Sorry Catalin, but A1-A2 is not a negative number. I have no idea why you think it would be.. A future date minus today will never return a negative number.

It's more serious than formatting. It's the wrong data type. Excel guesses at the data type... Text, Number/Date, or Boolean, based on the data entered. If entered incorrectly, the guess will be wrong. He can seperate it out this time using a formula simple enough, but without understanding the basics of the 1900 date system, dates will always be confusing and time-consuming.