May 2026 CPI 335.123: TIPS Reference CPI for July and August
The Bureau of Labor Statistics reported the May 2026 CPI-U, all items, not seasonally adjusted, at 335.123 (1982 to 1984 = 100). That is a rise of 0.63% from April 2026 and 4.25% above May 2025. This not seasonally adjusted series is the one the Treasury uses to adjust TIPS principal, so the headline seasonally adjusted number in news reports will differ.
The TIPS reference CPI for any day uses the CPI from three months earlier, interpolated toward the value from two months earlier. The May 2026 print fixes every daily reference CPI in July 2026 and the value on August 1, 2026. TIPS principal in May 2026 does not depend on the May 2026 print.
Reference CPI values this print sets
| Date | Reference CPI | Derived from |
|---|---|---|
| July 1, 2026 | 333.02000 | April 2026 CPI |
| July 15, 2026 | 333.96974 | interpolated, day 15 of 31 |
| July 31, 2026 | 335.05516 | interpolated, day 31 of 31 |
| August 1, 2026 | 335.12300 | May 2026 CPI |
Effect on principal
From July 1, 2026 to August 1, 2026, the reference CPI moves up by 0.631%. Every TIPS carries the same index ratio change over those dates, so $10,000 of inflation-adjusted principal on July 1, 2026 becomes about $10,063 on August 1, 2026, before any coupon. A holder in a taxable account owes tax on that principal change for the year even though no cash is paid. See phantom income.
The last 12 months
| Month | CPI-U (NSA) | Change | Sets reference CPI for |
|---|---|---|---|
| May 2026 | 335.123 | +0.63% | July 2026 through August 1, 2026 |
| April 2026 | 333.020 | +0.85% | June 2026 through July 1, 2026 |
| March 2026 | 330.213 | +1.05% | May 2026 through June 1, 2026 |
| February 2026 | 326.785 | +0.47% | April 2026 through May 1, 2026 |
| January 2026 | 325.252 | +0.37% | March 2026 through April 1, 2026 |
| December 2025 | 324.054 | -0.02% | February 2026 through March 1, 2026 |
| November 2025 | 324.122 | n/a | January 2026 through February 1, 2026 |
| September 2025 | 324.800 | +0.25% | November 2025 through December 1, 2025 |
| August 2025 | 323.976 | +0.29% | October 2025 through November 1, 2025 |
| July 2025 | 323.048 | +0.15% | September 2025 through October 1, 2025 |
| June 2025 | 322.561 | +0.34% | August 2025 through September 1, 2025 |
| May 2025 | 321.465 | +0.21% | July 2025 through August 1, 2025 |
The BLS published no value for October 2025, so the month is absent from the table and the following month shows no change figure.
Why the three-month lag exists
The Treasury needs a published index value before it can adjust principal, and the BLS publishes each month's CPI about two weeks after the month ends. Using the value from three months earlier and interpolating day by day gives every settlement date a known reference CPI in advance. The lag means TIPS principal always reflects inflation from a few months back, which matters most when inflation changes direction quickly. How TIPS principal and interest work explains the mechanics. The price calculation shows where the index ratio enters a settlement amount.
Sources: BLS series CUUR0000SA0, BLS Consumer Price Index, TreasuryDirect TIPS and CPI data, and the formula in 31 CFR 356, Appendix B. The May 2026 value was first saved by this site on September 11, 2026. Reference CPI figures here are computed from the published index and rounded to five decimals. Treasury's published table governs.
