An optical product bending prediction method of predicting bending δ of a substrate having a multilayer film formed by alternately depositing a high refractive index material and a low refractive index material by a computer performing calculation of the following Expressions to in which a is set as a first fitting parameter and T d is set as a second fitting parameter, and the first fitting parameter and the second fitting parameter have been optimized in each coating condition using a plurality of samples by steps of: designing a plurality of samples by setting a number of layers in the multilayer film, a total physical film thickness of the high refractive index layers, the total physical film thickness of the low refractive index layers, the material of the substrate, the size of the substrate; calculating a bending calculation value for each of the plurality of samples using the Expressions to with an initial first fitting parameter and an initial second fitting parameter; manufacturing each of the plurality of samples on the basis of the design; measuring a bending measurement value for each of the plurality of samples; and determining the first fitting parameter and the second fitting parameter so that the bending calculation value is fitted to the bending measurement value in each of the plurality of samples, δ = 3 l 2 b 2 1 − ν s E s dσ A 1 σ = aσ int + α s − α f E f 1 − ν f T − T d B 1 d = d H + d L C σ int = d ̃ H σ H + d ̃ L σ L D d ̃ H = d H / d E d ̃ L = d L / d F E f = d ̃ H E H + d ̃ L E L G ν f = d ̃ H ν H + d ̃ L ν L H α f = d ̃ H α H + d ̃ L α L I where σ int is intrinsic stress, E f is a Young's modulus of the multilayer film, E H is a Young's modulus of the high refractive index layer, E L is a Young's modulus of the low refractive index layer, v f is a Poisson's ratio of the multilayer film, v H is a Poisson's ratio of the high refractive index layer, v L is a Poisson's ratio of the low refractive index layer, α f is a coefficient of linear expansion of the multilayer film, α H is a coefficient of linear expansion of the high refractive index layer, α L is a coefficient of linear expansion of the low refractive index layer, α s is a coefficient of linear expansion of the substrate, T is a room temperature, d is a film thickness, b is a thickness of the substrate, l is a radius of the substrate, E s is a Young's modulus of the substrate, v s is a Poisson's ratio of the substrate, d H is a total film thickness of the high refractive index layer, d L is a total film thickness of the low refractive index layer, σ H is intrinsic stress of the high refractive index layer, and σ L is intrinsic stress of the low refractive index layer. designing a plurality of samples by setting a number of layers in the multilayer film, a total physical film thickness of the high refractive index layers, the total physical film thickness of the low refractive index layers, the material of the substrate, the size of the substrate; calculating a bending calculation value for each of the plurality of samples using the Expressions to with an initial first fitting parameter and an initial second fitting parameter; manufacturing each of the plurality of samples on the basis of the design; measuring a bending measurement value for each of the plurality of samples; and determining the first fitting parameter and the second fitting parameter so that the bending calculation value is fitted to the bending measurement value in each of the plurality of samples, δ = 3 l 2 b 2 1 − ν s E s dσ A 1 σ = aσ int + α s − α f E f 1 − ν f T − T d B 1 d = d H + d L C σ int = d ̃ H σ H + d ̃ L σ L D d ̃ H = d H / d E d ̃ L = d L / d F E f = d ̃ H E H + d ̃ L E L G ν f = d ̃ H ν H + d ̃ L ν L H α f = d ̃ H α H + d ̃ L α L I where σ int is intrinsic stress, E f is a Young's modulus of the multilayer film, E H is a Young's modulus of the high refractive index layer, E L is a Young's modulus of the low refractive index layer, v f is a Poisson's ratio of the multilayer film, v H is a Poisson's ratio of the high refractive index layer, v L is a Poisson's ratio of the low refractive index layer, α f is a coefficient of linear expansion of the multilayer film, α H is a coefficient of linear expansion of the high refractive index layer, α L is a coefficient of linear expansion of the low refractive index layer, α s is a coefficient of linear expansion of the substrate, T is a room temperature, d is a film thickness, b is a thickness of the substrate, l is a radius of the substrate, E s is a Young's modulus of the substrate, v s is a Poisson's ratio of the substrate, d H is a total film thickness of the high refractive index layer, d L is a total film thickness of the low refractive index layer, σ H is intrinsic stress of the high refractive index layer, and σ L is intrinsic stress of the low refractive index layer.