Guide
How to Calculate Your Age from a Date of Birth
Understand how calendar dates are compared to calculate age in completed years.
Key idea
Understand how calendar dates are compared to calculate age in completed years.
Formula or method
Age is the year difference adjusted if the birthday has not yet occurred.
Worked example
Start with the values in your question, substitute them into the formula, and keep the units consistent. For example, if a rate is given as 15%, use 0.15 when a formula requires a decimal.
Common mistakes
- Mixing percentage points with percentage change.
- Using different units for the same calculation.
- Rounding too early when several steps are involved.
Tip: Use the matching AvyTool calculator to check your result after working through the method.
Why the result can differ
Real-world calculations can include assumptions, rounding, fees, tax rules, calendar conventions, or other details. Treat simple calculator results as estimates when the underlying situation is more complex.