What are the differences between contributing to a pre-tax vs after-tax 401k, and how do these choices impact my retirement savings?

Contributing to a pre-tax 401(k) reduces your taxable income now, but you'll pay taxes on withdrawals in retirement. After-tax 401(k) contributions are made with money that has already been taxed, so withdrawals in retirement are tax-free. Your choice impacts how much you pay in taxes now and in retirement, affecting your overall retirement savings.