RESEARCH · 5 OCTOBER 2026 · REPRODUCIBLE WORKED EXAMPLE

Same portfolio. Different assumption. Different saving decision.

Choosing an expected return can feel like choosing a fact. It is a judgement. A more useful question is how much your plan changes if that judgement is wrong.

The decision behind the number

The reference portfolio’s modelled annual compound growth is 6.23% before fees. Reducing it by two percentage points produces 4.23%. With a 0.3% annual fee and 2.5% inflation, the reference ends at $201,923 in today’s purchasing power; the alternative ends at $171,792.

For a $300,000 target in today’s money, the implied monthly saving rises from $1,276 to $1,623. That does not mean anyone must save that amount. It makes the trade-off visible: revise saving, timing, spending expectations or the investment plan rather than relying on one favourable return.

Currency changes the assumptions

These are five separate illustrative investors, each starting with 100,000 units of their own currency and saving 500 a month. They are not exchange-rate conversions of one person’s money. Each uses the corresponding currency inputs and inflation reference. The same percentage allocation can have different forecast growth and risk.

*Today’s money, local currency units. †Difference in constant nominal monthly saving to reach a 300,000 target in today’s money. Compare the two scenarios within a row, not raw money amounts between countries.

What the example establishes and what it leaves out

The lower return is a deliberately chosen sensitivity. It is not a second institution’s forecast, a confidence bound or a prediction of losses. Smooth compounding isolates one assumption; real markets do not follow these lines. Sequence risk, tax, behavioural changes and future changes to inflation are outside this calculation. A target met on a steady path is not a probability of success.

Reproduce it

1. Open the assumption check. Keep the 60/30/10 allocation and ten-year horizon.
2. Enter 100,000 starting capital, 500 monthly saving, a 300,000 real target, a 0.3% annual fee and a −2 percentage point alternative.
3. Choose a currency, review its inflation setting and compare. Download the inputs and results or save a device snapshot.
4. Change one variable. Discuss what changed and what the calculation cannot tell you.

Reference returns come from the bundled 2026 J.P. Morgan currency editions, imported 2026-09-02. Portfolio risk uses Portfolio Lab’s shared covariance inputs; asset arithmetic returns are combined and converted to a portfolio compound-growth approximation. The sensitivity then changes that portfolio growth rate. An annual fee is deducted multiplicatively. Contributions occur at month end, using the effective monthly rate. Final values are deflated once.

Published forecasts have a 10 to 15 year horizon. They are dated planning references, not current market prices. Comparing other forecasting houses also requires matching asset definitions, dates, horizons, currency and real/nominal conventions; a large numerical spread alone is not proof of a useful investment opportunity.

• J.P. Morgan USD source workbook
• J.P. Morgan CAD source workbook
• J.P. Morgan GBP source workbook
• J.P. Morgan EUR source workbook
• J.P. Morgan ZAR source workbook

Illustrative analysis, not personal investment advice. Capital at risk.