Answer:
As long as your penalty is always at least equal to 7 days' interest on the amount withdrawn if the withdrawal is less than 7 days from the deposit date or last withdrawal date, how you calculate the penalty is a matter of contract, which might be subject to some state law restrictions.
I haven't worked the math, but it appears your suggested penalties would pass the test.
First published on BankersOnline.com 06/9/03