Compound Interest & Investment Growth Calculator
See how a starting amount plus regular contributions could snowball over time — the single most important idea in investing. Drag any slider and watch the future value update live, in both future and today's dollars. Educational only; nothing here is advice.
How your money grows
Real markets don't move in a straight line — this is the smooth average. Expect a bumpy ride with down years along the way; the actual path could end up well above or below this line.
How compound interest actually works
Compound growth is simply earning returns on your returns. In year one you earn a return on what you put in. In year two you earn a return on your contributions and on last year's gains — and so on, each year working off a bigger base. Early on it looks almost linear; given enough time the curve bends sharply upward. That bend is the whole game, and it's why the most valuable ingredient is usually time, not a heroic rate of return.
The rule of 72
Want a quick gut-check without a calculator? Divide 72 by your annual return to estimate how many years it takes your money to double. At 7%, that's about 72 ÷ 7 ≈ 10 years to double; in 30 years it would double roughly three times — eight-fold — before you add a single new dollar.
Why fees and inflation matter
Two quiet forces work against you. Fees come straight off your return every year, so a 2% fee on a 7% return keeps only 5% — and over decades that gap compounds into a huge difference. Inflation erodes what your dollars buy, which is why the big future number can be misleading. Flip the toggle above to "today's dollars" to see the honest, purchasing-power version.
Contributions vs. return
In the early years, the size of your contributions matters most — that's the part you fully control. Later, your investment growth can dwarf what you add. The growth chart shows the moment the growth slice overtakes your contributions: that crossover is compounding taking over the heavy lifting.
Turn this into a retirement plan
Size how much to actually save for a specific Canadian retirement number — with a real, tax- and benefit-aware drawdown (CPP, OAS, RRIF), not a flat rule.
Where to invest →Compare one-ticket ETFs
This tool assumes a return — see how Canada's all-in-one index ETFs (XEQT, VEQT, VGRO…) actually compare on growth, drawdown and fees.
Common questions
What is compound interest?
Compound interest — or compound growth — is when the returns you earn start earning returns of their own. Reinvest your gains instead of spending them and the growth curve bends upward over time, because each year you're earning on a steadily bigger balance. The longer your time horizon, the more dramatic the effect, which is why starting early tends to matter more than starting big.
How much will $500 a month grow to?
It depends on your return and how long you stay invested. As an illustration, $500 a month for 25 years at a 7% average annual return grows to roughly $400,000 — of which about $150,000 is what you contributed and the rest is growth. Change the inputs above to model your own numbers. It's a hypothetical, not a guarantee.
What rate of return should I use?
Returns are never guaranteed, but a broadly diversified stock index has historically averaged high single digits per year before inflation over the long run — with any single year or decade far higher or lower. Important: this calculator treats the rate you enter as a nominal (before-inflation) return and shows the inflation-adjusted value separately, so don't subtract inflation yourself. Many people model a conservative 5–7% and watch how sensitive the answer is, rather than hunting for one 'correct' number.
Is a 7% return realistic?
Over long periods, globally diversified equities have delivered high-single-digit average annual returns before inflation — but with big swings along the way, including multi-year stretches of losses. Treat the number as a planning assumption to stress-test, not a promise, and remember it's before inflation (the tool adjusts for that separately). Drag the return slider down to see how much your result depends on it.
What's the difference between nominal and 'today's dollars'?
The nominal value is the raw future dollar figure. The real, or inflation-adjusted, value is what those dollars would actually buy in today's money once inflation has eroded them. A $1,000,000 balance 30 years from now might only have the purchasing power of around $500,000 today — so this calculator always shows both.
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How this is calculated
- Compounding: monthly. Your contribution is converted to a monthly-equivalent (so weekly/quarterly/yearly all map to the same per-month amount) and added at the start of each month, then grown. Depositing at the start of the month reads slightly higher than calculators that deposit at month-end.
- Return is "nominal" (before inflation). The rate you enter is treated as a before-inflation return. The "today's dollars" figure then discounts the result by your inflation rate, so it reflects real purchasing power — that's why it's lower than the headline number.
- Fees are subtracted straight from the return every year (a 2% fee on a 7% return compounds as 5%).
- Contributions are held flat in dollar terms unless you set a yearly increase under Advanced. A flat amount buys a little less each year as prices rise, which the "today's dollars" figure reflects — set "raise contributions" to about your inflation rate to keep pace.
- "Income at 4%" is shown in today's dollars — the 4%-rule first-year withdrawal from the real balance, before tax. It's an illustration of scale, not a test of whether the money lasts.
- The big number is one smooth path. Real markets don't deliver a constant return — they swing, including losing years — so the result is rounded and best read as a ballpark, not a forecast. Taxes are not included.