Real investment return:
formula and worked example

Why a 9% return is not a 9% gain in what you can buy

A bank statement reports nominal growth: how many more rupees you have. What most people actually care about is whether those rupees buy more than before. If prices rise while your money grows, part of the gain is only keeping pace. The real return strips that part out and reports the improvement in purchasing power.

This matters most over long horizons and in periods of higher inflation. An investment that looks comfortably positive on paper can be flat or negative once the cost of living is allowed for, which changes how much you need to save to reach a goal fixed in today's money, such as a child's education fee or a retirement income.

It also keeps comparisons honest across countries and eras. A 9% return means something very different where inflation is 2% than where it is 8%, and only the real figure puts both on the same footing.

Use it to judge whether an asset is actually protecting and growing your wealth, rather than only whether its number went up.

The exact formula, and why subtracting is only an approximation

• Nominal: the investment's return over the period, before adjusting for prices, as a decimal.
• Inflation: the rise in the general price level over the same period, as a decimal.

Many people simply subtract inflation from the nominal return. That shortcut is close at low rates but is not exact, because your money and the price level both grow multiplicatively. The division form above is the correct relationship, and the gap between the two widens as rates climb.

Worked example: 9% nominal with 5% inflation

1. 1Add 1 to the nominal return to get the growth factor: 1 + 0.09 = 1.09.
2. 2Add 1 to inflation to get the price factor: 1 + 0.05 = 1.05.
3. 3Divide growth by prices: 1.09 ÷ 1.05 ≈ 1.038095.
4. 4Subtract 1 and multiply by 100: about 3.81%.

In money you can feel: 100,000 grows to 109,000. A basket of goods that cost 100,000 now costs 105,000. Measured in today's goods, your 109,000 is worth about 103,810, so the true gain is 3,810 rather than 9,000.

What a real return tells you, and when it turns negative

A positive real return means your wealth buys more than it did. Zero means you only kept pace. A negative figure means your money lost purchasing power even though the account balance went up. That last case is far more common than people expect with low-yielding deposits held through a period of high inflation.

Take 9% nominal against 12% inflation. The factor is 1.09 ÷ 1.12 ≈ 0.9732, a real return of about −2.68%, where subtraction would have said −3%. Here the account balance grows by 9,000 per 100,000 invested while the real value of the money falls by about 2,680.

The takeaway is that inflation is a quiet cost rather than a charge you see. Nothing is deducted from the account, which is why many savers underestimate it. The formula makes that hidden cost visible and puts a number on it.

How the real return responds when the nominal return moves

In the table, the nominal return rises from 9% to 9.9%, a 10% relative increase, with inflation fixed at 5%.

The nominal return improved by 0.9 percentage points and the real return by about 0.86, which is that 0.9 divided by the 1.05 price factor. So a point of extra nominal return is worth slightly less than a point of real return. Inflation, meanwhile, works against you the same way in reverse: raising inflation from 5% to 6% in this example would cut the real return to about 2.83%.

Frequent slips when adjusting for inflation

• Using the wrong period. A five-year return must be matched with five-year inflation, not a single year's rate.
• Entering whole percentages. 9 instead of 0.09 turns the formula into nonsense; both must be decimals.
• Using a headline inflation figure that does not match your spending. Your personal inflation can differ from the general index.
• Forgetting tax and costs. The formula uses the return you actually receive after charges and tax, since those erode purchasing power too.

When inflation is running at several percent, even the choice between two deposits matters more than it seems. A deposit paying 6% in an economy with 5% inflation is only adding about 0.95% in real terms, while the headline suggests six times that.

Using the real return to plan a goal

If a target is expressed in today's money, plan with the real return rather than the nominal one. A saver expecting 9% nominal and assuming 5% inflation should plan around about 3.8% real growth, which gives a more honest picture of what the goal will cost to fund. Doing so avoids the common surprise of reaching a target on paper and finding it no longer buys what it did when you set it.

1. 1Estimate a nominal return for the instrument, net of charges.
2. 2Choose an inflation assumption for the whole holding period.
3. 3Convert to a real return using the division form.
4. 4Project the goal in today's money using the real rate, and save accordingly.