* You pay 7.65% more in medicare taxes
* You are probably eligible for the new (as of 2018) 20% pass through deduction
* You can possibly deduct expenses (hardware, software, home office, mileage)
* No paid vacation/sick days/holidays (this is often around 4 weeks worth of time a year)
Finally you really have to look hard at the benefits you are missing out on. For instance, health insurance can be very expensive out of pocket. 401k matching is the other big thing you may miss out on.
Also look at how you are billing. If hourly, you may find you can't honestly bill more than 6 hours of work a day. Compare that to salary which often assumes 8 hour work days regardless of work performed. This can be worked around if you bill a day rate instead.