- How the “Ref Index” and “Indexation Coefficient” applicable to Inflation-Indexed Bonds are calculated.
(n: calendar day corresponding to the date of calculation, m: month to which the nth day belongs)
< Ref Index >
Ref Index corresponds to the following (rounded to the third decimal place) :
(1) If n=10,
CPI[1] for the (m-3)th month
(2) If n>10,
| Ref Index for the 10th day of the mth month | + | ( | Ref Index for the 10th day of the (m+1)th month | − | Ref Index for the 10th day of the mth month | ) | × | (n−10) |
| the number of days from the 11th day of the mth month to the 10th day of the (m+1)th month |
(3) If n<10,
| Ref Index for the 10th day of the (m−1)th month | + | ( | Ref Index for the 10th day of the mth month | − | Ref Index for the 10th day of the (m−1)th month | ) | × | the number of days from the 11th day of the (m−1)th month to the nth day of the mth month |
| the number of days from the 11th day of the (m−1)th month to the 10th day of the mth month |
< Indexation Coefficient >
Indexation Coefficient corresponds to the following (rounded to the fifth decimal place) :
| Ref Index for the nth day of the mth month |
| Ref Index for the 10th day of the issue month (interest payment month) [2] |
[1] CPI means the Japan Consumer Price Index, which represents the general consumer price index excluding fresh food.
[2] 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 inflation-adjusted principal amount.
In case of the re-opened issue, Ref Index for the 10th day of the issue month of the outstanding issue should be applied.
* The 2025-base revision of CPI
2020-base CPI was revised to 2025-base CPI in August 2026.
Calculation method of Indexation Coefficient after 11th September 2026 is as follows:
Note that Ref Index and Indexation Coefficient before 10th September 2026 which was already calculated based on old base CPI will not be modified by the 2025-base revision of CPI.
Issue number 22 to 26
| Before 10th Sep 2026 | After 11th Sep 2026 | |||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
|
(note 1) To calculate Ref Index for the 11th Sep 2026 to the 9th Oct 2026, Ref Index for the 10th Sep 2026 (2025-base) should be used. (note 2) A fraction is to be rounded off finally in calculation. |
Issue number 27 to 31
| Before 10th Sep 2026 | After 11th Sep 2026 | |||||||
|---|---|---|---|---|---|---|---|---|
|
(note 1) To calculate Ref Index for the 11th Sep 2026 to the 9th Oct 2026, Ref Index for the 10th Sep 2026 (2025-base) 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.
