What is the difference between pre-tax and Roth contributions in retirement savings accounts?

The main difference between pre-tax and Roth contributions in retirement savings accounts is how they are taxed. Pre-tax contributions are made with money that has not been taxed yet, so you will pay taxes on the money when you withdraw it in retirement. Roth contributions are made with money that has already been taxed, so you won't have to pay taxes on the money when you withdraw it in retirement.