A calculating method is a method for calculating numerical values relating to optical properties of an eyeglass lens, the eyeglass lens comprising a close-range portion, a far-range portion for viewing distances farther than distances viewed through the close-range portion, and a mid-range portion provided between the close-range portion and the far-range portion. The calculating method comprises acquiring prescription data of a wearer, acquiring a first distance that is a distance that the wearer views through the close-range portion and a second distance that is a distance viewed through the mid-range portion, and calculating an addition power or rate of addition power at the mid-range portion that is suitable for the wearer to view the second distance, on the basis of the prescription data, the first distance, and the second distance.
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