The U.S. Treasury today finally announced a calculated CPI index for October – 325.604 – which equates to monthly inflation of 0.25%. The presumed annual rate ticked higher from 3.0% in September to 3.1% in October.
This unprecedented calculation was necessary because no inflation data were collected in October during the 43-day government shutdown. Without that data, Treasury had to determine a number so that daily inflation indexes could be set for Treasury Inflation-Protected Securities during the month of December.
For nerds: That 0.25% number (actually 0.248% before rounding) reflects an estimate of non-seasonally-adjusted inflation. It is not the seasonally-adjusted number the Bureau of Labor Statistics reports each month, which gets rounded to the tenth-decimal point. In this case that would be 0.2%, but … not relevant.
The calculation procedure is set out in the Treasury’s Uniform Offering Circular (Appendix B to 31 CFR Part 356), which says:
If the CPI for a particular month is not reported by the last day of the following month, we will announce an index number based on the last available twelve-month change in the CPI. We will base our calculations of our payment obligations that rely on that month’s CPI on the index number we announce.
For example, if the CPI for month M is not reported timely, the formula for calculating the index number to be used is:
If it is necessary to use these formulas to calculate an index number, we will use that number for all subsequent calculations that rely on the month’s index number. We will not replace it with the actual CPI when it is reported, except for use in the above formulas. If it becomes necessary to use the above formulas to derive an index number, we will use the last CPI that has been reported to calculate CPI numbers for months for which the CPI has not been reported timely.
What this all means, basically, is that the Treasury looked back at the average inflation rate of the last 12 months (September 2024 to September 2025) and used the formula to remove any effect of compounding. That calculation resulted in an inflation index of 325.604 and a monthly increase of 0.25%.
October’s inflation index will forever be 325.604, whether right or wrong. I’d guess the 0.25% monthly increase was close, but we will never know for sure. The November inflation report will arrive on December 18.
This calculation was crucial because inflation in October sets inflation indexes for TIPS in the month of December. Here are the December Inflation Ratios for all TIPS, which were released immediately after the calculated October CPI was announced.
As future inflation data are collected, the missing October data will become less crucial as new reports reflect price reality. There won’t be any meaningful effect on I Bonds, because the October number is the first of a 6-month string that will determine the I Bonds next variable rate, to be reset May 1. That will autocorrect.
One interesting factor for TIPS held in a traditional retirement account, however, is that the December numbers are highly likely slightly off, but required minimum distributions will be set by the value of TIPS on December 31. I’d contend this isn’t a huge deal, but some of my more OCD readers will be disturbed.
I am glad this saga is over so I can stop checking the Treasury website five times a day to see if the official October number was released.
Enjoy your Thanksgiving everyone!
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Author of Tipswatch.com blog, David Enna is a long-time journalist based in Charlotte, N.C. A past winner of two Society of American Business Editors and Writers awards, he has written on real estate and home finance, and was a founding editor of The Charlotte Observer's website.
I have a timely question. When the ACA subsidies expire at the end of the year, the cost of healthcare for over 24 million people will double or more. But in the inflation calculation, is it true that the increase in healthcare cost will exclude the out of pocket increase due to the expiration of the subsidies and only tally the increase in healthcare cost itself? And if so, does that mean inflation is under-counting real inflation on real people?
Hi David, this is Amy again. I commented on a post of yours in the past detailing my experience with TreasuryDirect, how they sent my I-bond redemption to Pathward bank to an unauthorized user instead to me at my correct bank account. I lost all of my money. I found more victims, complained to various federal agencies, there are various reddit threads about this topic, and also Suze Orman mentioned this situation on her latest podcast (around 15 minute mark, it’s on Spotify). I am wondering if you’d consider writing an article about this to help myself and other victims raise awareness.
Thanks for keeping us informed and Happy Thanksgiving. Somehow an unprecedented synthetic inflation report seems appropriate for 2025 America in the era of AI. Hopefully we won’t have to go through this again in 2026 but never say never.
You wrote “The U.S. Treasury today finally announced a calculated CPI index for October – 325.604 – which equates to monthly inflation of 0.25%. The presumed annual rate ticked higher from 3.0% in September to 3.1% in October.” However, those numbers — 325.604 and 3.1% October inflation — are not mentioned in the linked press release.
Where did you find those number? Did you calculate them yourself? If so, what were the CPI-W and Chained CPI numbers for October?
The release did say this: “The index number for October 2025 is 325.604.” I just plugged that into my Inflation and I Bonds chart and got the monthly increase of 0.25% and Oct to Oct increase of 3.1%. https://tipswatch.com/tracking-inflation-and-i-bonds/
You can use the numbers there to double-check my calculation. I saw no information on other CPI numbers. Of course, BLS rounds to the 10th decimal point in its official reports.
Treasury Inflation-Protected Securities 
I have a timely question. When the ACA subsidies expire at the end of the year, the cost of healthcare for over 24 million people will double or more. But in the inflation calculation, is it true that the increase in healthcare cost will exclude the out of pocket increase due to the expiration of the subsidies and only tally the increase in healthcare cost itself? And if so, does that mean inflation is under-counting real inflation on real people?
Hi David, this is Amy again. I commented on a post of yours in the past detailing my experience with TreasuryDirect, how they sent my I-bond redemption to Pathward bank to an unauthorized user instead to me at my correct bank account. I lost all of my money. I found more victims, complained to various federal agencies, there are various reddit threads about this topic, and also Suze Orman mentioned this situation on her latest podcast (around 15 minute mark, it’s on Spotify). I am wondering if you’d consider writing an article about this to help myself and other victims raise awareness.
Some anecdotal evidence: I heard on a podcast was that for Black Friday, sales in terms of quantity was down 1% but prices were up 7%.
Happy Thanksgiving, David and all. Thank you for all your yearly work helping us stay abreast.
Thanks for keeping us informed and Happy Thanksgiving. Somehow an unprecedented synthetic inflation report seems appropriate for 2025 America in the era of AI. Hopefully we won’t have to go through this again in 2026 but never say never.
You wrote “The U.S. Treasury today finally announced a calculated CPI index for October – 325.604 – which equates to monthly inflation of 0.25%. The presumed annual rate ticked higher from 3.0% in September to 3.1% in October.” However, those numbers — 325.604 and 3.1% October inflation — are not mentioned in the linked press release.
Where did you find those number? Did you calculate them yourself? If so, what were the CPI-W and Chained CPI numbers for October?
The release did say this: “The index number for October 2025 is 325.604.” I just plugged that into my Inflation and I Bonds chart and got the monthly increase of 0.25% and Oct to Oct increase of 3.1%. https://tipswatch.com/tracking-inflation-and-i-bonds/
You can use the numbers there to double-check my calculation. I saw no information on other CPI numbers. Of course, BLS rounds to the 10th decimal point in its official reports.
Whoops, mybad. I see it now.
Happy Thanksgiving!
FYI, I tried that crazy CPI calculator and actually came up with 325.604 for CPI-U. For CPI-W it was 318.909 and for Chained CPI it was 180.537.
Thank you, David. Happy Thanksgiving to you!
’Synthetic’ is an apt description. Thank you for all your updates – and happy Thanksgiving! 🦃