THE NUMBERS, EXPLAINED
How to use this calculator.
Uses completed calendar years. For a February 29 birth, the anniversary is March 1 in non-leap years. No birth date is sent to a server.
Start with your inputs
Enter date of birth, reference date. Keep amounts in the units shown on each field. The example is a starting point, not a recommended value.
| Input | Example value |
|---|---|
| Date of birth | 2000-01-01 |
| Reference date | 2026-01-01 |
A worked example
With the example inputs above, completed years is 26. Change the inputs to explore your own scenario.
| Result | Example answer |
|---|---|
| Completed years | 26 |
How this is calculated
Completed years
completedYears(a,b)
Symbols and units
- a
- Date of birth
- b
- Reference date
Use the units shown. A list keeps the order in which you enter its values. The symbol ^ means “raised to the power of”.
Calculation steps and notation
Subtract birth year from reference year, then subtract one if the reference month and day precede the birthday. A 29 February birthday advances on 1 March in a non-leap year under this convention.
Assumptions and limits
Uses completed calendar years. For a February 29 birth, the anniversary is March 1 in non-leap years. No birth date is sent to a server.
Calculations use the values you enter. Blank or invalid inputs show an error instead of silently substituting zero. Results are displayed to useful precision; calculations retain the underlying numeric precision.
Questions about this tool
What does the result tell me?
Completed years. The result applies to the method and inputs described above. Check the units and assumptions before using it in a decision.
Why might another calculator differ?
Differences in units, rounding, timing or model definitions can produce different answers. Compare the input definitions and the method, rather than only the final number. For this tool: Uses completed calendar years. For a February 29 birth, the anniversary is March 1 in non-leap years. No birth date is sent to a server.
Are my inputs stored or sent to AI?
Calculations on this page happen in your browser. The separate AI question finder sends its submitted conversation to OpenAI; these calculator fields are not sent. Favourites and recent tool names are stored locally. A shared link contains the inputs you choose to include.
Review status
Software example and browser checks are recorded in our quality report. No external expert review is claimed. Created with coding assistance; calculations run as ordinary browser code.
Read the quality report →