Interest Calculator
Calculate simple and compound interest. Free, no signup.
How It Works
Enter the principal amount, annual interest rate, number of years, and compounding frequency. Click Calculate to see the final amount and total interest earned.
Simple vs Compound Interest
Simple interest is calculated only on the principal. Compound interest is calculated on the principal plus accumulated interest, meaning your money grows faster. The more frequently interest compounds (monthly vs annually), the more you earn.
How Compounding Frequency Adds Up
These are the final amounts for $10,000 at a 5% annual rate over 10 years, using each compounding option. The differences are small but grow with larger balances and longer terms:
| Compounding | Final amount |
|---|---|
| Simple interest | $15,000.00 |
| Annually | $16,288.95 |
| Quarterly | $16,436.19 |
| Monthly | $16,470.09 |
| Daily | $16,486.65 |
Frequently Asked Questions
How do I calculate compound interest?
Enter the principal, annual rate, and number of years, then choose how often interest compounds. The calculator applies the formula A = P (1 + r/n) raised to the power n times t, and shows the final amount and the total interest earned.
What compounding frequencies can I choose?
You can compound annually, quarterly, monthly, or daily, or select simple interest for no compounding. Monthly is the default. More frequent compounding produces a slightly higher final amount for the same rate and term.
What is the difference between simple and compound interest?
Simple interest is calculated only on the original principal, so it grows in a straight line. Compound interest is calculated on the principal plus previously earned interest, so the balance grows faster the longer it is left to compound.
Does it include regular deposits or contributions?
No. This calculator grows a single lump-sum principal and does not add recurring monthly or yearly contributions. Enter the starting amount and it shows what that amount alone becomes over the term.
Is my financial data kept private?
Yes. Every calculation runs in your browser using JavaScript, and nothing you type is sent to a server or stored. It also works offline once the page has loaded.