Simple Interest Calculator
Calculate simple interest earned on a principal over a set period.
Simple Interest Calculator
Calculate simple interest earned on a principal over a set period.
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 Simple Interest Calculator
This simple interest calculator applies the formula I = P × r × t to compute interest earned or owed on any principal over a specified period. Enter any three of the four variables (principal, rate, time, interest) to solve for the unknown. Used for short-term loans, Treasury bills, and basic financial literacy — runs entirely in your browser.
How to Use the Simple Interest Calculator
- 1
Enter the principal amount (initial sum of money).
- 2
Enter the annual simple interest rate as a percentage.
- 3
Enter the time period in years (or months — convert to years by dividing by 12).
- 4
See the interest earned and the final total amount instantly.
- 5
To solve for principal or rate, enter the known values and leave the target blank.
Related Calculators
View all →Interest Calculator
Calculate simple or compound interest earned on any principal amount.
Compound Interest Calculator
Calculate investment growth with daily, monthly, or yearly compounding.
Loan Calculator
Calculate monthly loan payments and total interest for any loan type.
Savings Calculator
Calculate how much you'll save over time with regular deposits and interest.
APR Calculator
Calculate the annual percentage rate for any loan including fees.
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