Embed the Simple Interest Calculator
Interest charged on the principal only, with the compound figure beside it so the gap the two produce over the same term is visible rather than assumed. Set the values it should open on, then copy the iframe. Your visitors can change them; the widget recomputes against Rule Calculator and never touches your page.
Opening values
Set what the widget shows before anyone touches it. Leave a field as it is and it stays out of the URL.
Preview
Paste this
<iframe src="https://rulecalculators.com/embed/simple-interest" width="100%" height="780" style="border:1px solid #e5e5e5;border-radius:12px" loading="lazy" title="Simple Interest Calculator"></iframe>
<p style="font:13px/1.5 system-ui,sans-serif;color:#666;margin:6px 0 0"><a href="https://rulecalculators.com/calc/simple-interest" style="color:#666">Simple Interest Calculator</a> by <a href="https://rulecalculators.com" style="color:#666">Rule Calculator</a></p>Free for commercial use. The one condition is the credit link inside the widget, which is how the calculator stays free. Want the numbers in your own markup instead? The same calculator is a JSON endpoint, or see the full Simple Interest Calculator page with its sources and working.