Start with what you have, add a bit monthly, give it time. See the year-by-year growth — and the moment the interest starts out-earning you.
Time beats rate. Ten extra years at a modest rate usually beats a slightly better rate over a shorter period. The earlier the start, the more of the final balance is growth rather than sacrifice.
The boring middle is normal. For the first several years the balance is mostly your own contributions and the growth looks like a rounding error. The table above exists to show the shape: flat-ish, then curved, then steep. Most people quit in the flat part.
The contribution is the controllable input. You can't control markets or rates; you can control the monthly amount. Even small increases compound dramatically — try re-running with 10% more. Where does the extra come from? Usually from spending that wasn't deliberate: run the subscription cost calculator or set up a zero-based budget and redirect what you find.
A note on honesty, since it's our thing: the smooth curve in any compound interest calculator is a mathematical illustration. Real investment returns arrive lumpy — up years, down years — and cash rates change. Use this to understand the mechanism and set contribution habits, not to predict a number.
Interest is calculated not just on your original money but on the interest it has already earned. Early on the effect looks unimpressive; over decades it dominates — which is why the year-by-year table above typically shows interest overtaking your own contributions somewhere in the second decade.
The annual rate is divided by 12 and applied every month, and your monthly contribution is added at the end of each month. Different accounts compound at different frequencies; monthly is a common and slightly conservative assumption for illustrations.
For cash savings, use your account APY. For long-term investing illustrations, people commonly test 4–7% to stay conservative relative to historical stock-market averages. No rate is guaranteed — this calculator is an illustration, not advice or a prediction.
No — the results are in nominal terms. A rough way to think in today’s money: subtract expected inflation from your growth rate (e.g. 6% growth minus 2.5% inflation ≈ 3.5% real) and run the calculator with that.