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.
The flat early years are when fear argues for quitting. A dated fear log shows, ninety days later, how often that forecast was right.
See what a panic sale actually interrupts before deciding anything in a scary market.
You enter a starting balance, monthly contribution, expected annual return and number of years. It applies the standard future-value formula, compounded monthly, and splits the result into what you contributed and what compounding added on top. The return is held constant, which is an assumption, not a fact.
Time, usually. Stretching the horizon from 20 to 30 years typically moves the ending number more than nudging the return assumption from 7% to 9%. The compounding window is the most expensive variable to shorten, and lost years are the only ones nobody can buy back.
Because compounding works on the balance, and early on the balance is mostly your own contributions. The curve looks nearly flat for about the first decade, then steepens. Almost everyone who quits, quits during that flat part. Years 8, 12 and 17 are where simply staying invested matters more than picking funds.
Not the way people fear. While you are contributing, rough years can actually help, because each contribution buys more shares at lower prices. This calculator assumes you are in that contribute phase. Once you start withdrawing, rough years hurt twice, and the Sequence of Returns calculator covers that side.
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.
Who I work with: founders, business owners and families who want one fee-only advisor for the whole picture. Ongoing planning runs $150 to $500 a month; investment management is about 1% a year, lower as assets grow; no account minimum. Not ready for that? The Purpose Pit Stop is a half day for $750.
Set your numbers and the napkin writes itself. Download it, share it, tape it to the fridge. Numbers argue better when they're drawn.
Chapter 7, “The Plan You’re Afraid to Trust”: the decision you make worst under pressure, and how to make it in advance. Ten minutes. Drop your email and I’ll send it, plus Field Notes once a month.
One per month. Unsubscribe with one click.