function module to predict the date for a given date

hi friends,

is there any function module to predict the date

means for example if i enter one date , what will be the date

after 4 months(say) to the given date.

my requirement is when a person is hired today (10.06.2008)

and if he is under probationary for 6 months, then on what date he comes into the permenant employee's list(predicted date after date 6 months)