Bond Yield vs Inflation Calculator

A bond yield vs inflation calculator computes the real yield: the purchasing-power growth a bond actually delivers once inflation is accounted for. A 5% nominal yield with 3% inflation works out to a 1.94% real yield, and in money terms 100,000 earning 5% grows to 105,000 nominal after one year, worth about 101,942 in today's purchasing power. When the real yield is negative (yield below inflation), the bond erodes purchasing power even though it still pays interest.

Run it with sensible defaults

Using nominal bond yield of 5%, expected inflation of 3%, the calculation works out to 1.94%. The defaults are meant as a starting point, not a recommendation.

The levers in this calculation

The two inputs pull in opposite directions with almost the same force. At the defaults, one percentage point of nominal yield moves the real yield by about 0.97 points, while one point of inflation moves it by about 0.98 points. Inflation carries the marginally larger lever while the real yield is positive; the two levers are exactly equal when the rates match, and once inflation exceeds the nominal yield the nominal lever becomes the larger one. Both levers shrink as inflation rises, because every effect in the Fisher division is scaled down by one plus inflation. At equal values the real yield is exactly zero: (1+x)/(1+x) − 1 = 0 whatever the rate.

How the math works

The Fisher equation divides rather than subtracts: real yield = (1 + nominal)/(1 + inflation) − 1. Division is the exact form because inflation erodes the whole final balance, principal and interest together: a 5% gain in a year when prices rose 3% buys 1.05/1.03 of last year's basket, not 1.02 of it. The familiar subtraction (yield minus inflation) appears as the Approximation row so the two can be compared directly: at 5% and 3% the shortcut says 2.00% against the exact 1.94%. The gap widens as rates rise: at a 10% yield with 20% inflation the subtraction says −10% while the Fisher division gives −8.33%, a 1.67-point difference.

Reading the result

The Assessment row applies this calculator's own illustrative bands, not an external standard. The five renderings are: 2% and above, 'Strong positive real yield'; above zero but below 2%, 'Marginal positive real yield'; exactly zero, 'Zero real yield'; below zero down to and including −2%, 'Negative real yield (mild)'; below −2%, 'Significant negative real yield (financial repression)'. Deeply negative real yields have followed large inflation spikes, as in the 1970s. Negative real yields are commonly associated with flows into riskier assets, since holding nominal bonds then preserves less purchasing power. Inflation-linked government bonds are structured so that their principal adjusts with an inflation index, which is why they behave differently from nominal bonds when real yields turn negative.

Why investors run this

A nominal yield on its own can be misleading when inflation is high: a headline 5% looks like growth, but if prices rise 7% the holding loses real value. Converting nominal to real yield puts bonds from different periods or economies on a comparable footing in purchasing-power terms.

What this doesn't capture

The calculation assumes the nominal yield and inflation rate both hold steady, which real inflation paths rarely do. It does not model uncertainty in inflation expectations, credit or default risk, liquidity, or the effect of taxes on the interest received. The output is a per-annum real rate at the two rates entered; a snapshot, not a multi-year projection or forecast.