The U.S. Bureau of the Fiscal Service announced that Series I savings bonds purchased from May 1 through October 31, 2026, will earn a 4.26% composite annual rate. That rate combines a 0.90% fixed component with a 1.67% semiannual inflation adjustment, giving savers a return that sits well above most high-yield savings accounts but below the peaks I bonds reached in recent years. For the roughly ten million Americans who hold I bonds through TreasuryDirect, the new rate resets the math on whether to buy more, hold, or redirect cash elsewhere.
How the 4.26% I Bond Rate Stacks Up Against Alternatives
The 4.26% composite rate reflects six months of consumer price changes. The Bureau of Labor Statistics published CPI-U readings that Treasury used as inputs: the index rose from 324.8 in September 2025 to 330.213 in March 2026, according to the Fiscal Service announcement. That 1.67% semiannual gain, annualized to roughly 3.36%, is then layered on top of the 0.90% fixed rate to produce the headline figure.
The distinction between those two components matters for anyone deciding where to park cash. The fixed rate locks in for the life of the bond, while the inflation piece resets every six months based on fresh CPI-U data. A saver who buys today keeps the 0.90% floor even if inflation drops to zero in a future period. By contrast, a six-month Treasury bill purchased on the secondary market offers a yield that disappears entirely at maturity, with no built-in inflation hedge. That gap between the I bond’s composite rate and short-term T-bill yields, rather than the raw inflation number itself, is what tends to drive purchase volume. When I bonds clearly beat risk-free alternatives on an after-tax, inflation-adjusted basis, demand spikes. When the gap narrows, buyers pull back.
Compared with online savings accounts and money market funds, the 4.26% rate is competitive but not a slam dunk. Bank products offer daily liquidity and no penalty for withdrawals, while I bonds cannot be redeemed at all in the first 12 months and carry a three-month interest penalty if cashed in before five years. For savers who already maintain an emergency fund elsewhere, however, the extra yield and inflation protection can justify those trade-offs.
CPI-U Inputs and the Regulatory Formula Behind the Rate
Treasury does not set I bond rates by committee vote or market auction. The composite rate follows a formula codified in 31 CFR Part 359, which prescribes how the fixed rate and inflation rate combine. The semiannual inflation rate of 1.67% is derived directly from the percentage change in CPI-U between September 2025 and March 2026. The BLS published the September 2025 figure in its October 2025 release and the March 2026 figure in its April 2026 release, giving Treasury two clean data points six months apart.
The inflation component is calculated as the percentage increase in CPI-U over that six-month window, rounded to two decimal places. Treasury then doubles that semiannual figure to annualize it and plugs it into the composite formula: fixed rate plus twice the inflation rate, plus a small interaction term that reflects compounding. The result is rounded to the nearest one-hundredth of a percent to produce the posted 4.26% rate. As outlined on Treasury’s page explaining I bond interest calculations, the inflation component can never drive the composite rate below zero, even in a period of deflation.
Series EE bonds, the other savings bond still sold through TreasuryDirect, were simultaneously set at 2.40% for the same May-through-October window. That rate is not inflation-adjusted and carries a different value proposition: EE bonds are guaranteed to double if held for 20 years, effectively locking in a 3.5% annualized return over that horizon regardless of what happens to prices. For savers with shorter time frames, the I bond’s 4.26% rate is the more relevant number, but the two products serve different planning goals.
Who Should Consider Buying at the New Rate
Because the 0.90% fixed rate is locked in for the life of any bond purchased in this window, the current offering is most attractive to long-term holders who expect inflation to remain at least moderate. A higher fixed rate means that even if inflation cools, the bond will continue to earn a baseline real return. Investors who skipped earlier cycles with lower fixed rates may view the current terms as a chance to build a core position.
That said, I bonds are not ideal for every purpose. Annual purchase limits-typically $10,000 per person electronically, plus up to $5,000 via paper bonds with a tax refund-cap how much cash can be shifted into the program each year. The one-year lockup also makes I bonds a poor fit for near-term spending needs such as tuition due within months or an upcoming home purchase. Treasury’s overview of I bond features emphasizes that they are designed as a conservative, long-term savings tool rather than a trading vehicle.
For households deciding whether to buy now or wait, the key variables are inflation expectations and the possibility of future fixed-rate changes. If inflation accelerates, the bonds purchased at today’s terms will see their composite rate adjust upward every six months. If inflation falls sharply, the 0.90% fixed rate will look more valuable relative to new issues sold at potentially lower fixed rates. Because no one can reliably time those moves, many savers choose to spread purchases over multiple years, gradually building a ladder of bonds with different fixed-rate vintages.
Ultimately, the 4.26% composite rate will not recreate the frenzy that surrounded I bonds when inflation surged earlier in the decade, but it does restore the product’s relevance in a more normal environment. For investors seeking government-backed protection against unexpected price increases, the current terms offer a balanced mix of yield, safety, and flexibility within the program’s limits.
