Results are estimates for guidance only and do not constitute financial advice. Always consult a qualified professional.
How to Use the Compound Interest Calculator
- Enter your initial principal — this is the starting amount you plan to invest or deposit.
- Set the annual interest rate — enter the yearly rate as a percentage. Try different rates to compare outcomes.
- Choose the compounding frequency — select how often interest is calculated and added to your balance: daily, monthly, quarterly, or annually.
- Enter the time period — specify how many years you plan to keep the money invested.
- Add monthly contributions (optional) — if you plan to add money each month, enter the amount here. Leave at 0 for a lump-sum calculation.
- Click "Calculate" — the calculator shows your final amount, total interest earned, and total contributions.
- View the year-by-year table — click the toggle to see how your balance grows each year.
How Compound Interest Works
Compound interest is calculated using the formula A = P(1 + r/n)^(nt), where P is the principal, r is the annual interest rate expressed as a decimal, n is the number of compounding periods per year, and t is the number of years. Unlike simple interest, which only applies to the original principal, compound interest is calculated on both the principal and all previously accumulated interest. This creates an exponential growth effect that becomes more powerful over longer time periods. When monthly contributions are added, each contribution also begins earning compound interest from the date it is deposited. The compounding frequency determines how often interest is calculated and added to the balance. Daily compounding produces slightly higher returns than monthly compounding, which in turn produces more than quarterly or annual compounding. However, the difference between daily and monthly compounding is relatively small for most practical purposes. The real power of compound interest comes from time and consistency, which is why starting early and making regular contributions is so effective for building wealth.
What is compound interest?
Compound interest is interest calculated on both the initial principal and the accumulated interest from previous periods. Unlike simple interest, which is only calculated on the principal, compound interest allows your money to grow exponentially over time. The longer your money compounds, the faster it grows.
How does compounding frequency affect returns?
The more frequently interest is compounded, the more total interest you earn. Daily compounding earns slightly more than monthly, which earns more than quarterly or annually. The difference becomes more significant with larger amounts and longer time periods, though the gap between daily and monthly compounding is usually small.
What is the compound interest formula?
The formula is A = P(1 + r/n)^(nt), where P is the principal amount, r is the annual interest rate as a decimal, n is the number of times interest compounds per year (12 for monthly, 365 for daily), and t is the number of years. The result A is the total amount including both principal and interest.
How do monthly contributions affect compound interest?
Regular monthly contributions dramatically increase your final amount because each contribution also earns compound interest from the moment it is deposited. Starting early with even small monthly contributions can result in significantly more wealth than a larger lump sum invested later, thanks to the additional compounding time.
What is the Rule of 72?
The Rule of 72 is a quick way to estimate how long it takes for an investment to double. Divide 72 by the annual interest rate to get the approximate number of years. For example, at 6% interest, your money doubles in roughly 12 years. At 8%, it doubles in about 9 years.
Is compound interest the same as APY?
APY (Annual Percentage Yield) already accounts for compounding frequency, so it reflects the true annual return. A 5% nominal rate compounded monthly has an APY of about 5.12%. When comparing savings accounts or investments, APY provides a more accurate comparison than the nominal interest rate alone.