Responsive mortgage repayment calculator with custom radio buttons.

What are you most proud of, and what would you do differently next time?

I like the custom radio buttons which are created only using css. The actual input type="radio" is hidden, the visible button is created with ::before.

What specific areas of your project would you like help with?

I'm not sure if the calculation is correct, but the result is the same with the example values. Please help correcting the algorithm if it's incorrect.