It can be more than a 20% return.
We've got kids, and after maxing DH's 401k, we are eligible for the EIC. The phase out rate is something like 21%, + our state matches EIC at 30% of federal EIC, for another 6.3%, state income tax is 4%, plus federal (for us) 10% and FICA 7.65% for a total of 48.95%.