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A birth date of 29 February remains the original birth date even when a later year has no 29 February. The calculator therefore needs an explicit anniversary rule. QiLoom uses 1 March in non-leap years and 29 February in leap years. This is the tool's convention, not a determination of legal eligibility in Singapore or elsewhere.
Separate the record from the annual anniversary
The historical birth date does not change. The anniversary is the date used in a particular year to decide whether another complete year has elapsed under the chosen rule. A family may celebrate on 28 February or another convenient day while retaining the original record. Do not change the birth date just to make a reminder or form easier to enter.
Work through a concrete example
For someone born on 29 February 2000, the calculator gives 24 completed years on 28 February 2025 and 25 on 1 March 2025. In 2028 it gives 27 on 28 February and 28 on 29 February. Subtracting birth year from reference year is only the first step: the reference date must also have reached that year's anniversary.
A leap-day birthday does not mean ageing once every four years
Completed age is not the count of how often 29 February has appeared on a calendar. Time continues through non-leap years, and the stated anniversary rule handles their missing date. Nor should a long-term reminder assume every fourth year is automatically a leap year: Gregorian century rules make 2000 a leap year but 2100 a non-leap year.
Keep the countdown consistent with the age
A countdown should target the same anniversary convention used for age. Otherwise one part of a page can point to 28 February while another increases age on 1 March. Check the displayed next-anniversary date, not only the number of days. A countdown of zero refers to the selected calendar date, not to the precise hour of birth.
Record the reference date when sharing a result
The same birth date can give different ages immediately before and after the anniversary. Write 'as of' followed by the full reference date so another person can reproduce the result. A reference date before birth is not a valid age calculation. If only a birth year is known, the missing month and day may prevent one exact completed-age answer.
Use formal requirements for formal decisions
A school, competition or other organisation may specify its own reference date and interpretation. Read those requirements rather than treating this general calculator as the final authority. For personal planning, use the age and birthday countdown tool, then compare the relevant dates with the day-difference calculator. Keep the reference date and anniversary rule consistent across both checks.