Pre-tax 401(k) employee deferrals are contributed on a tax-deferred basis. That means that the amount contributed is subtracted from your taxable income for the year. You will, however, be subject to tax on both the contributions and any associated earnings when you subsequently withdraw these amounts.

Roth 401(k) contributions are contributed after taxes are paid. However, both the contributions and the gains are tax-free when you subsequently withdraw them.

Pre-tax employer contributions are similar to Pre-tax 401(k) employee deferrals in that they are contributed on a tax-deferred basis; however, these are contributions that are made by your business, as opposed to you. These amounts are subject to higher dollar limitations than Pre-tax 401(k) employee deferrals, but are limited to 25% of your eligible taxable income (after pre-tax contributions). Like Pre-tax 401(k) employee deferrals, the amount contributed is subtracted from your taxable income for the year, but you will be subject to tax on both the amount of the Pre-tax employer contributions made and any associated earnings when you subsequently withdraw these amounts.

After-tax employee contributions are fairly uncommon, as they are contributed after taxes are paid. Unlike Roth 401(k) contributions, while you you will not pay taxes on the amounts contributed when you subsequently withdraw them, you will be taxed on any gains associated with these contributions. Typically, After-tax employee contributions are made by those who wish to make an "in plan Roth conversion." You should consult a tax professional if you are considering this option.

Catch-up contributions allow people aged 50 or older to make additional contributions (up to $7,500 in 2024) to their 401(k) after reaching the maximum annual contribution amount ($23,000 in 2024). Catch-up contributions are made through elective salary deferrals.