Compound interest calculator for a starting amount, annual rate, and time. Choose a compounding frequency and review the total amount and interest.
The Compound Interest Calculator projects the future value of a single starting amount using A = P(1 + r/n)^(nt). Set the compounding frequency n and enter the principal, annual rate, and time in years. Review the total amount and the interest above the starting principal.
This is a fixed-rate, lump-sum model. It does not account for regular deposits, withdrawals, loan repayments, fees, taxes, or changing rates. Treat the result as a calculation under your chosen assumptions, not a promised return or a complete loan quote.
Compound interest applies to the principal and interest accumulated in earlier periods. At 10% compounded annually, 1,000 earns 100 in year one, then 110 in year two on the new balance of 1,100, then 121 in year three. Simple interest on the original 1,000 at 10% would instead be 100 each year.
The formula A = P(1 + r/n)^(nt) uses principal P, annual rate r as a decimal, periods per year n, and time t in years. For example, 5% = 0.05 in the formula; the input field accepts 5.
The total is A, and interest is A − P. Each period multiplies the balance by (1 + r/n). Across nt periods, the multiplier is (1 + r/n)^(nt).
The frequency n can be annual (1), semi-annual (2), quarterly (4), monthly (12), or daily (365). With a fixed nominal annual rate, increasing frequency approaches the continuous-compounding expression P × e^(rt). Use the frequency in the product terms rather than choosing a higher one to improve the projection.
Example 1: 10-year savings. 10,000 at 6% per annum compounded monthly for 10 years. A = 10000 × (1 + 0.06/12)^(12×10) = 10000 × (1.005)^120 = 10000 × 1.8194 = 18,193.97. Interest earned: 8,193.97. Compare with simple interest at the same rate: 10000 × 6 × 10 / 100 = 6,000 of interest. Compound interest delivers 2,194 more; that's the "magic of compounding".
Example 2: 30-year retirement projection. 50,000 at 7% per annum compounded annually for 30 years. A = 50000 × (1.07)^30 = 50000 × 7.6123 = 380,613.16. Interest: 330,613.16. The principal more than 7×-es over three decades.
Example 3: Compounding frequency comparison. 1,000 at 10% per annum for 5 years. Annual compounding: 1,000 × (1.10)^5 = 1,610.51. Monthly: 1,000 × (1 + 0.10/12)^60 = 1,645.31. Daily: 1,000 × (1 + 0.10/365)^1825 = 1,648.39. The difference between monthly and daily is small (about 3); between annual and monthly noticeable (about 35). For most purposes, monthly compounding is a good approximation of higher frequencies.
The examples assume an unchanged rate, no money added or removed, and the stated compounding schedule. They illustrate arithmetic, not the likely performance of an investment. A mortgage or credit-card repayment schedule needs a model that includes its payments and contract rules.
Check whether a quoted rate is nominal or an effective yield before entering it. Do not apply compounding to an already effective annual yield as though it were a nominal rate.
The rule of 72 is only a rough doubling-time estimate: divide 72 by the annual percentage rate. At 6%, that suggests about 12 years; at 8%, about 9 years. Compare a projection using the actual rate and frequency rather than treating that shortcut as exact.
Inflation changes purchasing power, and simply subtracting it from the nominal rate is an approximation. Review real-return assumptions separately for long-term planning.
The arithmetic uses Math.pow. That implementation detail does not establish a privacy guarantee. Follow your organization's handling requirements before entering confidential financial information.
How to Use Compound Interest Calculator - Formula and Future Value
Enter the original principal in Principal Amount. This model uses a single starting sum, not ongoing deposits.
Enter Annual Interest Rate (%) and Time Period (years), then choose the compounding frequency stated in your example or agreement.
Read Total Amount and Interest Earned. Change inputs to compare scenarios, and check fees, taxes, rate changes, or repayments separately.
Compound interest calculator for a starting amount, annual rate, and time. Choose a compounding frequency and review the total amount and interest.
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