1. health insurance
2. stock options
3. so-called "employer's contribution" to social security
4. 401k employer match contributions
5. sick leave
6. vacation
7. maternity/paternity leave
8. stock purchase plan
9. unemployment insurance taxes
10. 2 weeks severance pay
11. holiday pay
12. various legal rights contractors don't have
13. employer provided equipment that a contractor would be expected to provide
Here's the first hit on google:
https://www.bankrate.com/finance/financial-literacy/the-valu...
#1,3,4,5,6,7,9,11 add up to at most 30%
And #2,#8,#12,#13 could be worth 10%. I don’t think #10 is a guaranteed benefit, and usually is in exchange for forgoing any other grievances you might have against employer.
But that would be restricting it to highly paid, in demand professions. For other people (upwards of 80% of the US), many of the items on that list don’t apply to them, so I don’t see how it would cost 40% more for an employee versus contractor.
https://www.mysolo401k.net/solo-401k/solo-401k-contribution-...
A sole proprietorship is almost as easy to file as a 1099, and a good choice when a liability veil would be easily be peirced (as you're representing your own skills)
I... think you may be mistaken.
I've heard that big companies have a total overhead of 40% for a worker, and that might be true once you factor in the cost of middle management and office space, though again it would vary a lot by pay (I imagine office space costs a large portion of a less well paid salary. Around here, quarter-million dollar a year SWEs get the same tiny desks you'd expect of someone making 1/4 that.)
but I've got a reasonable idea of what benefits cost, and it's nowhere near 40%, at least for a SWE in my jurisdiction, where total comp is so high and the benefits are... comparatively minimal.