• Until 1873, Japan used a luni-solar calendar of 12 months (M) with 29 and 30 days (D). To align with the solar cycle an intercalary month of 29 or 30 days was added every second year, leading to varying year lengths. Annual count was done in regnal eras which, unlike Chinese tradition, were not linked with imperial accession but tied to special events.
  The Keiō era started on 01.05.1864 (JJ:D07.M04.Keiō-01) under emperor Osahito and continued under emperor Mutushito who ascended the throne on 13.02.1867 (JJ:D09.M01.Keiō-03). The era changed to Meiji on 23.10.1868 (JJ:D08.M09.Keiō-04/Meiji-1), after which the entire Keiō-4 year was rectoactively identified with the Meiji-1 year so that 25.01.1868 = JJ:D01.M01.Meiji-1.
  On 01.01.1873, Japan adopted the Gregorian calendar, so that JJ:D02.M12.Meiji-5 was followed by JJ:D01.M01.Meiji-6, since then the counting of days and months is identical in the Japanese and Gregorian calendars. The first year of an era now always coincides with the accession of a new emperor, the counting of months and days remains Gregorian. The era starts since 1868 are:
  - Yoshihito: 30.07.1912 = JJ:D30.M07.Taishō-01
  - Hirohito: 25.12.1926 = JJ:D25.M12.Shōwa-01
  - Akihito: 08.01.1989 = JJ:D08.M01.Heisei-01
  - Naruhito: 01.05.2019 = JJ:D01.M05.Reiwa-01.

Timeline

• The Tokugawa reform of 1601 established a three-currency system based on gold and silver bars and base metal coins (iron, brass), based on the weight unit (Tokugawa) ryo equal to 4.4 monme = 16.5 grams (standardized in 1891). A nominal ratio of 1 ryo gold = 7½ ryo silver = 1'500 coins existed, but the value fluctuated regionally and over time, and the gold and silver bars got debased over time. The main denominations were:
  - Gold: Koban of 1 Japanese ryo gold
  - Silver: Bu of ¼ Koban and Shu of ¹⁄₁₆ Koban, usually made from a silver-gold alloy.
• 13.05.1868
• JJ:D21.M04.Keiō-04
• Re-issuance of traditional (rectangular) coins; the Spanish Dollar got admitted for circulation at a rate of 3 Bu (silver):
  - 2 Bu: 0.8 monme (3.00 grams), ca. 20% AU / 80% AG
  - 1 Bu: 2.3 monme (8.64 grams), ca. 80% AG / 20% CU
  - 1 Shu: 0.5 monme (1.88 grams), ca. 88% AG / 12% CU
  - Tempo Tsuho (100 Bun): 5.5 monme (20.6 grams) ca. 80% CU, 20% others.
• 04.07.1868
• JJ:D15.M05.Keiō-04
• Start of issuance of state paper money of 10, 5, 1 Ryo, 1 Bu, 1 Shu for replacing the private and regional paper money.
  - 17.12.1869 (JJ:D15.M11.Meiji-02): Further issuance of state paper money with lower denominations of 2, 1 Bu, 2, 1 Shu.

Timeline

• 02.01.1871
• JJ:D12.M11.Meiji-03
• Resolution of the State Council (Daijō-kan) on the adoption of a silver currency based on the Yen with auxiliary gold and subsidiary coins in silver and copper, implementing an earlier Monetary Commissioner's decree (Ōkuma Shigenobu) of 17.03.1869 (JJ:D05.M02.Meiji-02); effective immediately.
  - Silver: 1 Yen
  - Gold: 10, 5, 2½ Yen.
• 17.01.1871
• JJ:D27.M11.Meiji-03
• Opening of the Osaka mint; coin production started on 04.04.1871 (JJ:D15.M02.Meiji-04)
• 27.06.1871
• JJ:D10.M05.Meiji-04
• Resolution of the State Council (Daijō-kan) [New Currency Ordinance, Shinkajōrei] on the adoption of the gold standard modeled after the US Dollar; effective immediately.
  - 1 Yen (gold) = 1 Ryo (gold) of the old currency, the silver Yen was restricted to use in foreign trade only.
  - Gold: 20, 10, 5, 1 Yen
  - Silver: 1 Yen at a rate of 100 Yen (silver) = 101 Yen (gold).
• 27.01.1872
• Start of coinage exchange:
  - 27.01.1872 (JJ:D18.M12.Meiji-04): Start of issuance of the new coinage
  - 05.02.1872 (JJ:D27.M12.Meiji-04): Start of issuance of government paper money (silver certificates)
  - 19.11.1896: Ordinance [No. 35] of the Ministery of Finance on the demonetization of the former subsidiary coinage (originally planned for end 1887, extended several times); effective 31.12.1896
  - 24.11.1898: Ordinance [No. 16] of the Ministery of Finance on the demonetization of the former gold and silver coinage (originally planned for end 1875, extended several times); effective 31.12.1898.
• 05.02.1872
• Start of paper money exchange:
  - 05.02.1872 (JJ:D27.M12.Meiji-04): Start of issuance of government paper money
  - 24.11.1898: Ordinance [No. 16] of the Ministery of Finance on the abolition of the demonetization of the pre-Meiji coinage; effective 31.12.1898.
• 15.12.1872
• JJ:D15.M11.Meiji-05
• Administrative agency (Daijōkan) ordinance [National Bank Act (Kokuritsu ginkō jōrei), No. 349] on the establishment of national banks and issuance of government bonds backed by gold; effective immediately (?).
  - 20.07.1876: Administrative agency (Daijōkan) ordinance [No. 106] amending the 1872 ordinance and allowing for government gold certificates (handled by Mitsui Bank Ltd); effective immediately (?).
• 28.02.1875
• Resolution of the State Council (Daijō-kan) [No. 34] on increasing the weight of the silver Yen from 416 to 420 English Troy grains silver 0.900; effective immediately.
  - 25.06.1875: Resolution [No. 108] amending No. 34 by changing the denomination to "Trade Silver (coin)" instead of "Yen"; effective immediately.
  - 04.03.1876: Resolution [No. 27], changes the parity to 100 Yen (gold) = 100 Yen (silver) / Trade Silver; effective immediately.
  - 26.11.1878: Resolution [No. 35], abolishes the trade coin and returns to the previous silver coin issuance; effective immediately.
• 25.06.1875
• Currency law [Kahei jōrei] amending the 1871 law and establishing the exchange ratios of the pre-Meiji coinage; effective immediately:
  - Gold: 100 Yen = 200 pieces of ½ Koban
  - Silver: 100 Yen = 311 pieces of 1 Bu
  - Base metal: Tenpo Tsuho (100 Bun) in copper = 8 Rin, 16 Bun in iron = 1 Rin.
• 27.06.1882
• Imperial ordinance [Nipponginkō jōrei, No. 32] on the establishment of a central bank; effective upon constitution of the bank on 10.10.1882
• 25.02.1897
• Currency law [Kaheihō] on the transition to the gold standard; effective 01.10.1897
• 02.03.1946
• Start of post-war currency exchange:
  - Deposits and cash amounts up to 100 Yen were exchanged into new currency, excess amounts were converted into state loans
  - 09.03.1946: end of exchange period and demonetization of the former banknotes.

Valuation Regimes

• 1871-1897
• Metallic currency based on circulating gold. Silver coins were initially intended for foreign trade, in 1875 they were made equivalent (de facto bimetallic standard), and in 1885, silver began dominating the circulation (de facto silver standard). Base weight was the English troy pound / 16 ounces / 480 grains at 373.242 grams.
• 1897-1917
• Fixed rate against gold; the gold standard was abandoned on 07.09.1917.
• 1930-1931
• Variable rate
• 1930-1931
• Fixed rate against gold; the gold standard was reintroduced on 11.01.1930 and abandoned again on 13.12.1931.
• 1931-1933
• Variable rate
• 1933-1945
• Fixed rate against British Pound, on 29.12.1941 nominally replace by a peg to the German Reichsmark
• 1945-1949
• No currency exchange, fixed military rate against US-Dollar
• 1949-1973
• Fixed rate against US-Dollar
• 1973-
• Variable rate