Simple Interest Calculator
I = Prt, with what compounding would have added.
Work out Simple Interest. I = Prt, with what compounding would have added. Shows the working, not just the answer.
Simple interest
$500.00
Total $1,500.00
Simple interest is I = Prt — interest on the principal only, never on interest already earned. The comparison row is the point: over 10 years at 5.00%, compounding would have added a further $128.89. Simple interest is now rare outside short-term and some auto loans; almost everything else compounds.
How the Simple Interest Calculator works
Simple interest is charged on the principal only, never on interest already earned. The comparison against compound interest is the point of this page: over a long enough term the gap becomes the larger number.
Also known as: simple interest formula · i = prt calculator · simple vs compound interest · how to calculate simple interest
Frequently asked questions
What is the simple interest formula?
I = Prt — principal times rate times time. £1,000 at 5% for 10 years earns £500.
How is it different from compound interest?
Compound interest earns interest on interest. The same £1,000 at 5% compounded annually reaches £1,628.89 rather than £1,500 — an extra £128.89 over ten years, and the gap widens as the term grows.
Where is simple interest still used?
Short-term and some auto loans, certain bonds, and many informal arrangements. Almost everything long-term compounds.
Is simple interest better for a borrower?
Yes, at the same rate — you never pay interest on interest. Comparing a simple rate directly against a compound one understates the compound cost.
Put this calculator on your own site
Free to use, on any site, commercial or not. Paste this where you want it to appear. It is a plain iframe, so it works in WordPress, Squarespace, Wix, Webflow, Ghost and anything else that accepts HTML.
<iframe src="https://www.thecalclibrary.com/embed/simple-interest-calculator" width="100%" height="640" style="border:1px solid #e2e8f0;border-radius:12px" loading="lazy" title="Simple Interest Calculator"></iframe>The only condition is that the credit line stays visible. It sits inside the frame, so you do not have to do anything to keep it.