% Interest Calculator
Calculate simple or compound interest on a deposit or loan, and see the total interest earned or owed.
Interest Details
Your Result
Compound interest reinvests earned interest, so growth accelerates over time.
How the Interest Calculator Works
Interest is the cost of borrowing money or the reward for saving it. This calculator supports both simple interest, which grows at a constant rate, and compound interest, which grows faster because interest is earned on previously accumulated interest.
Formulas
Compound Interest: A = P × (1 + r/n)^(n×t), I = A − P
Where P is the principal, r is the annual interest rate (as a decimal), t is the time in years, n is the number of times interest compounds per year, and A is the final amount.
Frequently Asked Questions
What is the difference between simple and compound interest?
Simple interest is calculated only on the original principal, while compound interest is calculated on the principal plus any interest already earned, causing it to grow faster over time.
Does a higher compounding frequency always mean more interest?
Yes. For the same nominal rate, compounding more frequently (e.g., daily vs. annually) results in a slightly higher effective return because interest is added to the balance more often.
How do I use this as a daily interest calculator?
Select "Compound" mode and choose "Daily" from the compounding frequency dropdown. The calculator will apply the formula A = P × (1 + r/365)^(365×t), matching how many savings accounts and credit cards compute daily interest.
Can this calculator be used for loans?
Yes, the same formulas apply whether you're calculating interest earned on a deposit or interest owed on a loan.
How much will my money be worth in a few years at a fixed interest rate?
Enter your starting amount as the principal, the annual rate, and the number of years, then choose simple or compound interest depending on how your account or investment actually grows. The calculator shows both the interest earned and the total final amount.