Compound Interest Calculator

What this calculator does

This calculator computes the future value of an investment earning compound interest. It supports six compounding frequencies — from annual to continuous — and returns the final amount, total interest earned, and a growth factor showing how many times larger the investment becomes. Compound interest is interest earned on both the original principal and all previously accumulated interest.

Formulas

• A — final amount
• P — principal (starting amount)
• r — annual interest rate as a decimal (rate ÷ 100)
• n — compounding periods per year (1, 2, 4, 12, or 365)
• t — time in years
• e — Euler's number (≈ 2.71828)

How to use it

1. Enter the principal — your initial deposit or investment amount.
2. Enter the annual interest rate as a percentage (e.g. 7 for 7%).
3. Select the compounding frequency that matches your account or investment.
4. Enter the time in years over which the investment compounds.
5. Click Calculate to see the final amount, total interest, and growth factor.

Example

A $1,000 investment at 10% annual rate, compounded monthly, over 1 year:

• Monthly rate: 10% ÷ 12 = 0.8333%
• Formula: 1000 × (1 + 0.1/12)^12
• Final amount: $1,104.71
• Total interest: $104.71
• Growth factor: 1.1047×

Compare to annual compounding: $1,000 × (1.10)^1 = $1,100.00 — monthly compounding adds an extra $4.71 in the same year.

What the result means

The final amount is what your investment is worth after the specified time. The total interest is the gain beyond your original principal — the actual return generated. The growth factorshows how many times larger the investment became: a factor of 2.0× means the investment doubled. Higher compounding frequency and longer time periods both increase the final amount and growth factor.

Assumptions and limitations

• This calculator assumes a fixed interest rate for the entire period. Variable-rate investments will differ.
• No additional contributions are modeled. This calculates growth on the initial principal only.
• Daily compounding uses 365 periods per year. Some institutions use 360 (banker's year).
• Taxes on interest income are not accounted for.
• Results are for illustrative purposes only and do not constitute financial advice.