TIPS Calculator: Treasury Inflation-Protected Securities Return Calculator

Treasury Inflation-Protected Securities are US Treasury bonds whose principal moves with consumer prices. The Treasury has issued them since 1997, in 5-, 10-, and 30-year terms, sold in $100 increments and backed by the same credit as any other Treasury.

The difference is where the inflation risk sits. An ordinary Treasury promises you a fixed number of dollars; whatever inflation does to those dollars is your problem. A TIPS promises you a fixed amount of purchasing power, and hands the inflation risk back to the Treasury. That is the whole product, and it explains the two features that confuse first-time buyers:

• The quoted rate looks tiny. A TIPS yield of 1.5% is not competing with a 4.3% Treasury. It is a real yield — 1.5% on top of inflation, whatever inflation turns out to be. The two numbers are quoted on different scales.
• The coupon payments grow. The rate is fixed for the life of the bond, but the principal it is charged on is not, so each payment is larger than the last in an inflationary period.

What you are buying is a floor under your purchasing power, not a higher return. In the calculator's default scenario the TIPS hands back $14,920 on a $10,000 purchase, which sounds like a 49% gain and is really a 1.5% real yield — the extra dollars exist only to keep pace with prices. The gap between those two readings of the same number is what the inflation-adjusted returns calculator measures for any investment.

Every TIPS issue carries a daily index ratio: today's reference CPI divided by the reference CPI on the day the bond was issued. Multiply your original face value by that ratio and you have the inflation-adjusted principal.

Adjusted principal = Face value × Index ratio
Semi-annual coupon = Adjusted principal × (Real yield ÷ 2)

Run the calculator's defaults through it. At 2.8% inflation the index ratio reaches 1.31805 after ten years, so $10,000 of face value becomes $13,180.48 of principal. The 1.5% coupon rate never changes, but the base it applies to does: the first payment, six months in, is $76.04, and the last one is $98.85. Add up all twenty and you have collected $1,739.53 in interest — against $1,500 if the same 1.5% had been paid on a principal that stood still.

Two details of the mechanism are worth knowing before you buy:

• The index runs about three months late.The reference CPI for a given date is built from CPI-U readings two and three months earlier, interpolated across the month. Your principal is tracking last quarter's inflation, which matters when prices turn sharply.
• Deflation cannot cut your principal below par. At maturity the Treasury repays the greater of the adjusted principal and the original face value. Set the inflation input negative and the calculator shows this floor working: the index drags the principal below $10,000, and $10,000 is still what comes back. The coupons are not floored — they follow the index down.

The compounding here is ordinary compound growth applied to a principal rather than to a return, which is why a TIPS held for thirty years at 2.8% inflation repays $22,898 on a $10,000 face value. The inflation calculator runs the same curve for money that isn't protected.

The honest comparison is not “which pays more dollars” — inflation makes that question meaningless. Both columns below start from $10,000 held for ten years: the TIPS at a 1.5% real yield, the ordinary Treasury at 4.3%, coupons spent rather than reinvested in both cases. The only thing that changes down the rows is what inflation actually turns out to be.

Read the third column first: it does not move. However bad inflation gets, the TIPS delivers $11,500 of today's purchasing power, because that is what a 1.5% real yield on $10,000 for ten years is. The dollar amount in column two swings from $11,424 to $19,974 across the same rows, and every one of those extra dollars is compensation, not gain. The one row that breaks the pattern is the deflation row at the top, where the floor under the principal pays you back more than the index says you are owed — $12,557 of purchasing power instead of $11,500.

The fourth column is the one that moves. The nominal Treasury pays the same $14,300 in every scenario, and inflation decides what that is worth — $14,300 of purchasing power if prices never rise, $8,796 if they rise 6% a year. The 4.3% Treasury is not the safer bond; it is the bond that is safe in dollars and exposed in purchasing power, while the TIPS is the reverse.

Three practical differences the table doesn't show. Tax: the annual increase in TIPS principal is federally taxable in the year it accrues, even though you collect it at maturity, so a TIPS generates a tax bill larger than its cash coupons — which is why they belong in an IRA or 401(k) when you have the room. (Both are exempt from state and local tax, as covered in the Treasury bond calculator.) Price risk: sell either bond early and you get the market price, which for a TIPS moves with real yields — 2022 saw TIPS funds lose money in the middle of an inflation spike, because real yields rose faster than the index climbed. Deflation: the first row is the case where the fixed-dollar bond wins outright, and it is not a hypothetical worth dismissing.

You do not have to guess your way through that table. One number separates the scenarios where the TIPS wins from the ones where it doesn't: the break-even inflation rate, the inflation rate at which both bonds deliver the same real return.

Break-even inflation = (1 + Nominal yield) ÷ (1 + Real yield) − 1

A 4.3% Treasury against a 1.5% TIPS breaks even at 2.76%. Subtracting the two yields gives 2.8%, close enough for a mental check but not the same number — the same distinction the Fisher equation draws between a real return and a subtracted one. Then the rule is simple:

• Inflation above 2.76% — the TIPS pays more. The index adjustment more than covers the 2.8 points of yield you gave up.
• Inflation below 2.76%— the nominal Treasury pays more. You bought insurance and the risk didn't materialize.
• Inflation at 2.76% — a tie on paper, and the TIPS still removed the uncertainty. That removal is worth something even when the arithmetic is level.

Because break-evens come out of prices real buyers are paying, they are read as the market's inflation forecast; the Federal Reserve Bank of St. Louis publishes the 10-year break-even daily. That reframes the decision usefully. Buying a TIPS is not a bet that inflation will be high — it is a bet that inflation will come in higher than the market already expects, or a decision that you would rather not be making the bet at all.

One caveat on the arithmetic. Break-even compares yields, which credits each bond for reinvesting its coupons at its own rate. If you spend the coupons instead — the assumption behind the table above — the crossover sits slightly lower, near 2.6%, because the nominal bond pays more of its return early and that head start only counts if the money is put back to work. Either way the decision rule is the same: compare the inflation you expect to the inflation priced in.