What are you saving?
£10,000 plus £250 a month becomes £148,612 after 20 years
This is arithmetic, not a forecast. It applies 6.0% a year, compounded monthly, to the amounts above. No forecasting house claims a market actually returns that figure every single year, only that it is what a run of years might average out to; the table below shows how much the cited rates disagree with each other.
You paid in £70,000; growth added £78,612. Growth alone passes everything you paid in during year 19.
Growth rates below are ten-year nominal US equity forecasts, quoted in US dollars by the houses that publish them and applied here as a plain percentage regardless of which currency you picked: this tool does not convert between currencies. The real-terms figure deflates at the rate above, defaulted to Office for National Statistics, Retail Prices Index long run series’s own record for GBP. See the full inflation calculator for the published history behind that default.
6.0% of what, exactly?
14 forecasting houses publish a ten-year US equity number and they do not agree, from Research Affiliates at 3.1% to BNY Mellon at 7.6%. The same plan under the consensus, the most cautious, and the most optimistic:
| House | 10-year forecast | This plan becomes |
|---|---|---|
| Consensus median (the default above) | 6.0% | £148,612 |
| Research Affiliates | 3.1% | £101,553 |
| BNY Mellon | 7.6% | £185,650 |
Nominal against real
The gap is what inflation takes.
What you paid in, and what it earned
Growth passes everything paid in during year 19: that is where the growth band becomes taller than the paid-in band.
The same plan, at every house’s assumption
14 lines, one per forecasting house. The spread is not noise; it is how much the answer depends on a number most calculators invite you to guess.