Illustrative example. The dates and amounts below are provided for practice.
A 100-day interval starting in early 2024 crosses a leap day. Replacing February with a fixed 28-day month would shift the final date.
Use Starting Date January 1, 2024, choose 100 Days, and select After starting date. The target is April 10, 2024. Repeat with January 1, 2025 and the target is April 11, 2025.
Explain the difference
Both runs add exactly 100 elapsed days. The 2024 interval contains February 29, so the same count reaches a date one day earlier in April.
An inclusive Day 100 target would use 99 elapsed days, giving April 9, 2024 or April 10, 2025. The inclusive adjustment and leap-year effect are independent.
Use a date rather than a memorized month and day
If you plan a fixed-day challenge every year, calculate each target from that year's starting date. Copying April 10 into every year would preserve a calendar date rather than a 100-day duration.
This is also why a one-time milestone and a yearly anniversary should be saved separately. Their future dates follow different rules.