Interest Calculator

How much interest will you earn — or pay? Enter the principal, the interest rate and the time, and this interest calculator works out simple interest and compound interest, with the future value.

Example filled in: $10,000 at 5% interest for 3 years, compounded monthly. 5% is an example rate, not a live market rate. Change any number below to run your own interest.

How to use this interest calculator

Enter the principal — the starting amount.
Enter the annual interest rate.
Enter the time in years.
Pick simple or compound interest. For compound interest, pick how often it compounds.
The interest calculator shows the future value and the interest earned.

Formula

Simple interest: I = P × r × t, where P is the principal, r is the annual rate and t is the time in years. Future value is P + I. Compound interest: A = P(1 + r/n)^nt, where n is how many times a year interest compounds. Interest earned is A − P. Compounding more often earns a little more, because interest starts earning interest sooner.

Worked example — $10,000 at 5% for 3 years

Simple interest on $10,000 at 5% (an example rate) for 3 years is $10,000 × 0.05 × 3 = $1,500.00 of interest, for a future value of $11,500.00. Compounded monthly, the same $10,000 grows to $11,614.72, with $1,614.72 of interest — $114.72 more than simple interest, because each month’s interest earns interest in the months after. Compounded once a year it grows to $11,576.25. Check it above — the interest calculator gives the same answers.

Frequently asked questions

What is the difference between simple and compound interest?

Simple interest is charged or paid only on the original principal. Compound interest is charged or paid on the principal plus the interest already added, so it grows faster. On $10,000 at 5% for 3 years, simple interest is $1,500.00 and compound interest (monthly) is $1,614.72.

How much interest will I earn on $10,000 at 5%?

Over 3 years, $1,500.00 with simple interest, or $1,614.72 with monthly compounding. Over 1 year it is $500.00 either way, because there is no past interest to compound in the first year. Enter your own rate and time above to see your number.

How do I calculate compound interest?

Use A = P(1 + r/n)^nt: divide the annual rate by the number of compounding periods a year, add 1, raise it to the number of periods, and multiply by the principal. The calculator above does it for you — pick “compound interest” and a compounding frequency.

Does compounding daily earn much more than monthly?

Only a little. On $10,000 at 5% for 3 years, monthly compounding gives $11,614.72 and daily compounding gives $11,618.22 — $3.50 more. The rate and the time matter far more than the compounding frequency.

Is this interest calculator for loans or savings?

Both — the maths is the same. For savings, the interest is what you earn. For a loan, the same formula shows the interest cost, though most real loans use the amortization formula on the loan calculator page, where each monthly payment covers interest and part of the principal.

Sources and method. Standard loan amortization formula: monthly rate = annual rate / 12; monthly payment = P × r(1+r)ⁿ / ((1+r)ⁿ − 1). Simple interest I = P × r × t; compound interest A = P(1 + r/n)^nt. Rates in the examples on this page are examples only, not live market rates. Results are estimates, not financial advice.

Estimate, not financial advice. This calculator uses the numbers you enter and the standard amortization formula. Your lender’s figures, fees and payoff rules can differ. Check the loan agreement and talk to a financial professional before you borrow.