One lump sum, four rates
Put $10,000 away once, add nothing, and let it compound once a year for 30 years. The formula is FV = 10,000 × (1 + r)^30. Turn the rate dial and the endings spread out fast: $32,433.98 at 4%, $76,122.55 at 7%, $174,494.02 at 10% and $299,599.22 at 12%.
Why the gaps grow
The rate is in the exponent, so small differences in the rate turn into big differences in the result. 12% is three times 4%, but the ending is about 9.24 times as large. Going from 7% to 10% is just three points, yet the ending is about 2.29 times as large. Each extra point of return compounds on everything earned before it.
Reading the chart
All four lines start at $10,000 and stay close for the first few years. The spread opens up later, which is the same pattern as the doubling clock: at 12% money doubles about every 6 years, at 4% about every 18.
All four rates are hypothetical
None of these rates is a forecast or a promise. Real returns jump around from year to year and can be negative, and higher expected returns usually come with bigger swings. The page also leaves out fees, taxes and inflation; a 1% yearly fee alone would cut the 12% ending noticeably (see the fee calculator).
Sources
Last reviewed: Oct 9, 2026