How it works
Pick two dates to see how many days separate them. By default the count excludes the end date, so Monday to Tuesday is one day. Turn on "Include end date" when you need to count both the first and last day, such as for the length of an event or a leave period.
The result is also broken down into weeks and days and into calendar years, months and days. Leap years are handled automatically because every real calendar day is counted.
Formula
Days = (end date − start date) ÷ 86,400,000 ms, plus 1 if the end date is included.
Questions people ask
Should I include the end date?
Exclude it for elapsed time (how long from one date to the other). Include it when both days count, such as a hotel booking of nights versus days, or a vacation from the 1st through the 5th, which is 5 days.
Does daylight saving time affect the result?
No. Dates are compared as whole calendar days, so a 23- or 25-hour day at a clock change still counts as one day.
How many days are in a year?
365 in a common year and 366 in a leap year. Leap years are divisible by 4, except century years, which must be divisible by 400 (2000 was a leap year, 1900 was not).