Simple Interest Calculator
Enter your principal, rate, and time below for an instant, non-compounding interest total -- no calculator tricks, just I = P x r x t.
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- Your numbers stay in your browser
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This is a general estimate, not financial, investment, or tax advice.
Built by Cedrick Reese · How this is verified
How to Use This Calculator
Enter your principal, your annual interest rate, and a time period in months or years. The result shows interest earned and the total amount, calculated as simple interest, not compound -- this tool doesn't compound at all, unlike the Savings Interest Calculator.
Simple interest vs. compound interest
Simple interest is calculated only on your original principal: I = P × r × t. Compound interest, which is what most everyday savings accounts actually use, is calculated on your principal plus any interest you've already earned. This calculator uses the simple version, which is useful for loans, short-term notes, and financial products that are explicitly simple-interest. For a compounding savings account, use the Savings Interest Calculator instead.
For example: a $5,000 principal at a 4.5% annual rate for 3 years earns $675.00 in interest (5,000 × 0.045 × 3), for a total of $5,675.00 -- no compounding involved, so the math stays this simple regardless of the term.
Frequently asked questions
What's the difference between simple and compound interest?
Simple interest is calculated only on the principal. Compound interest is calculated on principal plus previously earned interest, so it grows faster over time. Use the Savings Interest Calculator for the compound version.
When is simple interest used instead of compound interest?
Simple interest commonly applies to some loans, short-term notes, and specific bonds. Most everyday savings accounts compound instead.
How do I convert months to years in the formula?
Divide the number of months by 12 to get years, then multiply by the annual rate. This calculator does that conversion automatically when you select Months.
Does a savings account ever actually use simple interest?
Rarely for standard savings accounts, since most compound at least monthly. Check the Savings Interest Calculator for the compounding version.
Sources
- Simple interest formula (I = Prt) — Vertex42
How This Calculator Is Verified
Built by Cedrick Reese. The simple interest formula (I = Prt) is checked against Vertex42's published version, and the worked example on this page is run by hand before it goes live.
Last reviewed: August 25, 2026