Calculate how your money grows over time with compound interest. Compare daily, monthly, quarterly, and annual compounding frequencies.
Compound interest earns interest on both principal and accumulated interest. Formula: A = P(1 + r/n)^(nt). Example: $10,000 at 7% annually for 10 years grows to $19,672. The more frequent the compounding, the higher the returns.
Try an example:
Final Balance
$54,714
Total Interest
$20,714
Total Contributions
$34,000
Effective Annual Rate
7.23%
Growth Multiple
5.47x
Breakdown
Formula Used
A = P(1 + r/n)^(nt) + PMT * ((1 + r/n)^(nt) - 1) / (r/n)Where P = $10,000, r = 7%, n = monthly, t = 10 years
| Year | Interest | Balance |
|---|---|---|
| 1 | +$801 | $13,201 |
| 2 | +$1,033 | $16,634 |
| 3 | +$1,281 | $20,315 |
| 4 | +$1,547 | $24,262 |
| 5 | +$1,832 | $28,495 |
| 6 | +$2,138 | $33,033 |
| 7 | +$2,466 | $37,900 |
| 8 | +$2,818 | $43,118 |
| 9 | +$3,196 | $48,714 |
| 10 | +$3,600 | $54,714 |
Compound interest is interest calculated on both the initial principal and previously accumulated interest. At 7% compounded annually, $10,000 grows to $19,672 in 10 years and $76,123 in 30 years. The S&P 500 has delivered approximately 10% average annual returns since inception, meaning a lump-sum investment doubles roughly every 7.2 years through compounding. Time is the most powerful variable in the formula A = P(1 + r/n)^(nt).
Compound interest is often called the "eighth wonder of the world" - a quote attributed to Einstein. Unlike simple interest, which only applies to the original principal, compound interest calculates interest on both the principal and accumulated interest. The U.S. Securities and Exchange Commission (SEC) defines compound interest as "interest on interest" - the mechanism that makes invested money grow exponentially rather than linearly over time.
The power of compounding becomes dramatic over long time horizons. $10,000 invested at 7% for 10 years grows to $19,672 - but over 30 years it becomes $76,123. The same investment over 40 years reaches $149,745. According to Fidelity, the S&P 500 has returned approximately 10% annually since inception, with the most recent 10-year period (2016-2025) delivering around 13-15% annualized returns including dividends - demonstrating how compounding drives wealth over time.
For investors and business owners, understanding compound growth is essential for evaluating investments, comparing savings accounts, and planning for retirement. Combine this knowledge with ROI calculations to assess which investments deliver the best returns, or use our DCF Calculator to discount future cash flows back to present value - the mathematical inverse of compounding forward.
More frequent compounding produces higher returns because interest begins earning interest sooner. At 7% on $10,000 over 10 years: annual compounding yields $19,672, monthly yields $20,097, and daily yields $20,138. The formula is A = P(1 + r/n)^(nt), where n is the number of compounding periods per year. Moving from annual to monthly compounding captures most of the benefit; daily adds only marginally more.
A = P(1 + r/n)^(nt)
With regular contributions:
A = P(1 + r/n)^(nt) + PMT x ((1 + r/n)^(nt) - 1) / (r/n)
Your initial investment or deposit amount. This is the foundation on which all interest is calculated.
The nominal annual rate expressed as a decimal. 7% becomes 0.07 in calculations.
How often interest is calculated and added: daily (365), monthly (12), quarterly (4), or annually (1).
The total investment period. Longer time dramatically increases final results due to exponential growth.
Quick estimate for doubling time: divide 72 by your interest rate. At 7% interest: 72 / 7 = 10.3 years to double. At 12%: 72 / 12 = 6 years. This rule works best for rates between 6-10%. For income from investments you plan to grow, also track dividend yield alongside compounding to understand total return.
At 7% compounded monthly, $10,000 grows to $20,097 in 10 years, $40,388 in 20 years, and $81,165 in 30 years. Adding $200 monthly contributions transforms the outcome: after 30 years you reach $316,600, of which $244,600 is pure interest. The S&P 500 historical average of roughly 10% annually would turn $10,000 into $67,275 in 20 years with no additional contributions.
A 25-year-old starts investing $500/month in a retirement account earning 7% annually.
Over 80% of the final balance comes from compound interest, not contributions. Starting 10 years later would result in only $567,000 - less than half.
An emergency fund of $20,000 in a high-yield savings account. As of July 2026, top HYSA rates reach 4.10-4.50% APY (vs. the FDIC national average of 0.38%).
Your emergency fund grows over 23% while remaining fully liquid and FDIC-insured. At the national average rate of 0.38%, you would earn only $382 in the same period - a difference of $4,298 in lost interest.
Lump sum investment of $50,000 in an S&P 500 index fund with historical 10% average return.
The investment grows nearly 7x over 20 years. Note that stock market returns vary; this example uses long-term historical averages and doesn't account for fees or taxes. To measure the exact annualized rate across different holding periods, use a return on investment calculator.
For more guidance, visit the Planning tools hub and the Valuefy blog.
Use this alongside the NPV Calculator to discount future values back to the present, or the IRR Calculator to find the actual rate of return on uneven cash flows. For business planning, pair with the DCF Calculator and the WACC Calculator to model how compounding affects enterprise value over time.
Time is the most powerful variable - starting 10 years earlier can more than double your final balance due to exponential growth.
More frequent compounding (daily vs. annually) yields higher returns, but the difference is more significant at higher interest rates.
Regular contributions combined with compounding create powerful wealth-building momentum - even small monthly amounts grow substantially over time. For income-generating assets, combine this with dividend yield analysis to model total returns from both growth and income.
APY (Annual Percentage Yield) reflects true returns including compounding; always compare investments using APY rather than stated APR.
Use the Rule of 72 (72 / interest rate = years to double) for quick mental calculations of investment growth potential.