Some exceptions: credit card details, city, state, and ZIP fields. I’m not mentioning the Name field because it should be a single Full Name field, instead of First Name and Last Name.

To quote Baymard (source):

Forms with multi-column designs often lead users to:


And actually, Shopify implemented this, their checkout form is a single column (except for the name fields and the country / state / zip.

Their second column has a summary, discount code, subtotal, shipping, and total… and a different background color.