Date Calculator
Count the exact number of days between two dates, or add and subtract days to find a deadline — with the weekday included.
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Last updated: September 9, 2026 · Formulas verified by automated tests that block every release. Editorial review dates are shown in the sources block above.
Two calculators in one
Days between dates answers questions like "how many days until my deadline" or "how long was the project" and also expresses the result in weeks and days.Add or subtract days works the other way around: it takes a start date and a duration and gives you the exact calendar date — including the day of the week, which is often what actually matters.
The off-by-one problem, and how to never lose to it
Ask two people how many days lie between March 1 and March 5. One says four, the other five, and both are right — they are answering different questions. Four is the elapsed count: the gaps you cross. Five counts the days themselves, March 1 through March 5. Engineers call the trap the fence-post error: a ten-metre fence with posts every metre needs eleven posts, not ten. It has voided legal filings, missed statutory deadlines and misquoted interest.
Which is why this page shows both numbers at once rather than hiding one behind a toggle you must set before you know the answer. And you rarely need to guess: the wording of the rule almost always picks for you.
| If the rule says… | Count | Because |
|---|---|---|
| "between these dates" | Elapsed | The endpoints frame the gap, they aren't part of it |
| "through", "including", "up to and including" | Both dates count | The final day is an active day of the period |
| "within 30 days of…" | Usually both — check the wording | Deadlines commonly count the day the clock starts |
| "90 days in any 180-day period" (visas) | Both dates count | Arrival and departure days each count as days present |
| Hotel nights | Elapsed | You pay for nights slept, not calendar days touched |
| "7-day course" (medication) | Both dates count | Monday to Sunday is seven doses, not eight |
Two habits worth keeping. When a number matters, state the convention beside it — "14 days, both dates counted" ends an argument before it starts. And when the count comes from a contract, court order or immigration rule, read the exact phrase rather than assuming: jurisdictions differ on whether the day an event happens counts at all, so the safest source is the document itself or the authority that issued it, not a general calculator — including this one.
Weekdays, working days and the deadline that lands on a Saturday
The result above also shows business days (Monday to Friday) and the weekday your end date falls on, because both change what a deadline actually means. Thirty calendar days is roughly twenty-two working ones — a third of the time you thought you had, if the work happens on weekdays. And a due date landing on a Saturday usually means the real deadline is the Friday before, not the Monday after; many contracts say the opposite, which is precisely why it is worth checking rather than assuming. Public holidays are not deducted here, since they differ by country and region — if your deadline is tight, count them yourself against your local calendar. For a pace-per-day view of a deadline, thedeadline pace calculator divides the remaining work across the remaining working days.
Typical scenarios
- Visa rules: the date 90 days after arrival.
- Payments and contracts: a due date 30 or 60 days after the invoice.
- Events and trips: days remaining until a wedding, exam or departure.
- Health: days since a treatment started or between appointments.
All date math happens locally in your browser.
Frequently asked questions
Should I count both the start and end date?
It depends on the wording, not on preference. "Between two dates" means the elapsed count; "through", "including" or "up to and including" means both dates count. Deadlines phrased "within 30 days" usually count the day the clock starts. This calculator shows both numbers so you can match whichever your rule uses — and if a document is ambiguous, ask the issuer rather than guessing, because the difference is exactly one day and that is where disputes live.
Why do two calculators give different answers for the same dates?
Almost always because one counts the endpoints and the other does not — the classic off-by-one, or fence-post error. A ten-metre fence with posts every metre needs eleven posts. Neither answer is a bug; they answer different questions. That is why both counts are shown here side by side rather than one being chosen for you.
How many business days are between two dates?
The result shows it: every Monday through Friday in the span, weekends excluded. Public holidays are not deducted, because they differ by country, region and sometimes employer — check yours against a local calendar if the deadline is tight. As a rule of thumb, 30 calendar days is about 22 working days.
Does the calculator handle leap years and different month lengths?
Yes. It works on real calendar dates rather than an approximation, so February 29 is counted when it falls inside the range and month lengths are whatever the calendar says. A span crossing February 29 is genuinely one day longer than the same span in an ordinary year.
How are days between two dates counted?
The calculator counts the number of full days from the start date to the end date. The start date itself is not counted: from January 1 to January 3 is 2 days.
Can I include the end date in the count?
If your task counts both endpoints — for example, hotel nights vs. days of stay — simply add 1 to the result.
Does it handle leap years and different month lengths?
Yes. The calculation uses real calendar dates, so February 29, 30-day and 31-day months are all handled automatically.
What is the "add or subtract days" mode for?
Enter a start date and a number of days to find a deadline or a past date — for example, "what date is 90 days from today" for a visa-free stay limit or a payment deadline.