Using Calconic (https://www.calconic.com) you can easily add a loan calculator to your website. It is super easy to use and requires absolutely no prior programming experience. As well, it has a bunch of ready-to-use templates for mortgage and loan calculators. Not to mention that the calculator can be easily embedded to your Squarespace website. By following the link you can find more information about it - https://www.calconic.com/knowledge/adding-custom-calculator-widget-to-squarespace-website.