Illustrative example. The dates and amounts below are provided for practice.
A February 29 birthday needs an agreed observance date in 2027. One person may want a greeting on February 28 while another prefers March 1.
Run a controlled comparison
Enter month 2, day 29, no birth year, and Calculate As Of February 27, 2027. Choose February 28 in common years and calculate. The next birthday is February 28, one elapsed day away.
Change only the rule to March 1 in common years and recalculate. The target becomes March 1, two elapsed days away. In inclusive numbering from February 27, those targets would be Day 2 and Day 3.
Save the preference, not a rewritten birthday
Keep month 2 and day 29 on the tracker record and save the preferred rule in the expandable options. Replacing the original date with February 28 would lose the leap-year birthday.
This comparison concerns celebration planning. It does not settle any official rule about age or eligibility. Ask the person which date to use, then keep that preference consistent between the countdown, the tracker, and any exported calendar instances.