The most important chart in personal finance.
Time, contributions, and a steady return. Move the inputs and watch how the interest curve eventually dwarfs your principal — that crossover point is where wealth gets built.
Built and reviewed by Stephen Omukoko Okoth
Mathematical Economist · ex-Morgan Stanley FI · Equilar
Inputs
The three inputs that matter
Verdict
$ 691.1K after 30 years.
$ 501.1K of that is pure interest.
You contributed $ 190.0K of your own money. The rest came from sitting still.
Result
Decomposition
Final balance
$ 691.1K
You contributed
$ 190.0K
Interest earned
$ 501.1K
Common questions
What is compound interest?
Interest you earn on both the original principal and the accumulated interest from previous periods. The earlier you start, the more time compounding has to work — that's the whole game.
How does compounding frequency affect the result?
More frequent compounding (monthly vs. annually) marginally increases the effective yield. The bigger lever is duration: 30 years at 7% beats 20 years at 10% in most cases.
What's a realistic return?
For a globally diversified equity portfolio, ~7% real (after inflation) is the long-run number. Bonds add stability but reduce expected return. Cash loses to inflation.
Is the result before or after tax?
Before tax. If your investments are in tax-advantaged accounts (NSSF II, ISA, 401k, RA), the result is close to after-tax. In a taxable account, haircut by your marginal rate on dividends/gains.