The amount of the old-age basic pension is the amount obtained by multiplying 780,900 yen by the revision rate (meaning the rate set under the provisions of paragraph (1) of the following Article and revised under the provisions of that Article (excluding paragraph (1)) through Article 27-5; the same applies hereinafter) (if a fraction of less than 50 yen arises in that amount, it is to be rounded down, and if a fraction of 50 yen or more but less than 100 yen arises, it is to be rounded up to 100 yen). However, when paid to a person whose number of months of premium-paid periods is less than 480, the amount is the amount obtained by multiplying that amount by the number obtained by dividing the number of months obtained by combining the numbers of months listed in the following items (480 being the maximum) by 480.
The number of months of premium-paid periods;
保険料納付済期間の月数
A number of months corresponding to seven-eighths of the number of months of the one-quarter premium exemption period (the number of months obtained by deducting the number of months of premium-paid periods from 480 being the maximum);
保険料四分の一免除期間の月数（四百八十から保険料納付済期間の月数を控除して得た月数を限度とする。）の八分の七に相当する月数
A number of months corresponding to three-eighths of the number of months obtained by deducting, from the number of months of the one-quarter premium exemption period, the number of months of the one-quarter premium exemption period prescribed in the preceding item.
保険料四分の一免除期間の月数から前号に規定する保険料四分の一免除期間の月数を控除して得た月数の八分の三に相当する月数
A number of months corresponding to three-quarters of the number of months of half premium exemption periods (the number of months obtained by deducting, from 480, the number of months obtained by combining the number of months of premium-paid periods and the number of months of the one-quarter premium exemption period, being the maximum);
保険料半額免除期間の月数（四百八十から保険料納付済期間の月数及び保険料四分の一免除期間の月数を合算した月数を控除して得た月数を限度とする。）の四分の三に相当する月数
A number of months corresponding to one-quarter of the number of months obtained by deducting, from the number of months of half premium exemption periods, the number of months of half premium exemption periods prescribed in the preceding item;
A number of months corresponding to five-eighths of the number of months of the three-quarter premium exemption period (the number of months obtained by deducting, from 480, the number of months obtained by combining the number of months of premium-paid periods, the number of months of the one-quarter premium exemption period, and the number of months of half premium exemption periods, being the maximum);
保険料四分の三免除期間の月数（四百八十から保険料納付済期間の月数、保険料四分の一免除期間の月数及び保険料半額免除期間の月数を合算した月数を控除して得た月数を限度とする。）の八分の五に相当する月数
A number of months corresponding to one-eighth of the number of months obtained by deducting, from the number of months of the three-quarter premium exemption period, the number of months of the three-quarter premium exemption period prescribed in the preceding item;
保険料四分の三免除期間の月数から前号に規定する保険料四分の三免除期間の月数を控除して得た月数の八分の一に相当する月数
A number of months corresponding to one-half of the number of months of the full premium exemption period (excluding one relating to a premium that a person has been made not required to pay under the provisions of Article 90-3, paragraph (1)) (the number of months obtained by deducting, from 480, the number of months obtained by combining the number of months of premium-paid periods, the number of months of the one-quarter premium exemption period, the number of months of half premium exemption periods, and the number of months of the three-quarter premium exemption period, being the maximum).
保険料全額免除期間（第九十条の三第一項の規定により納付することを要しないものとされた保険料に係るものを除く。）の月数（四百八十から保険料納付済期間の月数、保険料四分の一免除期間の月数、保険料半額免除期間の月数及び保険料四分の三免除期間の月数を合算した月数を控除して得た月数を限度とする。）の二分の一に相当する月数