Nominal vs Real Return: What Future Dollars Can Buy

Treat the dollar date as a unit

A future nominal balance is the number of dollars at that future date. A today-dollar balance expresses its purchasing power relative to today’s price level. The two can describe the same account, just as two units can describe the same physical distance.

BLS explains constant-dollar conversions using price-index ratios. MoneyBasis uses a simpler planning assumption: one selected inflation rate repeated over the horizon. For a future amount F, annual inflation i and t years, today-dollar value is F ÷ (1 + i)^t. This does not predict the path of an actual price index.

Calling an amount “real” also does not make it after-tax or freely spendable. Taxes, withdrawal restrictions and transaction costs are separate considerations. The label means inflation-adjusted only unless additional adjustments are explicitly named.BLS

Why subtracting inflation is only an approximation

If an investment grows by an effective 7% over a year while prices rise 3%, the purchasing-power growth factor is 1.07 ÷ 1.03. Subtract one to get a real return of 3.8835%. Subtracting 3% from 7% gives a nearby 4%, but not the exact result.

The exact relationship uses growth factors because the investment value and the price of goods both change. Dividing those factors compares how many units of goods can be bought afterward. The simple subtraction r − i is a convenient approximation when rates are small; it is not an identity.

Both rates must refer to the same period. The nominal return in this relationship is the effective return over that period, not necessarily the nominal annual rate entered into a compounding calculator. A nominal rate compounded monthly must first be converted to its effective annual factor before being compared with annual inflation.CFPB

Worked example

Worked example: one account, two views

Start with $10,000 and no further deposits. Assume 7% growth compounded annually for ten years and constant annual inflation of 3%. The nominal future value is $19,671.51. Divide by 1.03^10 and the same balance is $14,637.45 in today’s purchasing power.

Both lines begin at $10,000 because today’s dollars and nominal dollars coincide at the starting date. They separate as the assumed price level rises. The gap does not represent cash removed by a bank; it reflects the change in what each dollar buys.

The nominal balance can rise even when purchasing power falls. That happens when the effective investment growth factor is smaller than the inflation factor. A nominal gain alone therefore cannot establish that a future spending goal has become easier to fund.

Put the goal and the balance on the same basis

A target expressed in today’s prices needs to be moved forward before comparison with a future nominal account balance. Under 3% constant inflation, $10,000 today becomes $13,439.16 after ten years. Alternatively, the future account balance can be brought back to today’s dollars. Either method works when applied consistently.

MoneyBasis’s retirement calculator takes desired monthly spending in today’s dollars, inflates it to retirement, and then increases nominal spending annually during retirement. Its future portfolio balance remains nominal. Comparing that future balance directly with today’s spending without the conversion would understate the future dollar requirement when assumed inflation is positive.

The savings-goal calculator takes a nominal future target. It does not perform this inflation adjustment automatically. The compound-interest calculator can show both nominal future value and an inflation-adjusted value when an inflation assumption is entered. These different interfaces can be consistent because each names the basis it uses.

One inflation rate cannot describe every household

An inflation index summarizes a basket, while a household’s spending mix may put more weight on housing, health care, travel or another category. A specific goal can also have a price that changes differently from the general price level. The conversion is only as relevant as the assumed rate and spending definition.

The illustration uses constant rates and has no deposits, taxes or fees. Actual investment returns and inflation vary over time. A one-period real-return formula remains valid for matching measured periods, but a long-term scenario using one constant rate does not show that variation.

Useful labels name both the date and the basis: “future nominal balance” or “today-dollar purchasing power.” Avoid adding those two versions together or treating the inflation-adjusted number as a second asset.