Start somewhere. Add a little every month. Give it time. That's the entire engine — and the part that does the heavy lifting takes 20 to 30 years to show up. This calculator shows what consistent contributions actually become.
Drop in a starting balance, your monthly contribution, an expected return, and a time horizon. The math is the standard future-value formula — compounded monthly. The bars show what you contributed versus what compounding gave you on top at five-ish-year intervals.
The honest disclaimer: a constant rate of return is an assumption, not a fact. Real markets are lumpy. But over 20+ year horizons, the average tends to dominate — which is why this is one of the calcs people who get this stuff right tend to look at often, and people who don't tend to never look at.
Hypothetical illustration only. Constant rate of return assumed. Past performance doesn't guarantee future results. For educational purposes — not investment advice.
Most people, the first time they see compounding visualized, do one of two things: they get excited about the ending number, or they get depressed about how slowly it starts. Both miss the actual lesson.
The lesson is the slope. The line is nearly flat for the first decade and steepens dramatically after that. Compounding is rear-loaded — and almost everyone who quits, quits during the flat part.
Three honest takeaways the calculator can't quite show:
Time matters more than rate. Pushing the horizon from 20 to 30 years usually moves the final number more than nudging the return assumption from 7% to 9%. The compounding window is the most expensive variable to shorten, and the only one nobody can buy back.
Constant return is fiction. Real markets deliver the same average through wildly different paths. If you're invested while contributing, the rough years actually help — you buy more shares cheaper. If you're invested while withdrawing, the rough years hurt twice. This calculator assumes you're in the contribute phase.
The boring middle is where the work happens. Year 8, year 12, year 17 — those are the years where staying invested is the only thing that matters. Not picking funds. Not rebalancing fancier. Just continuing.
If the numbers above are missing one variable that matters most — like "what should my contribution actually be" — that's worth a 30-minute call.