Compound Interest Calculator
Estimate how your investments can grow with regular monthly contributions and compounding returns.
Your Investment
Adjust the values to see your wealth grow.
The amount you're starting with today.
The amount you'll add to your investment every month.
The average yearly growth you expect (stocks ~7%, bonds ~3%).
How long you'll keep the money invested.
End of period assumes contributions are made after interest is applied each month. Beginning of period assumes contributions are made before interest, resulting in slightly higher growth.
Assumes monthly compounding at 7% annual rate
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Over 20 years, $130,000 of contributions grows into $300,851 — about 57% of that comes purely from compound growth, not your own pocket.
Result Summary
This means you'll earn $170,851 in compound interest over 20 years — growing $130,000 of contributions into $300,851.
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How this calculator works
The compound interest calculator takes four simple inputs — your starting amount, an optional monthly contribution, an expected annual return, and how many years you'll let it grow — and projects how your balance changes year by year.
The output shows your final balance, how much you contributed, and how much came from growth alone (interest earning interest). The chart makes it easy to see when compounding really takes off.
Example calculation
Say you start with $5,000, add $300/month, expect a 7% annual return, and let it run for 20 years.
- Total contributions: $5,000 + ($300 × 12 × 20) = $77,000
- Final balance: roughly $176,000
- Of that, about $99,000 is pure growth from compounding.
What this means
More than half of the final balance comes from growth, not your own money. That's the headline lesson of compounding: the longer you stay invested, the more the returns themselves start doing the heavy lifting.
Tips
- Start now, even small. Time matters more than amount.
- Automate contributions on payday so you never "forget" to invest.
- Be conservative with the rate. 5–7% is a sensible long-term assumption.
- Don't interrupt the compounding. Avoid pulling money out early.
- Reinvest dividends rather than spending them.
Frequently asked questions
What's a realistic annual return to use?
For long-term diversified portfolios, 5–7% after inflation is a common assumption. Cash and high-yield savings accounts are closer to 0–4%.
Does the calculator account for inflation?
It projects nominal future values. To see today's purchasing power, use a slightly lower return rate (e.g. 5% instead of 7%).
Monthly or annual contributions — which is better?
Monthly is usually better because it benefits from more compounding periods and matches how most people get paid.
What if I can't contribute every month?
Even with gaps, the principle holds — any consistent contribution beats waiting. Start with what you can.
Keep exploring
Disclaimer: Estimates only — not financial advice. See how our calculators work for the formulas and assumptions used.