Why a date interval crossing February sometimes gains a day
Month lengths vary, and leap years add February 29. Multiplying a number of months by thirty is not an exact calendar calculation.
Date difference →Compare the same month and day in two years
From 2024-02-28 to 2024-03-01, the interval is two days because February 29 lies between the endpoints. From 2025-02-28 to 2025-03-01, it is one day. The calculator follows the actual Gregorian dates rather than treating every February as a 28-day month. Neither calculation needs an extra inclusive-counting adjustment unless that is the question being asked.
Remember the century exception
The year 2000 is divisible by 400 and is a leap year. The year 2100 is divisible by four but not by 400, so it is not a leap year. A long-range calculation cannot rely on the shortcut of adding one day every four years without that exception.
Match the input and interpretation
Enter a full year to avoid ambiguity from two-digit dates. This tool handles calendar dates; it does not research historical local calendar adoption or calculate actual elapsed hours across time zones. Use the age tool for completed years and the date-addition tool for a specified number of days after a start. Keeping the question explicit prevents a valid day count from being misused as a month or age result.
Try the calculators
- Date difference
Count calendar days between two dates.
- Add days to date
Find the date before or after a number of days.
- Age calculator
Find completed years and days between dates.