Watch your savings grow. Use our free compound interest calculator to determine the future value of your investments over time.
| Breakdown | Total |
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| Initial deposit | $0.00 |
| Total contributions | $0.00 |
| Total interest earned | $0.00 |
| Estimated APY | 0.00% |
| Future value (ending balance) | $0.00 |
| Period | Contribution | Interest | Balance |
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| Enter values to see the schedule. | |||
Albert Einstein reportedly called compound interest "the eighth wonder of the world." Whether or not he actually said that, the math backs it up: money compounding at even a modest rate over decades grows into sums that seem almost impossible until you run the numbers yourself. This free compound interest calculator shows you exactly how your savings, investments, or retirement accounts grow — factoring in your starting balance, regular contributions, interest rate, compounding frequency, and time horizon. It works for savings accounts, CDs, Roth IRAs, 401(k)s, index funds, and any interest-bearing account.
Compound interest means you earn interest not just on your original principal, but on every dollar of interest you've previously earned. It's interest on interest — and over long periods, the growth it produces is exponential rather than linear. Simple interest, by contrast, only ever pays on the original principal and grows in a straight line. The difference between these two over 30 years is staggering, which is why understanding compounding is arguably the most important financial concept for anyone building long-term wealth.
The standard compound interest formula is:
A = P × (1 + r/n)^(nt)
Where: A = final amount | P = principal (starting balance) | r = annual interest rate (as a decimal) | n = number of times interest compounds per year | t = time in years.
For accounts with regular contributions (like a monthly savings deposit or 401k contribution), the formula extends to:
A = P(1 + r/n)^(nt) + PMT × [((1 + r/n)^(nt) − 1) ÷ (r/n)]
Where PMT = regular payment amount. This is what our Compound Interest Calculator uses — giving you the full picture including contributions, not just a lump sum projection.
The more frequently interest compounds, the faster your money grows — though the differences between daily and monthly compounding are smaller than most people expect. Here's what $10,000 at 5% annual interest grows to over 20 years:
Annual compounding: $26,533 | Monthly compounding: $27,126 | Daily compounding: $27,183
The difference between monthly and daily compounding on $10,000 over 20 years is only $57 — not the dramatic difference people often assume. What matters far more is the rate and the time. High-yield savings accounts (HYSA) typically compound daily, while most CDs compound monthly or quarterly. For long-term investments like index funds, compounding happens through reinvested dividends and price appreciation, which behaves similarly to annual compounding in practice.
No factor in compound interest is more powerful than time. Here's a comparison that illustrates this more clearly than any explanation:
Investor A invests $5,000/year from age 25 to 35 (10 years only, then stops) at 8% annual return. Total invested: $50,000.
Investor B invests $5,000/year from age 35 to 65 (30 years) at 8% annual return. Total invested: $150,000.
By age 65: Investor A has approximately $602,000. Investor B has approximately $566,000. Investor A invested for just 10 years — one-third as long — yet ends up with more money. The 10-year head start more than compensates for three times the contribution amount. This is the defining lesson of compound interest: start as early as possible, even if you can only contribute small amounts.
A Roth IRA is one of the best vehicles in the US tax code for compound growth, because your money grows tax-free and qualified withdrawals in retirement are completely tax-free. The 2026 contribution limit is $7,000/year ($8,000 if you're 50 or older). If a 25-year-old contributes $7,000/year to a Roth IRA invested in a broad index fund averaging 8% annual return for 40 years, they'd accumulate approximately $1,956,000 — all tax-free in retirement. The IRS has detailed rules on Roth IRA income limits and eligibility at IRS.gov. Use our Roth IRA Calculator for personalised projections.
High-yield savings accounts (HYSAs) have become significantly more attractive since the Federal Reserve raised interest rates. In 2026, top HYSAs offer APYs of 4%–5%, compared to the national average savings account rate of under 0.5%. On $20,000 at 4.5% compounding daily for 3 years, a HYSA produces approximately $2,900 in interest — versus $300 from a standard 0.5% savings account. The FDIC insures deposits up to $250,000 per depositor per institution — check coverage at FDIC.gov. Use our Savings Calculator to model HYSA growth.
Dave Ramsey's widely cited investment guidance is built on compound interest principles — specifically, the power of consistently investing 15% of gross income into tax-advantaged accounts (401k, Roth IRA) over a 20–30 year career. His illustrative examples often use a 10%–12% assumed annual return (the historical S&P 500 long-term average before inflation). While financial planners often suggest using a more conservative 6%–8% for planning purposes, the compound interest math at any rate demonstrates the same core message: consistency and time matter more than trying to time the market. Use our Investment Calculator to model any assumed return rate.
$25,000 at 6% annual rate for 25 years:
Simple interest: earns $37,500 in interest ($1,500/year × 25), final balance $62,500
Compound interest (annual): final balance approximately $107,297 — earning $69,797 in interest
Compound interest (monthly): final balance approximately $111,219 — earning $73,719 in interest
Compound interest produces nearly double the final balance of simple interest over 25 years on the same principal at the same rate. This is not magic — it's math. And it works in reverse too, which is why high-interest debt (credit cards compounding at 20%+) destroys wealth just as surely as compounding savings builds it. See our Credit Card Payoff Calculator to see compound interest working against you in debt.
The time value of money is the financial principle that a dollar today is worth more than a dollar in the future — because today's dollar can be invested and grow. This concept underpins mortgages, retirement planning, bond valuation, and investment analysis. Our Future Value Calculator and Present Value Calculator let you explore both directions of this concept — projecting what money today will be worth tomorrow, and discounting what future money is worth in today's terms.
Enter your starting principal (initial deposit or current balance). Add your regular contribution amount and frequency (monthly, quarterly, or annually). Enter your expected annual interest rate or return rate. Choose your compounding frequency. Set the time period in years. Click Calculate. You'll see your final balance, total interest earned, total contributions, and a year-by-year growth table showing how your money builds over time.
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The Rule of 72 is a quick mental math shortcut: divide 72 by your annual interest rate to find approximately how many years it takes your money to double. At 6% return, 72 ÷ 6 = 12 years to double. At 8%, it doubles in 9 years. At 10%, in 7.2 years. It's not perfectly precise but is accurate enough for quick planning and helps make the power of higher returns viscerally clear.
At 7% annual return (a conservative stock market estimate after inflation): 10 years → $19,672 | 20 years → $38,697 | 30 years → $76,123. At 10% (historical S&P 500 nominal average): 10 years → $25,937 | 20 years → $67,275 | 30 years → $174,494. The difference between 7% and 10% over 30 years is over $98,000 on a single $10,000 deposit — illustrating why investment fees and return rates matter so much over long time horizons.
Yes — and this is critically important. Credit card interest typically compounds daily at rates of 20%–30% APR. A $5,000 credit card balance at 22% APR paying only minimum payments can take 15+ years to pay off and cost over $7,000 in interest — more than the original balance. The same mathematical force that builds wealth in investments destroys it in high-interest debt. Paying off high-interest debt before investing (except to capture employer 401k matching) is almost always the mathematically correct choice.
Disclaimer: Compound interest projections are estimates based on consistent returns, which are not guaranteed for investments. Stock market returns fluctuate significantly year to year. Past performance does not guarantee future results. This calculator is for educational and planning purposes only and does not constitute investment or financial advice. Consult a qualified financial advisor before making investment decisions. For regulatory information on investment accounts, visit SEC.gov/investor.
The compound interest formula is A = P × (1 + r/n)^(nt). A is the final amount, P is principal, r is annual rate (as decimal), n is the number of compounding periods per year, and t is the number of years. For $10,000 at 7% compounded monthly for 20 years: A = 10000 × (1 + 0.07/12)^(12×20) = $40,387. Daily compounding gives $40,535; annual compounding gives $38,697.
The more often interest compounds, the faster money grows — but the difference between daily and monthly compounding is small. Over 30 years at 7%, $10,000 grows to $81,610 with daily compounding and $81,310 with monthly. Compounding frequency matters most at high interest rates (15%+ on credit card debt, for example), where monthly-vs-daily can cost hundreds per year.
Simple interest pays only on the original principal: $10,000 at 5% simple interest for 10 years = $15,000. Compound interest pays on interest earned: $10,000 at 5% compounded annually for 10 years = $16,289. Over 30 years, compounding makes the gap far larger — $43,219 vs $25,000. Every long-term investment account uses compound interest.
Adding monthly contributions transforms compound interest. $300/month at 8% for 35 years grows to $690,000 — and only $126,000 came from your contributions. The remaining $564,000 is compound growth. This is why starting early matters more than contributing more: time does the heavy lifting, not the amount.
To estimate how long it takes to double your money, divide 72 by the interest rate. At 8% return, money doubles every 9 years. At 10%, every 7.2 years. At 6%, every 12 years. The Rule of 72 is a useful mental shortcut for evaluating any investment opportunity without a calculator.
A = P × (1 + r/n)^(nt), where P is principal, r is annual rate, n is compounding periods per year, and t is years.
Only a little at typical savings rates. At 5% annual, daily vs yearly compounding produces about 2–3% more over 30 years.
Divide 72 by your annual return rate to estimate how many years it takes money to double. At 8%, money doubles every 9 years.
Yes — the terms are interchangeable. Compounding applies to savings accounts, bonds, and investment portfolios alike.
Massively. On a 35-year horizon, adding $300/month to a starting $10,000 at 8% turns $136,000 of contributions into $690,000 via compounding.