Decision tools built for clarity
Age Calculator
Calculate completed age and total elapsed days between two dates.
Enter the required values, select the applicable options, and calculate.
Methodology
Formula or transformation
Computes completed Gregorian calendar components and the exact elapsed whole-day interval.
Variables
- Birth date
- Age calculation date
- Completed years
- Completed months
- Completed days
- Total elapsed days
Units
- Year
- Month
- Day
Rounding policy
Calendar components and total days are whole integers; no fractional date is displayed.
Calendar components are calculated as completed Gregorian years, months, and days; total days is the signed date interval.
Calculate completed age and total elapsed days between two dates.
Reviewed sources
- PHP Documentation — DateTimeInterface::diff calendar difference Reviewed on 2026-09-07
Formula review history
-
Initial formula and source review.
Reviewed 2026-09-07 for formula version gregorian-completed-age-v1
Assumptions
- Inputs are interpreted using the displayed units and options.
- The calculation follows the methodology and factors listed in the sources.
Limitations
- Display rounding can hide additional decimal places.
- The calculation cannot add accuracy that is absent from the submitted inputs.
Worked example
A birth date of 7 September 1990 and an as-of date of 7 September 2026 gives 36 years and 13,149 total days.
Frequently asked questions
Are the calculations deterministic?
Yes. The same valid inputs and options produce the same canonical result.
Can I use decimal values?
Use decimal values where the displayed input accepts them.