See exactly how your money grows over time. Adjust your initial investment, monthly contributions, and interest rate to model any scenario — then export a full report as a PDF.
| Year | Balance | Total invested | Interest this yr | Total interest |
|---|
Lost wealth if you wait to start
How it works
Compound interest means you earn returns not just on what you invest, but on the interest you've already earned. Over time, this snowball effect becomes the most powerful force in wealth building — small amounts invested consistently can grow into life-changing sums.
The more frequently interest compounds, the faster your money grows. Daily compounding yields slightly more than annual compounding at the same rate, because each smaller interest payment starts earning its own returns sooner. For long time horizons, the difference adds up.
Time is your most valuable investment asset. Delaying by even one year means missing compounding on every dollar you would have earned in that period — and that gap widens every year after. The "Cost of Delay" panel in the calculator shows exactly what waiting costs you in your scenario.
Common questions
Use the preset buttons as a starting point. The S&P 500 has averaged roughly 10% annually over the long term before inflation. A balanced portfolio of stocks and bonds typically returns 6–7%. High-yield savings accounts currently sit around 4–5% depending on your country and bank.
Yes, if you want to understand what your future balance is worth in today's money. The 2.5% inflation toggle reduces your effective rate by 2.5%, giving you a "real return" figure. It's a more honest picture of purchasing power, especially for horizons of 20 years or more.
It reduces your annual return by your marginal tax rate, simulating returns in a taxable account. If your investments are in a tax-sheltered account — such as an ISA, Roth IRA, TFSA, or similar — leave this toggle off, since those gains are not subject to annual tax.
Yes — click the Export PDF button at the top of the year-by-year breakdown table. The report includes your full settings, summary metrics, cost of delay figures, financial milestones, and a complete year-by-year table formatted for print or sharing.
Simple interest is calculated only on your original principal. Compound interest is calculated on your principal plus all previously earned interest. Over time this difference becomes dramatic — a $10,000 investment at 7% simple interest earns $700 per year forever, while at 7% compound interest it earns more every single year as the balance grows.
Even small amounts make a meaningful difference when invested consistently over long periods. A general rule of thumb is to aim for saving 10–20% of your income, but starting with whatever you can afford is far better than waiting until you can invest more. Use the Monthly Contribution slider to model different amounts and see the long-term impact.
It shows exactly how much total wealth you would lose by waiting 1, 3, or 5 years before starting to invest, based on your current settings. The figures update in real time as you adjust your inputs — and they are often surprisingly large, even for short delays, because of the compounding you miss in those early years.
These are automatically calculated markers that show the year you are projected to reach key balances ($50k, $100k, $250k, $500k, $1M), the year your monthly interest income will cover your monthly contributions, and the year your total balance doubles what you have personally invested. They update instantly as you adjust your inputs.
It is a useful starting point for modelling long-term investment growth, but retirement planning involves additional factors — such as changing contribution rates over time, drawdown phases, government benefits, pension income, and tax treatment in retirement. For comprehensive retirement planning, consider speaking with a qualified financial adviser.
The calculator uses standard compound interest formulas and is mathematically precise based on the inputs you provide. However, real-world investment returns vary year to year — no investment grows at a perfectly steady rate. The results are projections based on a constant assumed rate, not guarantees of future performance.
Enter the amount you plan to invest today using the Initial Investment slider. This is your starting principal — the foundation everything else compounds on top of.
Use the Monthly Contribution slider to set how much you plan to add each month. Regular contributions dramatically accelerate growth — even modest amounts add up significantly over time.
Use the preset buttons — S&P 500 (10%), Balanced Portfolio (7%), or High-Yield Savings (4%) — or drag the slider to enter a custom rate that matches your investment type.
Drag the Years slider to match how long you plan to keep your money invested. The longer the horizon, the more dramatic the compounding effect becomes.
Toggle inflation adjustment to see results in today's purchasing power. Toggle after-tax returns and enter your tax rate to model a taxable investment account more accurately.
Review your summary metrics, milestones, cost of delay figures, and the year-by-year breakdown table. When you're ready, click Export PDF to save a full formatted report.
Compound interest is one of the most powerful concepts in personal finance, yet it is frequently underestimated. At its core, compounding means that your returns generate their own returns. Each period — whether daily, monthly, or annually — the interest you have already earned is added to your balance, and that larger balance then earns interest in the next period.
The result is exponential growth. In the early years of an investment, the effect feels modest. But as the years accumulate, the growth accelerates dramatically. A $10,000 investment at 7% per year grows to roughly $19,700 after 10 years — nearly double. After 20 years it becomes approximately $38,700. After 30 years it reaches around $76,100. The same money, the same rate, but the power of time transforms the outcome entirely.
This is why financial advisers so consistently emphasize starting early. The difference between beginning at age 25 versus age 35 is not simply 10 years of contributions — it is a decade of compounding on every dollar already invested, a gap that grows wider with every passing year.
A quick mental shortcut: divide 72 by your annual interest rate to estimate how many years it takes for your money to double. At 7%, your money doubles roughly every 10.3 years. At 10%, every 7.2 years. At 4%, every 18 years. Use the calculator above to model your exact scenario.
While a lump-sum initial investment is a powerful starting point, regular monthly contributions can be even more impactful over a long time horizon. Adding $500 per month to a $10,000 initial investment at 7% over 20 years results in a final balance of roughly $284,000 — compared to just $38,700 from the initial investment alone. The contributions themselves total $120,000 over that period, meaning compounding generated over $130,000 in additional wealth.
The frequency at which interest compounds also affects your final balance. Daily compounding produces slightly higher returns than monthly, which in turn beats annual compounding at the same nominal rate. For most long-term investment accounts, monthly compounding is the most common real-world frequency, though some savings accounts and bonds compound daily.