This is the straightforward version. The result field is always visible, and the monthly repayment appears the moment you press Calculate or updates on its own as soon as you change any of the figures, so you can try a different rate or term and watch the number move. It arrives on the page already showing a worked example, and if a field is left empty or holds something that isn't a number, the calculator says so instead of quietly doing nothing. Best when the answer itself is what you want visitors to walk away with.

This is the lead-capture version. Pressing Calculate checks the figures and works out the repayment, but the number is never shown on the page. Instead, the visitor is asked for an email address, and Show my repayment sends the result straight to their inbox, with the page confirming it is on its way. Because the answer is delivered by email rather than displayed, only a genuine, working address earns it, so the addresses you collect are ones you can actually reach. A reCAPTCHA and a consent check box come as part of the gate. Best when the calculator is doing a job for your marketing as well as for the visitor.