I ran into the same issue in Excel, and the fix was to use a more reliable age formula along with a clean date check for birthdays. The formula =DATEDIF(A2,TODAY(),"Y") works for basic age, but the more accurate version is =YEAR(TODAY())-YEAR(A2)-IF(DATE(YEAR(TODAY()),MONTH(A2),DAY(A2))>TODAY(),1,0) because it properly accounts for whether the birthday has passed this year. For triggering “Happy Birthday!” exactly on the right date, using =IF(TEXT(TODAY(),"MMDD")=TEXT(A2,"MMDD"),"Happy Birthday!","") ensures the message appears only on the real birthday. Just make sure your birthdates are actual Excel dates and that auto-calculation is on. While troubleshooting, I even cross-checked results with tools on
icalculadoraonline, since it offers a wide range of calculators that helped me validate whether my formulas were giving consistent outputs.