A Roth deferral is money that a person puts in a Roth investment account to save for later in life, usually retirement.There are two types of Roth accounts: a standard Roth Individual Retirement Account, or IRA, and a Roth 401(k). Payments to either account must be made with post-tax dollars.here are several key differences between Roth IRA and 401(k) plans, but a Roth deferral happens under either one. The main idea behind a deferral is to save money in a growth account that can be used later in life without incurring a tax penalty.