Interest Calculator
Calculate simple or compound interest earned on any principal amount.
Interest Calculator
Calculate simple or compound interest earned on any principal amount.
Simple & Compound Interest
ℹ️ Compound interest earns significantly more than simple interest over long periods
Disclaimer
Results provided by this calculator are for informational and educational purposes only. They are based on the values you enter and standard formulas, and should not be considered financial, medical, legal, or professional advice. Always consult a qualified professional before making important decisions based on these results. Roughtools makes no warranties regarding the accuracy or completeness of these calculations for your specific situation.
Frequently Asked Questions
Pro Tips
Compound interest is asymmetric: it helps you dramatically as an investor, but hurts you dramatically as a borrower on high-rate debt. Eliminate high-rate debt first.
The effective annual rate (EAR) is always higher than the nominal rate when compounding is more frequent than annually. Monthly compounding at 6% nominal = 6.17% EAR.
Comparing investments with different compounding frequencies? Convert all to Effective Annual Rate first for a true apples-to-apples comparison.
High-yield savings accounts and CDs often advertise APY (annual percentage yield), which is the EAR — it accounts for compounding. Lower APR means less interest paid on loans.
When to Use This Calculator
Compare interest earned between accounts with different rates to pick the best place for your emergency fund.
Calculate exact interest earned on a certificate of deposit or bond before locking in your money.
See the total interest you will pay over the life of any loan — a figure lenders often don't highlight upfront.
Visualise the difference between simple and compound interest over time to understand why compound matters.
Estimate final value of an investment given an assumed interest rate and time horizon.
About the Interest Calculator
This interest calculator computes both simple interest and compound interest simultaneously so you can compare them side by side. Enter the principal amount, annual interest rate, and time period to see total interest earned and final balance under both methods. Ideal for understanding savings accounts, CDs, loans, and investment returns.
How to Use the Interest Calculator
- 1
Enter the principal amount (starting balance or loan amount).
- 2
Enter the annual interest rate as a percentage.
- 3
Enter the time period in years.
- 4
See simple interest and compound interest results side by side.
- 5
Note the growing gap between the two methods over longer periods.
Related Calculators
View all →Compound Interest Calculator
Calculate investment growth with daily, monthly, or yearly compounding.
Simple Interest Calculator
Calculate simple interest earned on a principal over a set period.
Savings Calculator
Calculate how much you'll save over time with regular deposits and interest.
Loan Calculator
Calculate monthly loan payments and total interest for any loan type.
APR Calculator
Calculate the annual percentage rate for any loan including fees.
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