 How the “Ref Index” and “Indexation Coefficient” applicable to InflationIndexed Bonds are calculated.
(n: calendar day corresponding to the date of calculation, m: month to which the n^{th} day belongs)
< Ref Index >
Ref Index corresponds to the following (rounded to the third decimal place) :
(1) If n=10,
CPI^{[1]} for the (m3)^{th} month
(2) If n>10,
Ref Index for the 10^{th} day of the m^{th} month  +  (  Ref Index for the 10^{th} day of the (m+1)^{th} month  −  Ref Index for the 10^{th} day of the m^{th} month  )  ×  (n−10) 
the number of days from the 11^{th} day of the m^{th} month to the 10^{th} day of the (m+1)^{th} month 
(3) If n<10,
Ref Index for the 10^{th} day of the (m−1)^{th} month  +  (  Ref Index for the 10^{th} day of the m^{th} month  −  Ref Index for the 10^{th} day of the (m−1)^{th} month  )  ×  the number of days from the 11^{th} day of the (m−1)^{th} month to the n^{th} day of the m^{th} month 
the number of days from the 11^{th} day of the (m−1)^{th} month to the 10^{th} day of the m^{th} month 
< Indexation Coefficient >
Indexation Coefficient corresponds to the following (rounded to the fifth decimal place ^{[2]}) :
Ref Index for the n^{th} day of the m^{th} month 
Ref Index for the 10^{th} day of the issue month (interest payment month) ^{[3]} 
[1] CPI means the Japan Consumer Price Index, which represents the general consumer price index excluding fresh food.
[2] Indexation Coefficient for InflationIndexed Bonds issued before 31^{st} March 2016 should be rounded to third decimal place.
[3] When the period from the issuance to the first interest payment is less than 6 months, “the issue month” should be replaced by the month 6 months before the first interest payment month, in calculating the inflationadjusted principal amount.
In case of the reopened issue, Ref Index for the 10^{th} day of the issue month of the outstanding issue should be applied.
* The 2020base revision of CPI
2015base CPI was revised to 2020base CPI in August 2021.
Calculation method of Indexation Coefficient after 11^{th} September 2021 is as follows:
Note that Ref Index and Indexation Coefficient before 10^{th} September 2021 which was already calculated based on old base CPI will not be modified by the 2020base revision of CPI.
Issue number 17 to 21
Before 10^{th} Sep 2021  After 11^{th} Sep 2021  


(note 1) To calculate Ref Index for the 11^{th} Sep 2021 to the 9^{th} Oct 2021, Ref Index for the 10^{th} Sep 2021 (2020base) should be used. (note 2) A fraction is to be rounded off finally in calculation. 
Issue number 22 to 26
Before 10^{th} Sep 2021  After 11^{th} Sep 2021  


(note 1) To calculate Ref Index for the 11^{th} Sep 2021 to the 9^{th} Oct 2021, Ref Index for the 10^{th} Sep 2021 (2020base) should be used. (note 2) A fraction is to be rounded off finally in calculation. 
Provisional calculations of Ref Indices and Indexation Coefficients by the MOF. *
* These figures are offered for your information only. Their authenticity should be scrutinized if they are used for the sake of transactions.