You will basically be filing a final SCH C with a closing date of at least one day before the S-Corp became active. Any and all assets, inventory and vehicles are removed from the SCH C business "for personal use". For the SCH C business to be closed, it must have no assets, no inventory, and no vehicle use - even if that vehicle use is less than 100% business use.
When starting the firsst 1120-S for the S-Corp, then opening date of the business will be the same exact date you opened the SCH C business. Doesn't matter if it was years ago either. Then add you assets with the same exact in-service date you used on the SCH C.
Now understand these dates, as they matter big time. You get them wrong, and darn near everything will be screwed up - especially depreciation on business assets.
Date the business opened - This is the date the business originally opened exactly as shown on the very first SCH C that you filed - even if it was years ago.
Date the business incorporated - At least one day after the SCH C business was closed and ceased to exist.
Be aware that as an S-Corp, you are required by law to take a minimum draw from the business every year. You are also required to make quarterly reports to the state the S-Corp is registered in. This state reporting has nothing to do with taxes.
Finally, the 1120-S corporate return is due by March 15 of every year. Late fees for filing the corporate return late are presently set at $205 per month, per owner. So while your personal 1040 return may have a filing deadline of Apr 15, the filing deadline for the corporate return is March 15. Be aware of that, as filing late can and will get costly.
