I would approach a switch with extreme caution........

In special situations, switching from C to S could be very appropriate.

However, one must be very careful that the circumstances would be beneficial.

For example……..

If the C corp were set up with the sole method of extracting deductible income from it being salaries, ie compensation, then that could be a problem....and probably the C corp should not have been used anyway.

Further, if the only reason was to shelter income from SE tax, or to get a deferral on tax at the old corporate rate of 15%, then, again, probably a C corp should not have been used anyway.

C corps SHOULD have been used to internally finance things such as the purchase of personally-owned, or S corp-owned, land...…….and therefore rentals still exist as the method to siphon off earnings and avoid SE tax.....and, such rentals are subject to the 20% 199A deduction.

Employee benefits such as meals and lodging still exist for C corps...…..although somewhat modified now under the new law...….and if there is only one employee, the ACA restrictions on medical payments including those out-of-pocket payments such as non-insurance payments (sec 105) have never been restricted.  Further, the medical premiums for even multiple ees situations still exist for the owner/operator, and are fully deductible, ie by-passing the SE tax problem.

C corps still have dollar-for-dollar net operating loss carryforwards, although the use is now limited to 80% of taxable income to the carryforward year.  This obviously continues to allow the game of creating losses in the corps, by paying larger salaries to the individual in order to consume the standard deductions.

One still gets the effect of internal financing...…...albeit at 21% instead of 15%.  But remember that the corp rate SHOULD BE, if proper planning is occurring, only a temporary rate, with a corresponding deduction of 21% being taken when the sheltered income is ultimately pulled to the personal return.

None of this is available with an S corp.  All of the income from the S corp is taxed at the personal rate, which most likely would be less than 21%...….but no capacity to regulate losses from weak years, no employee benefits for shareholders, no capacity to manage NOLs, etc.

In summary, if one focuses primarily on the rate differences, then one is not taking advantage of the capacities of the C corp anyway...…..and then one has to question why be incorporated anyway.

Corporations have always been merely holding buckets...…...holding income for a "temporary" period...….before it can be transferred to the personal return.  The question, then, is one of making use of that deferral during the "temporary" period.

Be cautious.