For (single) self-employed people making between ~$85k and $137k, the marginal federal tax rate they face is a little under 40%, with 24% from your link, ~12% from Social security, and ~3% from Medicare. This excludes the effect of phaseouts of various deductions (eg, student loan interest), which can easily drive that higher while remaining within the context of federal taxation only.

Everybody forgets about Social Security and Medicare. Writing out the federal marginal rates for the different income brackets with SS and Medicare included is very eye-opening.

The other thing people forget are means-tested aid programs each of which is seemingly designed without considering interactions with the other ones. There are various places in the 0-$40k income range where people face >100% marginal rates due to the combination of actual taxes and benefit phaseouts...