30. What is the allocation calculation for political parties to receive public funding?

Source: 
政党助成法, 1994 (2022改正)
Political Party Subsidy Act, 1994 (as amended by Act No. 68 of 2022)

第七条　毎年分として各政党に対して交付すべき政党交付金の算定の基礎となる政党交付金の総額は、基準日における人口に二百五十円を乗じて得た額を基準として予算で定める。
２　毎年分の議員数割及び得票数割の総額は、前項の総額のそれぞれ二分の一に相当する額とする。
第八条　毎年分として各政党に対して交付すべき政党交付金の額は、次項に定める議員数割の額と第三項に定める得票数割の額とを合計した額とする。
２　各政党に対して交付すべき議員数割の額は、議員数割の総額に当該政党に所属する衆議院議員及び参議院議員の数を各政党に所属する衆議院議員及び参議院議員の数を合算した数で除して得た数を乗じて得た額とする。
３　各政党に対して交付すべき得票数割の額は、得票数割の総額の四分の一に相当する額に次に掲げる数をそれぞれ乗じて得た額を合計した額とする。
一　前回の総選挙の小選挙区選出議員の選挙における当該政党の得票総数を当該選挙における各政党の得票総数を合算した数で除して得た数
二　前回の総選挙の比例代表選出議員の選挙における当該政党の得票総数を当該選挙における各政党の得票総数を合算した数で除して得た数
三　次に掲げる数を合算した数の二分の一に相当する数
イ　前回の通常選挙の比例代表選出議員の選挙における当該政党の得票総数を当該選挙における各政党の得票総数を合算した数で除して得た数
ロ　前々回の通常選挙の比例代表選出議員の選挙における当該政党の得票総数を当該選挙における各政党の得票総数を合算した数で除して得た数
四　次に掲げる数を合算した数の二分の一に相当する数
イ　前回の通常選挙の選挙区選出議員の選挙における当該政党の得票総数を当該選挙における各政党の得票総数を合算した数で除して得た数
ロ　前々回の通常選挙の選挙区選出議員の選挙における当該政党の得票総数を当該選挙における各政党の得票総数を合算した数で除して得た数

Article 7. The total amount of political party subsidies to be delivered to each political party as the annual portion, which serves as the basis for calculating such subsidies, shall be determined in the budget based on the amount obtained by multiplying the population on the reference date by 250 yen.
2. The total amounts allocated annually based on the number of members and the number of votes shall each be equivalent to one-half of the total amount specified in the preceding paragraph.
Article 8. The amount of political party subsidies to be disbursed annually to each political party shall be the sum of the amount determined under the member-based allocation specified in the following paragraph and the amount determined under the vote-based allocation specified in paragraph 3.
2. The amount to be paid to each political party based on the number of members shall be calculated by multiplying the total amount allocated based on the number of members by the quotient obtained by dividing the total number of members belonging to the House of Representatives and the House of Councillors of the party by the combined number of members belonging to the House of Representatives and the House of Councillors of all parties.
3. The amount of the vote share subsidy to be paid to each political party shall be the sum of the amounts obtained by multiplying one-fourth of the total vote share subsidy amount by each of the following figures:
(i) The number obtained by dividing the total votes received by the party in the single-seat constituency elections of the previous general election by the total votes received by all parties in that election
(ii) The number obtained by dividing the total votes received by the party in the proportional representation elections of the previous general election by the total votes received by all parties in that election
(iii) One-half of the sum of the following numbers:
(a) The number obtained by dividing the total votes received by the party in the proportional representation election for the previous regular election by the sum of the total votes received by all parties in that election
(b) The number obtained by dividing the total votes received by the party in the proportional representation election for the members of the previous-previous regular election by the total votes received by all parties in that election
4. The number equivalent to one-half of the sum of the following numbers
(a) The number obtained by dividing the total votes received by the party in the last regular election for district-elected members by the sum of the total votes received by all parties in that election
(b) The number obtained by dividing the total votes received by the party in the election for district-elected members in the election before last by the sum of the total votes received by all parties in that election

proportional to votes received and proportional to seats received both matter.  The total sum of subsidies is 250 yen times the population. A half of this amount is distributed to parties in proportion to their seats. Another half is distributed to parties in proportion to (1) the votes they got in the most recent House of Representatives election, (2) the votes they got in the most recent House of Councillors election, and (3) the votes they got in the House of Councillors election before that.