Difference · add · subtract
Date Calculator
How many days between two dates, how many of them are working days, and what date falls a given period before or after another. Calendar-aware, so months and leap years come out right.
Days between
Difference Between Two Dates
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Days between
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Inclusive
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Working days
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Weeks
| Expressed as | Value |
|---|
Add or subtract
Move a Date Forwards or Backwards
Months and years are added by the calendar. One month after 31 March is 30 April, because there is no 31st.
Result
Where it gets used
What People Calculate Dates For
| Situation | Which figure | Worth knowing |
|---|---|---|
| Notice periods | Add months | Usually calendar months from the date given, not thirty-day blocks |
| Payment terms | Add days | Net 30 means thirty days from the invoice date, weekends included |
| Project deadlines | Working days | Subtract public holidays yourself; they vary too much to assume |
| Hotel and hire bookings | Days between | Nights, not days — three nights spans four calendar dates |
| Passport and visa validity | Add months | Many countries require six months remaining beyond your return date |
| Return and warranty windows | Add days | Count from delivery rather than from the order date |
| Anniversaries and milestones | Days between | Round numbers like 1,000 days are easier to spot with the total |
Answers
Date Calculator Questions
Inclusive counting, working days, calendar months and leap years.
Does the difference include both the start and end dates?
The main figure counts the days between them, so 1 January to 2 January is one day. The inclusive count, which treats both endpoints as part of the span and gives two, is shown alongside it. Contracts, hire periods and hotel bookings vary in which one they mean, so both are given rather than making you guess.
What counts as a working day?
Monday to Friday, excluding weekends. Public holidays are not deducted, because they differ by country, region and sometimes by employer, and a figure that silently used the wrong calendar would be worse than one that plainly does not try. Subtract the holidays you know about from the result.
Why does adding one month sometimes land on a different day number?
Because months are not all the same length. One month after 31 January cannot be 31 February, so the convention used here is to clamp to the last valid day of the target month, giving 28 or 29 February. This is what a person with a wall calendar does, and it is what most legal and financial conventions specify.
How is age in years, months and days worked out?
By calendar rather than by division. The years are counted first, then the whole months remaining, then the days. That is why the answer is not simply the total days divided by 365.25 — the calendar method is what people mean when they say they are thirty-four years and two months old.
Are leap years handled?
Yes, throughout. A year is a leap year if it divides by four, except centuries, unless they divide by 400 — which is why 2000 was one and 1900 was not. Both the difference and the add or subtract calculations work from the real calendar rather than an assumed year length.
Does it account for daylight saving?
These calculations work in whole calendar days, so clock changes do not affect them. A date is a date regardless of whether the day it names happened to be 23 or 25 hours long. If you need hours rather than days, the countdown timer handles clock changes properly.
What date range does it accept?
Any date the calendar supports, past or future, across century boundaries. Historical dates before the Gregorian calendar was adopted are calculated proleptically — that is, as if the modern calendar had always been in force — which is standard practice but will not match historical records from countries that switched later.