The CPI-U value increased from March's value of 229.392 to September's value of 231.407, resulting in a semi-annual adjustment of 0.88%. Since we now know the inflation-linked rate of the I Bond rate for November, we can calculate the possible new rates. The fixed rate portion of the new rate will not be known until November 1.
CPI-I values for March - September
Possible November I Bond rates
CPI-I values for March - September
| March | April | May | June | July | Aug. | Sept. |
| 229.392 | 230.085 | 229.815 | 229.478 | 229.104 | 230.379 | 231.407 |
Possible November I Bond rates
| Theoretical Fixed Rate | Composite Rate |
| 0.00% | 1.76% |
| 0.10% | 1.86% |
| 0.20% | 1.96% |
| 0.30% | 2.06% |
| 0.40% | 2.16% |
| 0.50% | 2.26% |
| 0.60% | 2.37% |
| 0.70% | 2.47% |
| 0.80% | 2.57% |
| 0.90% | 2.67% |
| 1.00% | 2.77% |
| 1.10% | 2.87% |
| 1.20% | 2.97% |
| 1.30% | 3.07% |
| 1.40% | 3.17% |
Since the fixed rate has remained at 0% for 2 years now, I strongly suspect it will remain there, resulting in a 1.76% composite rate for new I bonds sold in November. Since the fixed rate can't decrease, there is no benefit to buying I Bonds now or after the November 1 rate change.
