I am just wondering what other developers think is the best formula for calculating a leap year.

Say, for example, you want to show a date that is 12 months later than the date the user enters. (Note that's 12 MONTHS, not 365 days later.)

So, if the date entered is 3/31/2011, result would be 2/29/2012 and if he enters 3/31/2012, the result would be 2/28/2013.

How about Date ( Month ( inputDate ) ; Day ( inputDate ) ; Year ( inputDate ) + 1 ) - 1?