5-year TIPS reopening Dec 2025

Bengal wrote: Sat Nov 22, 2025 5:01 pm

jeffyscott wrote: Sat Nov 22, 2025 4:59 pm

Not all schedules will mention that, here’s the full annual schedule for TIPS:

https://treasurydirect.fiscal.treasury. … ps–153869

As you can see December is a reopening.

Thanks- now back to my other thread to understand what this means.

Maybe better to keep all discussions about this in one thread, so I’ll keep my answers in this thread. From that other thread:

Bengal wrote: Sat Nov 22, 2025 6:42 pm

FactualFran wrote: Sat Nov 22, 2025 6:06 pm

The auction in December will be a re-opening of the 5-year TIPS originally auctioned two months earlier.

The only anomaly is that there will not be an official CPI-U value for the Treasury to use. Inflation-adjustments to TIPS made during December 2025 and January 2026 will use a reasonable estimate of the October 2025 CPI-U value. That does not change the daily index ratios during a month from being linear interpolations that use the Reference CPI value for the start of the month and the Reference CPI value for the start of next month.

Thanks. Doesn’t October serve as the reference CPI though, which carry the life of the bond?

What about other aspects / differences of a re-issue vs. an original auction. For example, is the index ratio approx 1.0 at re-issue, or is that carried forward from the original auction.

I was thinking of generating a “life of a TIPS” sort of tutorial, with spreadsheet calculations to illustrate every aspect. Since you’ve said that you’re an engineer and like learning from spreadsheets, would you actually open up a Google Sheets spreadsheet and look at each formula to help with your understanding?

For now, since you’re interested in the 5-year TIPS auction (a reopening) tentatively scheduled for Thursday, December 18, with settlement date 2025 Wednesday, December 31, 2025, we can focus on answering your questions specifically about that one. Another useful exercise would be to look at the auctions for a previous 5-year TIPS, to compare initial and reopening results.

First, here’s a webpage that shows the general auction frequencies for all Treasury securities: Table of Treasury Securities. Here’s the section for TIPS:

So the TIPS we’re discussing was auctioned in Oct and the reopening would be in Dec. Things that don’t change once a TIPS has been issued are dated date = 10/15/25, dated date ref CPI = 323.46710 and coupon (interest rate) = 1.125%. Things that are likely to change are unadjusted price, yield (high yield), ref CPI on issue date, and because of the latter, index ratio.

The index ratio on issue_date, 12/31/2025, depends on the ref CPI on that date, which depends on the ref CPI values for 12/1/2025 and 1/1/2026, which are equal to the CPI-U (not seasonally adjusted) values for Sep and Oct 2025. The reported value for the former was is 324.800, and based on the regulations, the value for the latter should be 325.604. Using linear interpolation (using 31 days for December), the ref CPI for 12/31/25 should be 325.57844. Therefore the index ratio should be:

= issue ref CPI / dated date ref CPI


= 325.57844 / 323.46710


= 1.00653

By comparison, the index ratio on the original issue date of 10/31/25 was 1.00148 (= 323.94606 / 323.46710).

The bid and ask prices (yields) for this TIPS on Friday when I pulled yields from Fidelity were 99.171 (1.300%), 99.195 (1.295%) respectively, compared to an unadjusted price at original auction of 99.726133 (1.182%). So the ask price now is lower and the ask yield now is higher than the price and yield at the original auction. If the TIPS were auctioned now, it would have a yield in the ballpark of the secondary market yield.

The index ratio for this TIPS on Friday was 1.00353 (for settlement on Monday 11/24/25), so IR for Monday is used), so the adjusted ask price (what you would have paid not including accrued interest ) was 99.545158 (= 99.195 * 1.00353). Since the index ratio will be higher for 12/31/25, your adjusted price would be higher if bought at auction.

All of the numbers for Friday are in the spreadsheet I’ve already shared the link to, which is quotes from Fidelity plus some of my own calculations.

I get the Treasury auction data for TIPS using IMPORTDATA with this URL:

https://api.fiscaldata.treasury.gov/services/api/fiscal_service/v1/accounting/od/auctions_query?format=csv&fields=cusip,security_term,announcemt_date,auction_date,issue_date,maturity_date,int_rate,high_yield,unadj_price,adj_price,offering_amt,adj_accrued_int_per1000,dated_date,ref_cpi_on_dated_date,ref_cpi_on_issue_date,index_ratio_on_issue_date,security_type,reopening,original_security_term,inflation_index_security&filter=inflation_index_security:eq:Yes,reopening:in:(Yes,No)&sort=-auction_date&page[number]=1&page[size]=500

I’ll pause here and let you digest this.