Compound Interest Calculator

Compound interest calculator: see how savings or investments grow with monthly, quarterly or daily compounding over time.

Editorial review: Farrow (pseudonym; identity and professional credentials are not disclosed). This page is for educational purposes, not professional advice.

Your inputs

Results update as you type. Nothing you enter leaves your device.

Future value

$15,669.93

Interest earned: $5,669.93
Effective APY: 4.594%

Example with the starting values

These results use the calculator's initial inputs. Change the values above to calculate your own estimate.

Inputs

Starting amount: 10000 $
Annual rate: 4.5 %
Years: 10
Compounds per year: 12

Results

Future value: $15,669.93
Interest earned: $5,669.93
Effective APY: 4.594%

How does the Compound Interest Calculator work?

Compound interest is interest earned on both the original deposit and the interest already added to it. The future value is A = P(1 + r/k)^(k·t), with principal P, annual rate r, k compounding periods per year and t years.

Use 12 for monthly compounding (most US savings accounts), 4 for quarterly, or 365 for daily. The effective APY is (1 + r/k)^k − 1, the true yearly growth after compounding.

For example, $10,000 at 4.5% compounded monthly for 10 years grows to about $15,670. The original $10,000 is the principal and about $5,670 is interest; this calculation assumes the rate remains unchanged and there are no additional deposits, withdrawals, taxes or fees.

The compounding frequency changes how often interest is added to the balance. With the same nominal 4.5% rate, monthly compounding produces an effective annual yield of about 4.59%; daily compounding is slightly higher. The difference is usually modest compared with changing the rate or leaving the money invested longer.

This calculator uses a fixed rate for the entire period. Bank savings rates can change, and investment returns are not guaranteed. The result is a future-dollar estimate, not an inflation-adjusted amount or a promise of earnings.

This tool does not include recurring contributions. To model deposits made each month, use a savings or retirement calculator that accepts contribution inputs; adding deposits to this compound-interest result would overstate what the displayed formula represents.

For monthly compounding at 4.5%, each period uses 4.5% divided by 12, or 0.375%, and ten years contains 120 periods. The balance earns interest on each new period's opening balance. That is why the result exceeds simple interest on the original $10,000, which would add $4,500 over ten years at the same nominal rate.

The entered annual rate is treated as a nominal rate, and the compounding frequency determines the effective APY. A bank may advertise APY directly, so compare like with like when checking an account offer. This estimate does not include income taxes on taxable interest, account fees, or the effect of inflation on purchasing power.

Sources

Investor.gov: Compound interest

Frequently asked questions

What is the formula for compound interest?

Compound interest uses A = P(1 + r/k)^(k·t). For $10,000 at 4.5% compounded monthly for 10 years, A = 10,000 × (1 + 0.045/12)^120, or about $15,670.

How long does it take money to double?

Use the Rule of 72: divide 72 by the annual rate. At 6% interest, money doubles in about 72 / 6 = 12 years. The exact answer with yearly compounding is 11.9 years.