Use this free interest calculator to calculate simple and compound interest quickly and accurately.
💰 Interest Calculator
How to Use This Calculator
Enter the principal amount, interest rate, and time period. The calculator will show the interest earned and total amount.
What is an Interest Calculator?
An interest calculator helps you calculate how much interest you earn or pay over time. It is useful for loans, savings, and investments. By entering the principal amount, interest rate, and time, you can instantly see the total interest and final amount.
Types of Interest
There are two main types of interest:
Simple Interest
Simple interest is calculated only on the original amount.
Compound Interest
Compound interest is calculated on the original amount plus previously earned interest.
Your current calculator uses simple interest, but both concepts are important to understand.
Interest Formula Explained
Simple Interest Formula:
Interest = (Principal × Rate × Time) ÷ 100
Total Amount:
Total = Principal + Interest
Where:
- Principal = initial amount
- Rate = annual interest rate (%)
- Time = number of years
Example Calculations
Example 1:
Principal: $1,000
Rate: 5%
Time: 2 years
Interest: $100
Total: $1,100
Example 2:
Principal: $5,000
Rate: 7%
Time: 3 years
Interest: $1,050
Total: $6,050
Example 3:
Principal: $2,000
Rate: 10%
Time: 1 year
Interest: $200
Total: $2,200
Where Interest Calculations Are Used
Interest calculations are used in:
- Loans and credit cards
- Savings accounts
- Investments
- Mortgages
- Financial planning
Understanding interest helps you make better financial decisions.
Why Use This Interest Calculator?
This tool helps you quickly estimate interest without doing manual calculations. It saves time, reduces errors, and gives clear results instantly.
Important Note
For longer periods or accounts that add interest more than once, compound interest is usually the more relevant model. Use our Compound Interest Calculator when you need to include compounding frequency.
FAQs
What is interest?
Interest is the cost of borrowing money or the return on savings.
How do you calculate simple interest?
Multiply principal, rate, and time, then divide by 100.
What is total amount?
It is the original amount plus the interest earned.
How to choose the right interest method
Choose simple interest when interest is calculated only on the original principal. Choose compound interest when each new interest calculation includes interest already added to the balance. The difference becomes more important as the rate, time or compounding frequency increases.
Example: £1,000 at 5% simple interest for three years earns £150, giving a total of £1,150. If the same amount compounds annually, the estimated total is £1,157.63. The calculator keeps the rate fixed for the whole period and does not automatically include deposits, withdrawals, fees, tax, inflation or a changing interest rate.
How the result is checked
Simple interest is checked with I = P × r × t, where P is principal, r is the annual rate written as a decimal and t is time in years. Compound totals are checked with A = P(1 + r/n)nt, where n is the number of compounding periods per year. Small differences can occur when a bank rounds daily, uses a different day-count convention, or changes the rate during the term.
Source and review note
For an independent comparison, see the US Securities and Exchange Commission’s compound interest calculator. This page was last reviewed on 19 August 2026 by Badar Ashfaq. It is an educational estimate, not savings, lending or investment advice. See our editorial policy and testing method.