Find next payday and last payday

[Alpacino]

Hi all,

I have a problem. I want to find out when my next payday will be and last payday by using today date and type of pay period. e.g. weekly, fortnightly, monthly or 4 weekly. and just a day. e.g 26th or 26

Say today = 14/09/11

I get paid 4 weekly.

I got paid last time on the 26

Any ideas I tried this formula to work the next payday but I need an input of the date before for it to work.

C5 = Today()

=IF($C$5="Monthly",DATE(YEAR(I6),MONTH(I6)+1,DAY(I6)),IF($C$5="4 Weekly",I6+28,IF($C$5="Weekly",I6+7,I6+14)))