A Solo 401k is a retirement savings plan for people who work for themselves or run a small business with no full-time employees other than a spouse. It lets you save for the future in two ways—both as the “employee” and the “employer”—which means you can often put away more money than you could with other types of retirement accounts. You can choose to make contributions on a pre-tax basis (which lowers your taxable income now) or after-tax with a Roth option (so you can take tax-free withdrawals later). A Solo 401k also gives you a lot of flexibility in how you invest your savings and only requires extra IRS reporting once the account grows past a certain size.