Illustrative example. The dates and amounts below are provided for practice.
A scrapbook is being prepared ahead of a thirtieth birthday. The future date belongs in the reference field, even though the person's current age is lower.
Use Date of Birth November 20, 1997 and Calculate Age As Of November 20, 2027. Calculate. The result is 30 years, zero months, zero days, with 10,957 total elapsed days.
Check the message on both sides
Change the reference to November 19, 2027. Only 29 full years are complete. Return to November 20 before copying the final caption.
The 10,957-day figure includes leap days within the interval. Multiplying 30 by 365 would omit seven days. If you count birth as Day 1, the anniversary is inclusive Day 10,958, but the elapsed output remains 10,957.
Keep the future date visible
A printed caption can use the age at the intended celebration. A statement about someone's age today needs today's date instead. Keep the reference date beside any saved result so the context survives.
If the gathering moves to a weekend, the birthday age is still anchored to November 20. Choose the actual photograph date if you later add a picture taken at the rescheduled party.