How Compound Interest Changes Over Time

Compound growth means returns can earn additional returns in later periods.

Early in a projection, contributions often dominate. Later, accumulated returns can become a larger share of growth.

A higher assumed return rate increases the projection, but it also increases the risk of overconfidence if treated as guaranteed.

Starting earlier gives each contribution more time to compound, which can be more powerful than increasing contributions later.

A future dollar amount is not the same as today's purchasing power.

Use inflation-adjusted value when comparing long-term scenarios, especially retirement or education planning.

A recurring fee reduces the balance available to earn future returns, so its long-term effect can be larger than the first year's charge. Taxes can also change when and how much of a return remains invested.

Model a gross-return scenario and a lower net-return scenario rather than subtracting one fee only at the end. The gap illustrates the cumulative effect without pretending to predict an actual portfolio.

Real returns vary from year to year, and a smooth calculator line is a simplified projection. Compare conservative, central, and optimistic assumptions while keeping contributions and time horizon constant.

If a decision only works under the optimistic case, the plan is sensitive to assumptions. Record the inputs and revisit them when fees, goals, or time horizon change.