It depends. Under OCGA sec. 7-4-12 judgments in Georgia shall bear interest upon the principal amount recovered at the rate of 12 percent per year unless the judgment is rendered on a written contract or obligation providing for interest at a specified rate, in which case the judgment shall bear interest at the rate specified in such contract or obligation. So, you may charge 12 percent per year unless you obtained the judgment on a written contract or obligation which provided for a specific interest rate. In that case, you can charge the interest rate specified in the written contract or obligation.
You can charge the interest rate that is stated in the written contract or obligation to pay If your judgment is based on a written contract or obligation. O.C.G.A. 7-4-12 (b).
If there isn't an amount specified for postjudgment interest, "All judgments in this state shall bear annual interest upon the principal amount recovered at a rate equal to the prime rate as published by the Board of Governors of the Federal Reserve System, as published in statistical release H. 15 or any publication that may supersede it, on the day the judgment is entered plus 3 percent" O.C.G.A. 7-4-12 (a). You can find the prime rate on the date of your judgment by going to: http://www.federalreserve.gov/Releases/H15/. Once you find the prime rate, add 3 percent and calculate the interest from the date of the judgment until the present date. It can be difficult to calculate, but you should be able to find an interest calculator online to assist you.
You may want to contact a debt collection attorney to assist you in collecting your judgment. A judgment is nothing but a piece of paper unless you can collect the money owed to you.