Jul 12 2022 11:51 PM - edited Jul 12 2022 11:53 PMSolution
@Priyanshu1325 Here the sum formula includes C3 which most likely is a real date. If it contains 1 Feb 2019 that represents a numerical value of 43497. Add to these the numbers below it and you'll end up with a number 45197 which Excel then automatically translates to the date 28 Sep 2023, since C3 is also a date. A bit awkward, but that's how it is. Exclude C3 from the SUM or change the header row to texts.
Edit: Excel stores dates as sequential numbers, starting at 1 for January 1, 1900.