How do I estimate the full monthly cost, not just principal and interest?

Add property taxes, homeowner's insurance, HOA dues if any, and PMI if your down payment is under the threshold your lender uses, on top of principal and interest, to reach the true monthly cost. Property taxes in Georgia are billed on an assessed value equal to 40 percent of fair market value, then taxed at a millage rate your county and city set each year, so that piece varies by where you buy. A lender can run the exact full payment for a specific North Metro Atlanta property.