It's because the underlying value is not 0.99, it's in fact

0.989999999999998



You could remedy this in your case by using this

=IF(ROUND(16.99-16,2)=0.99,10,0)


that's the way computer works, see these links for an explanation

http://www.mcgimpsey.com/excel/pennyoff.html

http://www.cpearson.com/excel/rounding.htm


--


Regards,


Peo Sjoblom





"tlaurie777" wrote in message
...
=IF((16.99-16)=0.99,10,0)

In this function, any number from (1.99-1) through (15.99-15) works and
any
number above (16.99-16) fails.