1. Select a cell and enter your date of birth.
2. Select the cell next to it and enter the TODAY function to return today's date.
3. The most difficult part in order to get the number of days until your birthday is to find your next birthday. The formula below does the trick.
Explanation: The DATE function accepts three arguments: year, month and day. We used the DATEDIF function to find the number of complete years ("y") between Date of Birth and Today. DATEDIF(A2,B2,"y") equals 37. If 37 complete years have passed since your date of birth (in other words, you have already celebrated your 37st birthday), your next birthday will be 37 + 1 = 38 years after your date of birth.
4. Next, we use the DATEDIF function to find the number of days ("d") between Today and Next Birthday.
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