Interest Calculator
Project savings or loan growth with simple or compound interest — see the final amount and total interest earned.
Input
Enter principal, rate, and years to project growth.
The Interest Calculator projects how a savings deposit or loan balance grows over time using either simple or compound interest. It shows the final amount and the total interest earned or paid, making it easy to compare accounts or understand the cost of borrowing.
How to use the Interest Calculator
- Enter the starting principal amount.
- Enter the annual interest rate as a percentage.
- Enter the time period in years.
- Pick simple or compound interest (and the compounding frequency if shown).
- Read the final balance and the total interest.
Frequently asked questions
- What is the difference between simple and compound interest?
- Simple interest is earned only on the original principal, while compound interest is earned on the principal plus previously accumulated interest. Compounding makes balances grow faster the longer the time horizon.
- How is simple interest calculated?
- Interest = principal x rate x time, using the rate as a decimal. On 1,000 at 5% for 3 years, that is 1,000 x 0.05 x 3 = 150 in interest, for a final balance of 1,150.
- How is compound interest calculated?
- Final amount = principal x (1 + rate/n)^(n x years), where n is the number of compounding periods per year. 1,000 at 5% compounded yearly for 3 years grows to 1,000 x 1.05^3 = 1,157.63.
- Does it account for regular deposits?
- This calculator projects growth on a single lump sum. For recurring contributions you would need a separate savings or annuity calculation that adds each deposit over time.