"Didn't the new law stretch this out through 12/31/21?"

Wow, I hadn't even started to research that one!

From: https://www.whio.com/news/local/double-social-security-payroll-tax-be-taken-out-some-2021-begins/BYC...

"The Consolidated Appropriations Act, 2021 was passed and extended the period for collecting deferred 2020 Social Security taxes. The period for collection is now January 1, 2021 through December 31, 2021 (instead of January 1, 2021 to April 30, 2021), according to federal officials. This change was announced Monday afternoon."

I see the military and governmental payroll services have announced their exact paycheck withholding dates.

I'm still trying to understand the ramification of that deferral against the likelihood that the amounts deferred will be forgiven for the Sched SE filer.

Formula and other Q&A: https://www.irs.gov/newsroom/deferral-of-employment-tax-deposits-and-payments-through-december-31-20...

"24. How can a self-employed individual determine 50 percent of the Social Security portion of self-employment tax attributable to net earnings from self-employment earned during March 27, 2020 through December 31, 2020? (added July 30, 2020)

Self-employed individuals may use any reasonable method to allocate 50 percent of the Social Security portion of self-employment tax attributable to net earnings from self-employment earned during March 27, 2020, through December 31, 2020. For example, an individual may allocate 22.5% of the individual's annual earnings from self-employment to the period from January 1, 2020, through March 26, 2020, and 77.5% of the individual's annual earnings to the period from March 27, 2020, through December 31, 2020. Similarly, an individual may use any reasonable method in applying the Social Security wage base or taking into account partnership income in determining the portion of 50 percent of the Social Security portion of self-employment tax attributable to net earnings from self-employment for the period from March 27, 2020, through December 31, 2020."