Key Points
- Prices rose 3.7% over the 12 months ending September, up from 3.4% in August, as gasoline jumped 9.1% in a single month.
- Social Security benefits will rise 3.6% in January 2027, adding about $75 a month for the average retiree.
- September CPI sets the next I bond inflation rate at 4.08%, so bonds bought by October 31 should earn about 5.00% after their first six months.
Consumer prices rose 0.6% in September on a seasonally adjusted basis, according to the Bureau of Labor Statistics September CPI report released October 14, 2026. Over the past 12 months, the Consumer Price Index climbed 3.7%, up from 3.4% in August. The report is also the last input for Social Security’s 2027 COLA and the next I bond interest rate.
Gasoline was the biggest driver of the increase. The gas index rose 9.1% in September and accounted for more than half of the monthly increase. Energy prices overall are now up 20.4% from a year ago. Core inflation, which strips out food and energy, rose 0.3% for the month and 2.6% for the year.
Why It Matters
Higher prices are shrinking what cash actually earns. Top high-yield savings accounts pay around 4% APY, leaving savers with less than half a point of real return after 3.7% inflation. While higher rates are a boost to savers, it’s still hard to outearn inflation. Groceries were the bright spot, falling 0.1% in September and rising just 1.8% over the year.
Retirees get some relief next year. The Social Security Administration announced a 3.6% COLA for 2027 the same morning, which adds about $75 a month to the average retirement benefit starting in January. That increase is tied to the CPI-W, a version of the Consumer Price Index that tracks wage earners and clerical workers.
What It Means For I Bonds
September CPI locks in the inflation portion of the next I bond rate. Treasury measures the change in CPI-U from March to September, and the index rose from 330.213 in March to 336.940 in September. That works out to a 2.04% six-month increase, or 4.08% annualized, up from the 3.34% rate on bonds issued since May. Here’s how that plays out under Treasury’s composite rate formula:
- Bonds bought by October 31 lock in today’s 0.90% fixed rate, earning 4.26% for six months and then about 5.00%.
- A November purchase gets the 4.08% inflation portion plus whatever new fixed rate Treasury announces November 1.
- Older bonds pick up the 4.08% inflation rate at their next six-month reset, on top of their own fixed rate.
How This Connects
Education prices rose 0.6% in September and 3.8% over the past year, slightly ahead of overall inflation for families already facing a high average cost of college.
Borrowers feel inflation through rates as well. Federal student loan interest rates are set each May from the 10-year Treasury yield, so higher yields next spring would mean higher rates on 2027-28 federal student loans.
What’s Next
The Federal Reserve meets October 27-28 with this report in hand. Treasury announces new I bond rates November 1, and BLS publishes October CPI on November 10. Savers parking cash ahead of those dates can compare today’s best savings rates.
Editor: Colin Graves
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