Guides: Calculating and Understanding Age Differences
Step-by-step guides on working out age differences by hand, choosing the right inputs, and expressing the result in days, months or years — plus reference tables of worked examples.
How-to guides
- How to calculate age difference
The formula and the hand method, with borrowing for months and days and a worked example.
- Age difference by birthday and age
What changes when you input two birthdays, two ages, or one of each — and what precision to expect.
- Age difference between two dates
How an age gap between birth dates differs from a plain date-to-date count.
- Exact age difference
Days, months, years-and-months, leap years and the February 29 convention.
- Age gap examples
Pre-computed gaps for common birth year pairs, plus rule-of-seven ranges for adult ages.
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