Days calculator — count the days between two dates, or add days to one

Both, depending on the question. There are 30 days *between* them, because you are measuring the gap and the last day has not finished. There are 31 days *from* 1 to 31 January inclusive, because you are counting the dates themselves. This tool makes you choose with the "count the last day too" switch, and then writes the range it used underneath the answer in words, so there is never any doubt which one you are looking at. As a rule of thumb: gaps, ages and interest periods exclude the end day; leave, notice periods, prison sentences and hotel stays include it.

Yes, including the century rule that most people forget. A year is a leap year if it divides by 4, except century years, which must divide by 400 — so 2000 was a leap year and 1900 was not, and 2100 will not be. The arithmetic here is done on the real Gregorian calendar rather than on an average year length, so 1 January 2024 to 1 January 2025 comes back as 366 days, and 2025 to 2026 as 365.

It removes the problem instead of correcting for it. Dates here are stored as three numbers — year, month, day — and adding a day means adding one to a day count, never adding 86,400,000 milliseconds to a timestamp. On the morning a clock shifts, a day is 23 or 25 hours long, and calculators built on timestamps land on the wrong date for millions of people twice a year. Nothing here has a clock in it, so there is nothing for daylight saving to move. The "total hours" figure is therefore the calendar days multiplied by 24, which is what people mean by hours between two dates.

Because 31 February does not exist, and the accepted answer is to clamp to the last day of the target month. This is what Excel’s EDATE does, what date libraries do, and what contracts assume when they say "one month from signing". It has one consequence worth knowing: the operation is not reversible. 31 January plus one month is 28 February, but 28 February minus one month is 28 January. That is not a rounding error — it is what happens when a month is shorter than the day number you started on.

Whole months are counted first, then whatever is left over in days — never by dividing the day count by 30.44. To get it right at the end of a month, the calculator takes the number of months, adds them back to the start date with the end-of-month clamp above, and checks the result has not overshot the target. So 31 January to 29 February 2024 is exactly 1 month and 0 days, while 31 January to 28 February is 0 months and 28 days. Naive implementations report one of those two wrongly.

Every calendar day in the range you selected, minus the days you marked as your weekend, minus any holidays you added that do not already fall on a weekend. That last clause matters: a public holiday landing on a Saturday is listed in the tool but not deducted again, because the Saturday was already off. Deducting it twice is the single most common bug in working-day calculators, and it fails quietly — the answer is only ever one or two days low, which nobody notices until a deadline is missed.

Yes. Several Malaysian states — Kelantan, Terengganu, Kedah and Johor — take Friday and Saturday, and plenty of workplaces take Sunday only or work every day. Each of the seven days is a switch, with presets for the common patterns. The working-day answer, and the working-day mode in the add-or-subtract tab, both follow whatever you set.

No, and that is deliberate rather than unfinished. Public holidays differ by country, by state and by year, and several are declared only weeks ahead or moved when they fall on a Sunday — a built-in list would be wrong for most visitors and, worse, would look authoritative while being wrong. You add the dates that actually apply to you, and the tool tells you which of them it counted.

Nothing you type is uploaded. The whole calculator is JavaScript running in this tab, with no server involved at any point, so it also works with the connection off. Your weekend setting and your holiday list are the only things kept, and they are kept in your own browser’s local storage so you do not have to retype the same public holidays on every visit. Clear your site data and they are gone. Like the rest of this site, the page itself serves ads, which is explained on the privacy page.

The week of the year under ISO-8601, the standard used by payroll, logistics and most of Europe. Weeks start on Monday, and week 1 is the week containing the first Thursday of January — which means a date in early January can belong to week 52 or 53 of the *previous* year. The tool shows the owning year alongside the week for exactly that reason: "week 53" on its own is ambiguous on 1 January.

From year 1 to year 9999, and it stays correct across the whole range because it uses the proleptic Gregorian calendar — the modern calendar projected backwards. One caveat for historians: countries switched to the Gregorian calendar at different times between 1582 and 1923, so for dates before then the answer is arithmetically right but may not match a contemporary document.