DIY Cost Tools
Age Calculator
TIME & DATE CALCULATOR
Age Calculator
Calculate calendar age in years, months, and days plus total elapsed days between two dates.
How it works
Enter the earlier and later dates. The calendar result borrows days from the prior month when needed, while elapsed days uses exact UTC calendar boundaries.
Formula
Calendar age subtracts year, month, and day components with calendar borrowing. Total days = difference between the two midnight UTC date values ÷ 86,400,000 milliseconds.
Worked example
From January 1, 1990 through September 29, 2026 is 36 years, 8 months, and 28 days.
Important limits
- Completed months and weeks are whole completed units, not fractional estimates.
- Calendar month lengths and leap years are included.
- Legal age rules can depend on jurisdiction and exact event timing; verify official requirements separately.
Frequently asked questions
Why do total days and calendar age look different?
Calendar age uses variable-length months and years. Total elapsed days counts every date boundary directly.
Does the result include the starting day?
It reports elapsed time between the dates, so the start date is the zero point rather than a full counted day.
Sources and review notes
The calculator uses the proleptic Gregorian calendar implemented by modern web browsers. Last reviewed September 29, 2026.