If I form a new single-member LLC in December 2020, when do I need to start filing taxes? As this will be a single-member LLC, I guess taxes can be paid under Schedule C of personal income taxes. But, do I need to pay taxes monthly, quarterly or yearly?
Your LLC will issue you a K-1 which you report on your Sch C. You should make quarterly estimated payments. TurboTax can calculate those payments and provide vouchers for you to use when you send your payments.
@Bsch4477 . A single member LLC is a disregarded entity unless there is an election to be taxed as an association which would then be either a C corp or an S corp. The facts do not indicate this has been done.
As such, the single member LLC, since it is disregarded, will be reflected on Schedule C as noted by the poster. There is NO K-1 that will or needs to be issued.
In addressing the tax question, you need to monitor your taxable income and make quarterly estimated tax payments. You may want to discuss this with a tax professional so you get started down the right path in your first year.