The Mutan interest rate is the Uncollateralised Overnight Call Rate in Japan. It is the reference rate for JPY overnight unsecured transactions in the Japanese market. It was launched in April 1996 and it is the main tool for the transmission of the Bank of Japan's monetary policy.
Publication
Bank of Japan publishes a provisional rate, rounded to three decimal places, every business day around 17:15 JST (or 18:15 JST for the last business day of the month). A final result is published the following business day around 10:00 JST. The results published contain weighted-average, highest, and lowest rate during the business day.
References
Mutan rate Wikipedia(Text) CC BY-SA