Average Return vs Actual Return: Why the Two Differ

Two funds can both advertise a 7% average annual return and leave you with different amounts of money. That is not marketing sleight of hand so much as a genuine ambiguity in the word average, and a return calculator will happily give you either answer depending on which box you tick.

What the calculator is actually averaging

There are two defensible ways to average a series of percentage returns, and they answer different questions.

The simple average, and where it breaks

Add the yearly returns, divide by the count. Five years of 10%, -5%, 20%, 3% and 8% sum to 36%, so the simple average is 7.2%. Clean arithmetic, and completely detached from your balance.

The problem is that percentages are applied to a shrinking or growing base. A 50% loss needs a 100% gain to get back to even, not a 50% gain. Run $100 through +50% then -50% and you hold $75, a real loss of 25% over two years, while the simple average insists you broke even. The bigger the swings, the wider that gap gets.

The compound average, or CAGR

Chain the returns instead of adding them. Take the same five years: 1.10 x 0.95 x 1.20 x 1.03 x 1.08 = 1.3949. So $10,000 became $13,949. The compound annual growth rate is the fifth root of 1.3949 minus one, which is 6.88%.

Compare that with the 7.2% simple average. Applied for five years, 7.2% would have produced $14,157, or $208 more than the account actually holds. Over five years, $208 is a rounding error. Over thirty years and a bigger balance, the same 0.32 point overstatement becomes thousands of dollars of imaginary money and quietly wrecks a retirement projection. If you want to see that effect run forward, compounding over long horizons shows how small rate differences separate.

Using the average return calculator

Enter one return per period as a percentage. Order changes neither average. Negative years go in with a minus sign, not as a positive number you plan to subtract later.

The inputs come from a fund factsheet's discrete annual performance table, or from your broker's yearly statements. Use total return figures, which include reinvested dividends, rather than price change alone. A UK equity income fund can drop 2% in price and still deliver 3% total return, and mixing the two makes the average meaningless.

Read both outputs. If the simple and compound averages are close, the return series was steady. If they are far apart, the series was volatile, and the compound figure is the only one worth quoting. The gap itself is a rough volatility reading you get for free.

When the simple average is the right tool

It is not always wrong. If you are estimating what a single future year might look like, the arithmetic mean is the better expectation, because next year's return is drawn from the distribution of years rather than from the chain of them. Forecasters use it deliberately for that reason.

For everything backward looking, use the compound figure. Anything that describes what an investment did, what a fund delivered, or what your pot grew to belongs to CAGR. Investment projection tools generally assume a compound rate as their input, so feeding one a simple average inflates the whole forecast; this walkthrough of projection inputs covers what each field expects.

Common questions

Which number do fund factsheets show? Annualised performance figures on factsheets are compound returns. The discrete year-by-year table underneath them is raw. If a document quotes a five year annualised return of 6.88%, that is CAGR, and the calculator should reproduce it from the yearly figures.

Why does my account show a different return than the fund? Because you added or withdrew money. The fund's return is time weighted and ignores cash flows. Yours is money weighted, so a large deposit made just before a bad quarter drags your personal number below the fund's published one.

Do the two averages ever agree? Only when every year's return is identical. Five straight years of exactly 7% give a simple average of 7% and a CAGR of 7%. Any variation at all pushes the compound figure below the simple one, always in that direction, never the other way.

Can a compound average be negative? Yes, and it is the honest reading when a series ends below where it started. The +50% then -50% pair gives a CAGR of -13.4% a year, which is a fair description of ending two years with $75 instead of $100.