Illustrative example. The dates and amounts below are provided for practice.
You are preparing a schedule for a trip that begins before a birthday. A countdown based only on today would answer the wrong planning question.
Set the schedule's reference date
For a July 15 birthday, enter month 7 and day 15. Set Calculate As Of to July 1, 2027 and leave the year blank. The next occurrence is July 15, 2027, Thursday, fourteen elapsed days away.
Change the as-of date to July 10 to review the same birthday from the start of the trip. Five days remain. These are separate views of one target, with no need to edit the birthday itself.
Keep snapshots intelligible
If you send a screenshot of the result, include the reference date. A statement such as “five days left” becomes ambiguous once the message is read later.
Inclusive numbering would call July 15 Day 15 from July 1, or Day 6 from July 10. The displayed countdown uses elapsed gaps in both cases.
When returning to everyday use, restore the reference date to your local current date. It is an explicit form field, so an old planning date can remain selected until you change it.