To provide a fertilization optimum time calculating scale for mammals capable of easily recognizing the time and a period relating to the sexual cycle of the female of the mammal and the fertility of the sperms of the male and the fertility intensity of ovum and the sperms and appropriately deciding the fertilization timing with the high possibility of conception.

The fertilization optimum time calculating scale for the mammals is a slide type calculation scale and is constituted of: a time rule for which the time is a scale as a fixed rule; a female rule with a scale including the indication of a prescribed timing in the estrus of the female of a prescribed mammal and an ovum fertility intensity display part expressing the fertility intensity of the ovum in the fertilizable period of the ovum by a surface shape as a slide rule; and a male rule functioning as a cursor, for which a scale including the indication of the fertilization timing of the sperm and a sperm fertility intensity display part expressing the fertility intensity of the sperm in the fertilizable period of the sperm by a surface shape on a transparent plate. As the female rule and the male rule are relatively slid, the optical state of the overlapping surface of the surface of the ovum fertility intensity display part and the surface of the sperm fertility intensity display part is different from the surface of the respective fertility display parts.