The SECURE Act requires defined contribution plans (e.g., 401(k)s) to give participants illustrations of their lifetime income expectation from their account balances expressed as a single life annuity or, for married participants, a joint annuity. The DOL has a interim final rule explaining how to do this. To calculate a monthly payment illustration, you need an assumed commencement date when benefits will start, an assumed age, an assumed interest rate, and other factors.