means by a period that starts the day after an event. Counting both endpoints gives 5: that is the size of the range, and it is what you want for days of a stay, days a permit or a visa covers, or days someone was on site. This calculator shows both figures side by side and labels them, because a single number here is a number you cannot check.
Why does this say 364 days in 2026 when a year has 365?
Because 1 January to 31 December is not a whole year — it is a year minus a day. The 364 is the elapsed count from the first date to the last; the inclusive count, which is the number of days the year contains, is 365. Add one day to the end date, 1 January 2026 to 1 January 2027, and the elapsed count becomes 365 too. If the two figures in a duration ever surprise you, this is almost always why.
How long is a 30-day notice period, and when does it end?
In United States federal practice, Rule 6(a) of the Federal Rules of Civil Procedure excludes the day of the event that triggers the period and includes the last day — the exclusive convention. A 30-day period triggered on 1 April therefore ends on 1 May, not 30 April. Rule 6(a) also rolls a deadline that lands on a Saturday, Sunday, or legal holiday forward to the next business day, which this calculator does not do. Your own contract, lease, or jurisdiction may count differently, and the wording is usually the place to check: “within 30 days of” and “30 days from” are frequently read as excluding the trigger day, while “for 30 days beginning on” includes it.
How many weekdays are between two dates?
The weekday row counts every Monday through Friday in the range, with both endpoints included — so the weekday and weekend figures always add up to the inclusive day count. Public holidays are not deducted, because a holiday calendar depends on the country, and often the state or province, that you are asking about. From 1 January to 31 December 2026 there are 261 weekdays and 104 weekend days, adding up to the 365 days the year contains.
Why is 31 January to 1 March one month and one day rather than 0.95 months?
Because months are counted from the calendar rather than divided out of a total. The Gregorian calendar repeats every 400 years, which is exactly 146,097 days, so the average month is 146,097 ÷ 4,800 = 30.436875 days — and 29 ÷ 30.436875 is 0.95, which says a month has not passed. By the calendar it has: 31 January plus one month is 28 February, and one more day is 1 March. Neither figure is wrong; they answer different questions, and calendars, leases, and anniversaries are written in the calendar one.
Does my time zone change the answer?
No. Both dates are treated as plain calendar dates and compared at midnight UTC, which has no daylight saving, so a day is always exactly 24 hours and no result shifts because a clock went forward. Times of day are not part of the calculation at all — a duration from the 1st to the 5th is the same whether you set out at dawn or at midnight.
Sources and review notes
- ISO 8601-1:2019 — the standard that defines the
YYYY-MM-DDcalendar date and the rules for durations between two of them - Federal Rules of Civil Procedure, Rule 6(a) (Cornell Legal Information Institute) — the exclusive convention in United States federal deadlines: exclude the triggering day, include the last day
- US Naval Observatory, Astronomical Applications — the Gregorian leap-year rule and the 400-year, 146,097-day cycle the 30.436875-day average month comes from
There is no dataset behind this page to go stale. The leap-year rule has been fixed since 1582 and the month lengths since Julius Caesar; what changes between one reader and the next is only which of the two day counts they needed.