Excel VBA Functions- Perform Calculation if Value is found to be within Specified Range

Hi Experts,

I have a workbook where I need to manage vacation accrual throughout a calendar year.  

On the 1st of each month I need the accrued vacation hours amount (stored in column "E") to be added to the "Previous PTO BAL AVAIL" column (" I ") and then place the new amount in the "PTO Bal" column (" J ").

For Ex:

I need the code to work as follows:  

1.

Find TodaysDate in the "RenewalMonth" range column "AA"

2.

Add "hours accrued" (col "E") to the "Previous PTO Bal Avail"

3.

Store the new balance to be in "PTO Bal" column "J"  

**The tricky part, when a new month start I would need the amount stored in the "PTO Bal" column to now be stored in the "Previous PTO Bal Avail" column and then run through steps 1 - 3 again**
I attempted to record a Macro to see if I could figure out how to get this to work but I'm more confused now than before..

    Range("J6").Select
    ActiveCell.FormulaR1C1 = _
        "=IF(OR(TodaysDate=R[-2]C[17],R[-1]C[17],RC[17],R[1]C[17],R[2]C[17],R[3]C[17],R[4]C[17],R[5]C[17],R[6]C[17],R[7]C[17],R[8]C[17],R[9]C[17],R[10]C[17],R[11]C[17],R[12]C[17],R[13]C[17],R[14]C[17],R[15]C[17],R[16]C[17],R[17]C[17],R[18]C[17],R[19]C[17],R[20]C[17],R[21]C[17]),SUM(R[-1]C[-5],R[-1]C[-1]),R[-1]C[-1])"
    Range("J6").Select

Thank you for your time in Advance!  :)
SampleVacationAccrual.xlsm