rustwood wrote: Fri Aug 29, 2025 10:08 pmMisterdan – I think it would be handy if there were an additional column with a snapshot of the current “monthly” interest thrown off by each bond. … I’m not so much interested in it per bond, but it could be handy to see the total for the portfolio. I’d probably use it to estimate interest payments per year and/or for the remainder of the year, even though they’d be rough approximations.
TIPS, like all Treasury notes and bonds, pay interest semi-annually. Currently TIPS mature on the 15th of January, February, April, July, or October. This means interest may be paid on the 15th of one of these five months or on August 15th each year. Each interest payment will equal the face value X one-half of the coupon rate X the index ratio on that date.
I’ve prepared a spreadsheet that calculates interest payments for these six dates for any specified year. (For 2025 it will show the six payments from 10/15/2024 through 8/15/2025 since we don’t yet know the index ratios for 10/15/2025.) This may help you estimate the yearly earnings of your portfolio. It’s available on the 12MoInt sheet of a Google Sheets workbook, CPI_Sheet.
Here is a snapshot of selected rows from the sheet:
Similar to my webpage, TIPS Interest & OID for 2025 , it lists every TIPS issued with an illustrative face value of $1,000. To use it, just enter the actual face value for each of your holdings and $0 for all the others. (Or you could delete those rows.) In addition, once a month you’ll need to enter the latest monthly CPI from this BLS webpage on the “CPI” sheet.
Kevin M wrote: Sun Aug 31, 2025 1:20 pm… index ratios can be retrieved directly from various sources. One way is to use the FiscalData API and the Google Sheets IMPORTDATA function with this URL:Code: Select all
https://api.fiscaldata.treasury.gov/services/api/fiscal_service/v1/accounting/od/tips_cpi_data_detail?fields=cusip,index_date,index_ratio,ref_cpi&filter=index_date:gte:2025-08-28,index_date:lte:2030-01-01,cusip:eq:91282CKL4&sort=index_date,cusip&format=csv&page[size]=10000… The latest index ratio, for 9/30/2025, … obtained with the Google Sheets formula above, is 1.04437. … The last known ref CPI is just the most recent CPI all urban consumers, not seasonally adjusted value, …
Like TreasuryDirect (e.g., 4/15/2029 TIPS/CPI Query Results), the FiscalData API only provides index ratios through the last day of the month, even though they could be calculated for one more day, e.g., 10/1/2025 instead of 9/30/2025. (That this is possible is shown on my webpage, 4/15/2029 TIPS’ 2025 Index Ratios where we see a 1.04442 index ratio for 10/1/2025.) This deficiency is most inconvenient after the October CPI is released in mid-November. It sets the Reference CPI for January 1st which determines the annual OID for TIPS held in a taxable account. But TreasuryDirect and the FiscalData API won’t report it for another month.
