A physical age calculating method and a body fat measuring system are provided. The physical age calculating method includes the following steps: A plurality of body parameters are received by an input interface. A body fat percentage is calculated according to the body parameters. A presumed muscle weight is calculated according to the body fat percentage. A presumed muscle percentage is calculated according to the presumed muscle weight. A physical age is calculated according to the presumed muscle percentage.一種身體年齡計算方法及體脂量測系統。身體年齡計算方法包括以下步驟：透過一參數單元接收數個身體參數。根據此些身體參數計算出一體脂率。根據體脂率計算一虛擬肌肉體重。根據虛擬肌肉體重計算一虛擬肌肉比。根據虛擬肌肉比計算身體年齡。
