Fixed Annual/Semi-Annual Bills

Dear all,

We have 2 fixed Billing cycles
1-Annual on 07.February of each year (covers from 07.Feb Till 06.Jan of next year)
2- Semi-Annual on 07.February (2 times a year From 07.Feb. Till next 06.Aug and then 07.August Till 06.Feb)
am trying to find find formulas to get the FIRST Bill cycle date and LAST Bill Cycle date based upon start date of service and last date of service

A B C D E F
1 Service Start Date 1st Billed on End Date Last Billed on Bill Cycle Type
2 DIA 05-Feb-2011 07-Feb-2011 25-Dec-2012 07-Feb-2012 Annual
3 VPN 14-Jul-2009 07-Aug-2009 25-Apr-2014 07-Feb-2014 Semi-Annual

Can we have these formulas in C and E, as am building other calculations based on these formulas?

Appreciate your help,, It's OK if there's a way with VB and formulas did not workout