Date Calculator

How to use the Date Calculator

1. Choose a start date and an end date. Both start on today’s date from your device, with the end 30 days ahead.
2. Choose how to count: Exclude start date (the usual way) or Include both dates.
3. Press Calculate. The result shows calendar days, business days, weeks, months and years together.
4. Use Calculate difference as to make calendar days or business days the large headline figure. The other figures stay visible either way.

The quick ranges, from Today → Today to Today → +1 year, set both dates in one tap: handy for questions like “how many business days are in the next 30 days?”. If the end date is before the start date, the calculator still answers, says that the end date is earlier, and offers to swap the dates.

How many days are between two dates?

The number of days between two dates is how many times the calendar turns over to get from one to the other. From October 8, 2026 to December 25, 2026 there are 78 days: 23 left in October, 30 in November and 25 in December. That is the default, start-date-excluded count, the same answer you get by asking “how many days from now until then?”.

The calculator works on dates alone, without clock times, so a daylight saving change in between can’t make the answer a day short or long. Month lengths and leap years come from the standard Gregorian calendar.

How are business days calculated?

Business days and working days commonly refer to Monday through Friday, excluding weekends. The calculator counts every Monday, Tuesday, Wednesday, Thursday and Friday in the range and skips every Saturday and Sunday. With the start date excluded, Monday → Tuesday is 1 business day, Friday → the next Monday is also 1, and a full Monday-to-Monday week is 5.

Public holidays are not taken out. Which days are holidays depends on the country, and often the region or employer, so subtract any that fall on weekdays in your range yourself. Contracts and shipping estimates sometimes define business days differently, so check the definition that applies to you.

Calendar days vs business days

Calendar days count every day, weekends included. Business days count only weekdays. Over a long span, business days come to about five-sevenths of the calendar days: October 8, 2026 to December 25, 2026 is 78 calendar days but 56 business days, because 22 of the days are Saturdays and Sundays. Deadlines such as “within 30 days” usually mean calendar days, while “5 business days” or “10 working days” skip weekends. The calculator shows both, so you can read off whichever you need.

How weeks, months and years are calculated

Weeks are the calendar days divided by 7, shown as whole weeks and leftover days: 78 days is 11 weeks, 1 day. A decimal (about 11.14 weeks) is shown alongside for reference.

Months can’t be found by dividing, because calendar months do not all have the same number of days: they run from 28 to 31. So the calculator counts completed calendar months from the start date, then the days left over. October 8, 2026 to December 25, 2026 is 2 months (to December 8) and 17 days. When the start date is late in the month and the target month is shorter, the month is complete on that month’s last day: January 31 to February 28 is 1 month.

Years are counted the same way, as completed calendar years, then months, then days. A calendar year is not always equivalent to exactly 365 days: a leap year, such as 2028, has 366, because February has a 29th day. Years divisible by 4 are leap years, except century years not divisible by 400, so 2000 was a leap year but 2100 won’t be. Counting by the calendar means October 8 to October 8 of the next year is always exactly 1 year, whether it spans 365 or 366 days. A year that starts on February 29 ends on February 28 the following year.

Inclusive vs exclusive date counting

By default the start date is not counted and the end date is, so January 1 to January 2 is 1 day. This is how most people mean “days between” or “days until”, and it is how elapsed time works.

Choose Include both dates when every date in the range counts, as in “from June 1 to June 5 inclusive” or the number of days of a trip, event or leave period. January 1 to January 2 is then 2 days, and January 1 to December 31 is a whole year of 365 or 366 days. The choice applies to every figure, business days included, so a Monday-to-Friday week is 5 business days with both dates counted and 4 without.

Examples

February 1 to March 1 is 28 days in 2027 but 29 in 2028, a leap year, yet both are exactly 1 month: that is why months and years are counted on the calendar rather than converted from days.