Step 1: Monthly Depreciation Charge
(CC – RV) / M

Step 2: Monthly Finance Charge
(CC + RV) * MF

Step 3: Total Monthly Charge (plus tax)
(Monthly Depreciation Charge + Monthly Finance Charge) * LST

MF: The Money Factor. (You can find out what your interest rate is by multiplying the money factor by 2400)
RV: Residual Value. What the car is worth at lease-end.
CC: The Capitalized Cost AKA Sale Price.    
LST: Local Sales Tax.
M: Term of the lease (24,36,48,etc)