Excel 2007 : Calculate # months at different rates if a date falls between two other dates

Can someone help with a formula for this: I am trying to calculate total number of months.

IF DATE A > DATE B < DATE C,
TRUE = DATE C - DATE A,
FALSE = IF DATE D = "No Charge",0,SUM COLUMNS 12,13 AND 14

where Date A is the Cancellation Date
where Date B is the Effective Start Date of the budget
where Date C is the Effective End Date of the budget
where Date D is an override that says "No Charge" and
Column 12 is # months at rate 1, Column 13 is # months at rate 2 and Column 14 is # months at rate 3.

Hope this helps.

Thanks a lot.