Project the growth of an investment, find out how long until you hit a goal, or work out the monthly amount you need. Compound interest does the heavy lifting. This shows you the numbers.
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Your first issue lands next week. In the meantime, scroll down for the year-by-year breakdown of your projection.
See how your contributions and compound growth stack up each year.
The reason a calculator like this surprises people is compounding. Your returns earn returns. In year one, you earn a return on what you put in. In year two, you earn a return on your contributions plus year one's gains. Repeat that for 30 years and the growth dwarfs the money you actually saved.
Time is the most powerful input in this calculator, more than your contribution and more than your return. Two investors each put in $300 a month at 7%. One starts at 25 and stops at 35, contributing for just 10 years. The other starts at 35 and contributes every month until 65, for 30 years. The early starter, who put in one-third as much money, often ends up with a larger balance at 65. The extra decades of compounding outweigh the extra contributions.
This is why the single most useful thing most investors can do is start now with whatever they can, rather than wait until they can invest a larger amount.
The return you plug in changes everything, so it is worth getting right. Here is a grounded set of numbers to work from:
| Portfolio type | Before inflation | After inflation |
|---|---|---|
| 100% U.S. stock index | ~10% | ~7% |
| 80% stocks / 20% bonds | ~8.5% | ~5.5% |
| 60% stocks / 40% bonds | ~7.5% | ~4.5% |
| Cash / savings | ~4% | ~1% |
Using the after-inflation column gives results in today's dollars, which is the honest way to plan: $1 million in 30 years will not buy what $1 million buys now. These are long-run averages, not promises. Any single year can swing 20% or more in either direction, and the order of those years matters near retirement.
Early on, almost all of your balance is money you contributed. The compounding piece looks small for the first decade. That is the part most people quit during. The curve bends upward later, when the growth on prior growth starts to outpace your monthly deposits. On a 30-year horizon, the back half is where the majority of the final balance is created, which is the entire argument for not touching it.
This calculator shows growth before fees. In the real world, the fund you buy charges an expense ratio, and that comes straight off your return. A fund returning 7% with a 0.75% expense ratio actually compounds at about 6.25% for you. On a long horizon that gap is worth tens of thousands of dollars. Run the same plan through the ETF fee calculator to see exactly how much a high-fee fund would cost you, then keep more of this growth by choosing low-cost index funds. Our expense ratios guide covers what counts as a reasonable fee.
It uses monthly compounding, the same cadence most funds and accounts use. Your starting amount and each monthly contribution grow at one-twelfth of the annual rate, every month, for the full horizon. Grow mode projects the ending balance. Goal mode solves for the number of years to reach your target. Save mode solves for the monthly contribution that lands you on your target by your chosen date. None of it accounts for taxes, which depend on your account type. For tax-advantaged growth, look into a Roth IRA or 401(k) alongside a taxable brokerage account.
Educational purposes only. This calculator illustrates the mathematics of compound growth based on the inputs you provide. It does not constitute financial advice, investment recommendations, or personalized guidance. Projections are hypothetical and assume a constant annual return, which real markets do not deliver. Results exclude fees and taxes. ETF BFF is not a registered investment advisor. Past performance does not guarantee future results. Always do your own research and consider consulting a qualified financial professional before making investment decisions.