This case, stemming from a granted application to appeal, raises two issues. The first concerns whether a trial court may modify child support retroactively. The second issue concerns the validity of a provision requiring that an ex-husband's child-support obligation be modified annually based on his annual gross income, providing that the change never be downward. 1 We affirm in part and reverse in part. The appellant ex-husband, Daniel Jarrett, and the appellee ex-wife, Linda Jarrett, were divorced in October 1979. The divorce decree provided that Daniel pay Linda $25 per child per week as child support. On November 3, 1987, Linda filed a "motion for contempt," alleging, in relevant part, that Daniel was in arrears on the child-support payments. Linda also filed a "complaint to modify" Daniel's child-support obligation. After a hearing, the court issued an order on December 16, 1988. The court did not hold either party in contempt, but it did increase the amount of Daniel's child-support obligation. The court made the modification retroactive to January 1, 1988, and provided that the amount of child support be reviewed annually and automatically adjusted based on Daniel's annual gross income, provided that this adjustment never be downward. Daniel then filed an application to appeal, which we granted. 1. Daniel first contends that the trial court improperly made the child-support modification retroactive. We agree. [A] permanent child support judgment is res judicata and enforceable until modified, vacated or set aside. Allen v. Withrow, 215 Ga. 388, 390 ( 110 SE2d 663) (1977). . . .Until a final decree amending the child support is properly entered in the modification proceeding the permanent judgment stands. Vickers v. Vickers, 220 Ga. 258 (138 SE2d 308) (1964). A child support judgment cannot be modified retroactively. Butterworth v. Butterworth, 228 Ga. 277, 279 (3) ( 185 SE2d 59) (1971). In view of the foregoing principles, the trial court in the instant case made an improper retroactive modification of Daniel's child-support obligation by ordering that the modification take effect on January 1, 1988. 2. In his second enumeration of error Daniel contends that the trial court erred in providing that the future modification of Daniel's child-support obligation could never decrease. Daniel contends that this provision improperly prohibits him from exercising his right under OCGA 19-6-19 (a) to seek a downward modification of child support based on a change in his financial status. We find no error. In Hayes v. Hayes, 248 Ga. 526, 528 (3) ( 283 SE2d 875) (1981), the trial court set alimony at $700 per month plus 25% of any gross increase the former husband received in his pension and set child support at $300 per month plus 15% of any gross increase the former husband received in his pension. The future-modification provision of the award in Hayes did not permit a decrease in the husband's obligation. However, we found no error, noting, in relevant part, that such an adjustment provision does not preclude either party from seeking modification under OCGA 19-6-19 (a). See also Wood v. Wood, 257 Ga. 598, 599 (1) ( 361 SE2d 819) (1987); Cabaniss v. Cabaniss, 251 Ga. 177, 178 (1) ( 304 SE2d 65) (1983); Golden v. Golden, 230 Ga. 867 (2) (199 SE2d 796) (1973). Based on the foregoing, we conclude that the future-modification provision of the trial court's order is proper. Leroy W. Robinson, Jr., for appellee. | 
