The Power of Compound Interest Learn how to harness the power of compound interest for your investments. Related Content Self-Employed Retirement Plans Estimate the maximum contribution amount for a Self-Employed 401(k), SIMPLE IRA, or SEP. Roth 401(k) vs. Traditional 401(k) This calculator compares employee contributions to a Roth 401(k) and a traditional 401(k). What Is My Current Cash Flow? Assess whether you are running “in the black” or “in the red” each month.