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Compound interest calculator

Estimate long-term investment growth from principal, contributions, return rate, and compounding frequency.

Model principal, recurring contributions, annual return, time horizon, compounding frequency, and an optional inflation-adjusted view.

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Result

Enter your values and tap Calculate growth.

How to use this calculator

Enter your starting balance, contribution amount and frequency, annual return rate, time horizon, and compounding frequency. Tick the checkbox to also see a purchasing-power estimate adjusted for 2.5% annual inflation.

Frequently asked questions

What is compound interest?

Compound interest means your earnings are reinvested so that future interest is calculated on both the original principal and all accumulated growth — not just the starting amount. Over long periods this creates exponential rather than linear growth.

How does compounding frequency affect the result?

More frequent compounding (daily vs annually) produces a slightly higher effective annual rate because interest is added to the balance more often. For typical market returns the difference between monthly and daily compounding is small, but it compounds meaningfully over decades.

What does contribution frequency mean?

Contribution frequency controls how often you add money. The calculator converts weekly, biweekly, monthly, or annual contributions into an equivalent monthly figure for the projection. A monthly contribution of $500 is equivalent to a weekly contribution of about $115.

What annual return rate should I use?

Use the real (inflation-adjusted) rate if you want purchasing-power terms, or the nominal rate if you want raw future dollars. Long-run global equity indexes have returned roughly 7–10% nominal and 5–7% real historically, but past returns do not guarantee future results.

Does my saved progress get sent to a server?

No. Your inputs live only in the URL of this page. When you bookmark the page, you save your data locally to your own device. Nothing is uploaded, stored on a server, or tracked.

Compound interest scenarios

Use this calculator to compare conservative, base, and aggressive growth assumptions side by side. Bookmark the page after entering values — your inputs are stored in the URL automatically.

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People also ask

How often should interest compound to maximize growth?

The more frequently interest compounds, the faster growth accelerates — daily compounding beats monthly, which beats annual. However, the practical difference between daily and monthly compounding is small for most savings rates. The compounding frequency matters far less than the rate and time horizon. A higher rate compounded annually beats a lower rate compounded daily.

What is the Rule of 72?

The Rule of 72 is a mental shortcut for estimating how long it takes to double an investment: divide 72 by the annual interest rate. At 6%, money doubles in roughly 12 years; at 9%, in about 8 years. It's an approximation, but it's accurate enough for planning conversations and quick sanity checks before running the full calculation.

Does compound interest work the same for debt?

Yes — and it works against you. Credit card balances compounding at 22% annually double in about 3.3 years with no payments. The same mathematics that build wealth in savings accounts accelerate debt when interest is charged on an unpaid balance. This is why high-rate debt elimination is often mathematically equivalent to a guaranteed high-return investment.

Real-world scenarios

Comparing a HYSA vs index fund over 10 years

Enter $10,000 at 4.5% (a competitive high-yield savings rate) compounded monthly for 10 years — you get roughly $15,670. Run the same $10,000 at a 7% real return (a conservative long-term index fund assumption) — you get roughly $19,670. The $4,000 gap illustrates the cost of keeping long-term money in savings instead of equities.

The impact of adding monthly contributions

Starting with $5,000 and adding $200/month at 7% for 20 years produces roughly $107,000. Starting with $5,000 and adding nothing produces only $19,350. The contributions matter more than the starting balance by a wide margin in medium time horizons — the calculator makes this comparison instant.

Modeling a CD ladder at different terms

Compare a 12-month CD at 5.0%, a 24-month at 4.6%, and a 60-month at 4.2% using the same principal. The shorter CD compounds less but gives you access to reinvest if rates rise. Run each term in the calculator to see total interest earned, then decide based on your liquidity needs and rate outlook.