Calendar years are not all the same length
Most years have 365 days, while leap years have 366. This is why an exact age should use calendar boundaries rather than a fixed day count.
Years, months, and days
A calendar-based age calculation subtracts complete years first, then complete months, then remaining days. Month lengths are also different.
Elapsed days are still useful
For project schedules and countdowns, total elapsed days may be more useful than years and months. The date difference calculator provides that view.
Inclusive versus exclusive dates
An elapsed duration normally excludes one endpoint. If a schedule needs to count both the first and last day, use inclusive counting.
Try the calculator
Use the calculator below when you want to apply the formula to your own numbers.
Open Age Calculator →Methodology: QuickSolve guides explain common mathematical formulas in plain language. Where institutions, lenders, employers or accounting systems use their own rules, those official rules take priority.