PURPOSE: To obtain the portable gauge with which a menstrual period can easily be calculated by indicating the details of menstrual periods, varying with individuals, on a dial gauge.

CONSTITUTION: This portable gauge for menstrual period calculation consists of three circular ring scales A, B, and C which are made of transparent hard plastic and different in diameter. The scale A is a circular date ring having the largest diameter, engraved with 60 dates, and fitted as a bottom ring. The scale B is a circular ring on which safe periods are displayed and has an intermediate diameter, and is bound between the scales. The scale C is a circular ring which has a projection part specifying individual differences in menstrual period from a 25-day type to a 35-day type and bound as the top ring. A menstrual type of the scale C is set to the end period of menstruation of the scale B and then the ending day of a last previous menstrual period is set to the date of the scale A, so that the safe period of the scale B is indicated as a date of a next month of the scale A.