Interest Rate Calculator
Find the interest rate needed to reach a savings or repayment goal.
Interest Rate Calculator
Find the interest rate needed to reach a savings or repayment goal.
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 Rate Calculator
This interest rate calculator solves for the unknown rate in any loan — given the monthly payment, principal, and term, it finds the exact annual interest rate. Enter what you pay each month and the loan details to discover the true rate you are paying. Perfect for evaluating dealer financing, credit card offers, and mystery loan rates.
How to Use the Interest Rate Calculator
- 1
Enter the original loan amount (principal) in dollars.
- 2
Enter your monthly payment amount.
- 3
Enter the loan term in months or years.
- 4
The calculator solves for the hidden annual interest rate instantly.
- 5
Compare the result against advertised rates to spot hidden costs.
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