What is a day calculator?
A day calculator works with calendar dates. It can tell you how many days there are from one date to another, or which date you reach if you add or subtract a number of days. People use it for countdowns, deadlines, pregnancy and project timelines, notice periods, return windows and anything else measured in days.
Doing this by hand means tracking months of different lengths and leap years, which is easy to get wrong. The calculator handles all of that for you.
How to count the days between two dates
- Count the days left in the start month.
- Add the full months in between, using each month's real length (28 to 31 days).
- Add the days in the final month up to the end date.
Standard counting does not include the end date. If you do want both the first and last day counted, which is common for event lengths, add 1 or use the include end date option.
Adding and subtracting days
To add days to a date, move forward that many days, rolling over into the next month or year when needed. Subtracting works the same way backwards. A good shortcut is to split into weeks first: 90 days is 12 weeks and 6 days, so the date lands six days past a date that is exactly 12 weeks later, and the weekday shifts by six.
Remember that every 7 days returns you to the same weekday. If you add a number that is a multiple of 7, the weekday of the answer is unchanged.
Business days
Business days are the weekdays, Monday through Friday. This tool counts them from the start date up to, but not including, the end date (or including it when you tick that option). It does not remove public holidays, because holidays differ by country, state and employer.
For delivery or legal deadlines, subtract the holidays that apply to you from the business day count shown here.
Months and days
The months and days breakdown counts whole calendar months from the start date and then the leftover days. Because months are not equal in length, it is a calendar measure and not a fixed number of days. Jan 31 to Feb 28, for example, is shown as 0 months and 28 days since a full month has not yet passed.
| Span | Days |
|---|---|
| 1 week | 7 |
| 30 days | About 1 month |
| 1 common year | 365 |
| 1 leap year | 366 |
Things that change the answer
- Include or skip the end date. This changes the total by one day.
- Leap years. February has 29 days in leap years, such as 2028.
- Time zones and times of day. This calculator works with whole dates only, so it is not affected by them.
- Holidays. Not removed from business day counts.