Today, with a fluctuating course of the economy, it is inevitable that the interest method used by people for investment will also fluctuate. There may be serious inconsistency between the current interest rate and the interest rate at the time of the investment. Therefore, in order to eliminate these inconsistent situation, fuzzy set theory is used and the case where the interest rate parameter is fuzzy variable is examined. In this way, it is provided that the uncertain interest rate is close to the real-life interest rate.