Interest Calculator
Calculate simple and compound interest on your investments or loans.
Result
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What is this?
The Interest Calculator computes both simple and compound interest on any principal, rate, and time period, showing the final amount and the interest earned or owed. It covers savings accounts, fixed deposits, loans, and informal lending between friends where a fair rate needs proving.
Simple interest grows in a straight line: each year earns the same amount because it is charged only on the original principal. A 1,000 deposit at 5 percent for 3 years earns 150, no matter what. Compound interest grows exponentially because each period earns interest on the accumulated total as well; the same 1,000 at 5 percent compounded annually reaches about 1,157.63 after 3 years. The gap between the two widens dramatically over long horizons, which is why compounding is called the eighth wonder of investing.
For compound mode, choose the compounding frequency: annually, semi-annually, quarterly, or monthly. More frequent compounding raises the effective annual rate slightly - 5 percent nominal compounded monthly is about 5.12 percent effective. The tool reports that effective rate so you can compare offers quoted on different bases.
For the long-view projection of recurring deposits, pair this with the Interest Calculator. All arithmetic runs locally in your browser.
Simple interest grows in a straight line: each year earns the same amount because it is charged only on the original principal. A 1,000 deposit at 5 percent for 3 years earns 150, no matter what. Compound interest grows exponentially because each period earns interest on the accumulated total as well; the same 1,000 at 5 percent compounded annually reaches about 1,157.63 after 3 years. The gap between the two widens dramatically over long horizons, which is why compounding is called the eighth wonder of investing.
For compound mode, choose the compounding frequency: annually, semi-annually, quarterly, or monthly. More frequent compounding raises the effective annual rate slightly - 5 percent nominal compounded monthly is about 5.12 percent effective. The tool reports that effective rate so you can compare offers quoted on different bases.
For the long-view projection of recurring deposits, pair this with the Interest Calculator. All arithmetic runs locally in your browser.
Formula
Simple: Interest = P x r x t
Compound: Amount = P x (1 + r/n)^(n x t); Interest = Amount - P
n = compounding periods per year
Compound: Amount = P x (1 + r/n)^(n x t); Interest = Amount - P
n = compounding periods per year
Frequently Asked Questions
What is compound interest?
Interest calculated on both the initial principal and the accumulated interest from previous periods.