Macro to calculate billing amounts based on dates

[dfuhrman08]

I have trying to work on a macro that would give me billing amounts based on a subscription start date and the annual fee.
Column J has the annual subscription start date
Column L has the Annual fee paid.

January billing - Column M is where I am needing to calculate the fee for 1/1(current year)-6/30(current year)
July Billing - Column N is where I am needing to calculate the fee for 7/1(current year)-12/31(current year)

For January billing, if current year>start date year, then January billing (Column M) needs to equal Annual fee paid. (Column L)
If current year is <= start date year, then January billing (Column M) needs to be zero.
If Current year = start date year, then if start date month >6, then January Billing = zero. Else, January Billing = (Annual Fee/12)*(7-Month(Start Date)

For July Billing, if current year>start date year, then July billing(Column N) equals Annual Fee(Column L)/2
If current year<year start date, then July billing = zero
If current year =Year(start date) then if month(Start date)<7, then July billing = (Annual Fee/2), else July billing = (Annual Fee/12)*(13-Month(start date))

I just cannot get my formula or macro correctly written to figure these two columns of finding January and July Billing.
Any help that I can get would be appreciated.