What the span equals in each unit
The days between two dates is the base figure; everything else is a conversion of it. Weeks and years are exact divisions, while months vary because calendar months are not all the same length.
Calendar days vs business days
Calendar days count every day. Business days count only Monday to Friday, so the same span reaches much further ahead on the calendar. Public holidays are not removed unless you account for them yourself.
The details that change the count
- Whether the end day counts. Excluding it measures the gap between the dates; including it measures the number of days occupied. The two differ by exactly one day.
- Months are not fixed. Counting whole months by the calendar is exact; using an average of 30.44 days per month is an estimate that drifts over long spans.
- Leap days add up. Each February 29 inside the range adds a day, which matters for age, tenure and interest calculations.
Common questions
How do you count the number of days between two dates?
Subtract the earlier date from the later one. Whether the result includes the end day depends on your intent: a hotel stay counts nights (end day excluded), while a trip length in days often counts both ends. The include-end-date option adds one day to the total.
How many weeks and months is a given number of days?
Divide the days by 7 for weeks and by about 30.44 for the average month. Whole calendar months are more exact when counted by the calendar, since real months run 28 to 31 days.
Does the calculator handle leap years?
Yes. Any February 29 inside the range is counted, so a span crossing a leap day is one day longer than the same span in an ordinary year.
