This report describes Mathematica’s evaluation design of the Promoting Opportunity Demonstration (POD). Congress directed the Social Security Administration to carry out POD to test a benefit offset formula for Social Security Disability Insurance beneficiaries. POD tests a simplified set of work rules that replaces the cash cliff with a more gradual ramp, which we refer to as a benefit offset. The offset formula reduces benefits by $1 for every $2 of earnings in excess of a Trial Work Period level (defined as $850 in 2018). The evaluation of POD is a randomized controlled trial that tests two versions of POD rules and current rules for beneficiaries who volunteer for services. The two treatment arms use the same offset formula but differ in what happens to beneficiaries whose benefits are offset to zero. The evaluation also includes a control arm that is subject to current law rules. The design report details Mathematica’s comprehensive evaluation approach including process, participation, impact, and cost-benefit analyses. The evaluation will provide information on the outcomes for at least 9,000 subjects who meet the eligibility criteria, reside in select areas of eight POD states, and volunteer for the demonstration.