Dates and Days

Date calculator

Days between two dates, or a date a number of days out

Both readings of "days between" are offered and the answer always says which one it used. Every figure is computed here in your browser.

Days— Calendar days— Weekend days— Holidays removed— Convention—
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Which reading of "days between" you want

Two people asking how many days lie between the 1st and the 8th can reasonably want different answers. Seven is the gap: the number of nights, the number you add to one date to reach the other. Eight is the count of dates involved, which is what the question means when it is really "how long is my trip" and both ends are days you are somewhere.

This page defaults to the gap and offers the other with a checkbox, and the sentence under the answer always names which one it used. A calculator that quietly picks one is right half the time and never tells you which half.

Why the arithmetic runs in whole days

A date here is a year, a month and a day, not a moment in time. Every calculation converts to midnight UTC, does integer arithmetic on whole days, and converts back. That matters twice a year: local-time arithmetic across a daylight-saving change gains or loses an hour, and an hour is enough to land an answer on the wrong date. The one place local time is used is the word "today", because that is a question about where you are standing. The rules are written out in full, with the statute they come from.

Working days instead of calendar days

If the count you need has weekends and public holidays taken out — the shape most shipping windows and legal deadlines use — the business days calculator does that, and lists every day it removed so you can check it rather than trust it.

Every calculator on this site

Ten instruments, all computed in your browser, all showing the convention they applied.

Questions

Is it seven days or eight days between the 1st and the 8th?
Both answers are defensible and they answer different questions. Seven is the gap: the number of nights, and the number you add to the first date to reach the second. Eight is the count of dates involved, which is what you want when the question is really how long a trip or a stay lasts and both ends are days you are somewhere. This page gives the gap by default, offers the other with the “count both endpoints” box, and the line under the answer always names which one it used.
Does it handle leap years and the 29th of February?
Yes, and it uses the full rule rather than the divisible-by-four shorthand. A year is a leap year when it divides by four, except century years, which must divide by four hundred. So 2024 and 2028 have a 29 February, 2100 does not, and 2000 did. Asking for 29 February in a year that has none is refused as an impossible date rather than quietly moved to 1 March.
Why does the answer not change when the clocks go forward?
Because the arithmetic never uses a clock. A date here is a year, a month and a day, and every calculation happens on whole days in UTC before being converted back. Daylight saving moves an instant by an hour, and an hour is enough to push a naive calculation onto the wrong date twice a year — which is the single most common way a date calculator is quietly wrong.
Does anything I type here get uploaded?
No, and not as a matter of policy. This page is a static file and a script your browser downloads once; there is no server behind it to receive anything. The dates you enter are read by the script in your own browser and the answer is written back into the same page. Nothing is sent, nothing is stored, and no analytics or third-party script runs here.
Can it add months or years rather than days?
Yes, on the days-from-today page, which takes days, weeks, months or years. Adding a month is genuinely ambiguous rather than difficult: one month after 31 January is either 28 February, 2 March, or an error, depending on which convention you follow, and every one of those is used somewhere in practice. So that page asks you which. Clamp gives 28 February; overflow gives 2 March; strict refuses and says the 31st does not occur in the target month. Whichever you pick is named underneath the answer, because a date arrived at by an unstated rule is a number you cannot check.