How to calculate a TIPS purchase price
A clean price of 98 does not mean a $10,000 face amount of TIPS will cost $9,800 at settlement. The quote is applied to inflation-adjusted principal, and the buyer may also owe accrued interest and fees.
The four numbers to identify
- Original face amount: the quantity of original principal you are buying.
- Clean price: the quote per $100 of face amount, excluding accrued interest.
- Settlement index ratio: the factor Treasury uses to adjust original principal for inflation.
- Accrued interest: compensation to the seller for the elapsed portion of the coupon period, calculated under the security's convention.
Use the index ratio for the actual settlement date. Treasury publishes CUSIP-specific index ratios and interest instructions. A statement's market value, an auction result and an order ticket can display different components.
A complete illustrative settlement
Assume $10,000 original face amount, a clean price of 98.00, a settlement index ratio of 1.10000, and a 2% annual coupon. For this simplified illustration, 90 days of a 180-day coupon period have elapsed. Assume no separate fee; an actual dealer spread may already be reflected in the quote.
| Step | Calculation | Amount |
|---|---|---|
| Adjusted principal | $10,000 × 1.10000 | $11,000.00 |
| Clean purchase value | $11,000 × 98 / 100 | $10,780.00 |
| Accrued interest | $11,000 × 2% / 2 × 90 / 180 | $55.00 |
| Total settlement | $10,780 + $55 | $10,835.00 |
This is an invented arithmetic example, not a current quote or an instruction to buy a security. Actual accrual uses the actual settlement date, coupon dates and day-count rules, including any unusual first coupon period.
Two common double-counting errors
If a ticket already labels interest as inflation-adjusted, do not apply the index ratio again. If it already shows the inflation-adjusted clean principal cost, do not multiply that subtotal again either.
Also check the unit: a quote or interest figure may be expressed per $100 or per $1,000, while your order may show a number of bonds. Reconcile the final cash requirement from the ticket rather than copying a displayed subtotal into the wrong unit.
Why price and yield are different
The coupon stays fixed when an existing TIPS changes hands. Its market price changes, which changes the real yield associated with the remaining cash flows. A coupon of 2% does not mean you are purchasing a 2% real yield.
To solve yield, a pricing model uses dated remaining payments and the relevant market convention. This settlement example intentionally begins with an observed clean quote; it does not estimate that quote from a Treasury par-curve yield.
What the maturity floor covers
Treasury's maturity protection concerns original principal. It does not guarantee return of your full purchase cost, including a market premium or accumulated inflation adjustment. Likewise, accrued interest paid to a seller is part of settlement, not additional original face amount.
For market-price risk, read selling TIPS before maturity. For tax basis, check the tax reference.
Use the right estimate for the task
The ladder calculator uses a simplified par-purchase model for planning. It does not perform this security-specific settlement calculation. Use its results to understand the plan's scale, then reconcile actual securities and prices before placing orders.
See how to buy TIPS for the order checklist and methodology for the model's exact assumptions.
