Choosing a Return Assumption

Be hopeful enough to plan — humble enough to survive

The return field is where optimism sneaks into a plan. Nudge it from 7% to 10% and a difficult goal suddenly looks achievable, which is exactly why it deserves more scrutiny than any other input on the page.

Anchor the rate to what you own

A portfolio of broad stock index funds has historically averaged somewhere around 10% before inflation and roughly 7% after it. Either is defensible as long as you know which one you used.

A balanced mix holding a meaningful share of bonds will run lower, often in the 5% to 6% range, because bonds trade return for stability.

A target-date fund shifts over time, starting stock-heavy and getting more conservative as the date approaches. Model it a point or two below a pure stock assumption if your date is close.

Key points

Stock-heavy portfolio: 7% is a reasonable planning figure.
Balanced portfolio: 5% to 6% fits better.
Conservative or near-term money: 3% to 4%.
Above 10% as a long-run default is not a plan.
Always subtract your fund expenses from whatever you choose.

Run a band, not a point

Pick three rates — a pessimistic one, your best guess, and an optimistic one — and run the same contribution and horizon through all three.

The three endings define the territory your plan might land in. That range is far more honest than a single number carried to the dollar.

If the pessimistic run still gets you somewhere acceptable, you have a plan. If only the optimistic run works, you have a hope dressed up as a plan.

Key takeaway Choose a return you would defend to a skeptic, then check what happens if you are wrong by two points. A plan that only survives the optimistic case is not really a plan.

Nominal versus real

Historical stock averages are usually quoted before inflation. If you use a nominal rate, your ending balance is in future dollars that buy less than today's.

You can handle this two ways: model at the nominal rate and inflate your goal to match, or model at a real rate around 7% and read the result in today's purchasing power.

Either approach works. Mixing them — projecting nominal and spending as if it were real — is what quietly breaks long-term plans.

Subtract your costs before you finalize the number

Whatever rate you settle on describes the market, not your account. Your account also pays fund expenses, and possibly an advisory fee, and those come out every year regardless of performance.

Look up the expense ratio on each fund you own. A broad index fund might charge 0.03% to 0.10%, which is small enough to ignore, while an actively managed fund charging 0.75% is not.

Subtract the total from your assumed return before you run the projection. If you expect 7% and pay 1% in combined costs, you should be modeling 6%.

This one adjustment is the difference between a projection you can trust and one that quietly overstates your ending balance by a meaningful margin over a long horizon.

Revisit without overreacting

Your assumption should change when your portfolio changes, not when the market has a dramatic year. A great year does not justify raising your long-run estimate.

Check once a year at most, and only adjust if your actual holdings have shifted meaningfully.

Frequent adjustment turns a planning tool into a mood ring, which produces worse decisions than leaving a slightly imperfect number alone.

                    The honest default: when you genuinely do not know, use 6%. Being pleasantly surprised beats discovering at 55 that your plan required a decade nobody got.
                

Try these inputs

Pessimistic: $0 start, $300/mo, 4%, 25 years
Best guess: $0 start, $300/mo, 7%, 25 years
Optimistic: $0 start, $300/mo, 9%, 25 years

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