WhenMathDate Difference Calculator
Find how far apart two dates are, shown two ways: the elapsed day count, and the calendar period (years, months, weeks, days) that a person would naturally describe.
Worked example
From January 1 to February 1, 2027, there are 31 elapsed days (January's full length), but the calendar period is exactly 1 month. From February 28 to March 1, 2028, there are only 2 elapsed days, since 2028 is a leap year and February has 29 days that year; without checking the leap-year status of 2028, it's easy to miscount this span by a day.
Two different answers, both correct
"How many days" and "how long" are different questions. Elapsed days is a precise count of [start, end); calendar period is the same span expressed the way people actually talk about durations, borrowing from the preceding unit exactly like subtraction with regrouping. Neither is more correct; they answer different questions.
Limitations
This is calendar arithmetic only; it does not determine any legal or contractual notice period.
Frequently asked questions
- Which number should I use?
- Use elapsed days for a precise count (such as billing or aging); use the calendar period for a natural description (such as "about 3 months").