Illustrative example. The dates and amounts below are provided for practice.
A relationship began January 1, 2024, and the celebration is intended to mark 1,000 complete days. This differs from calling the starting date Day 1.
Enter January 1, 2024, select 1000 Days, and choose After starting date. The target is September 27, 2026, Sunday.
Verify the count in reverse
In Days Together, calculate from January 1, 2024 until September 27, 2026. The elapsed result is 1,000, while Inclusive Day Number is 1,001.
Inclusive Day 1,000 would occur September 26. The one-day difference is the initial counted date, not a rounding adjustment or an alternate leap-year rule.
Use the date realistically
If the gathering is on the preceding Saturday, give the celebration plan September 26 and keep September 27 in a note as the elapsed milestone. That makes the scheduling choice visible.
Save the milestone as one time. The next calendar anniversary still follows January 1, and a future multiple of 1,000 days should be calculated from the original relationship start. Repeating September 27 annually would create a different kind of event.