The maximum ratio of the amount of rent increase to be applied in renewals of lease agreements is clearly determined in the law of Obligations (M 344). Accordingly, the rent increase rate can be as much as the ”Consumer Price Index” ratio of the domestic Producer Price Index. But the explanation of four different values of Consumer Price Index by Turkish Statistical Institute: ”exchange rate according to twelve-month averages” , ”annual exchange rate” , ”exchange rate according to December” and ”monthly exchange rate” creates confusion. According to the established decisions of the Supreme Court, the rate to be applied as the rate of rent increase is the ”rate of change relative to the twelve-month averages of Consumer Price Index. If the rent increase rate written in the contract is lower than Consumer Price Index, the amount of increase written in the contract will apply. Conversely, if a rent increase greater than this rate is determined in the lease agreement, the rent increase rate determined will not be applied because it will be contrary to the mandatory provisions of the debt law, the Consumer Price Index rate will be applied.