This is via an administrator for the HPSP Facebook page:
Updated for Academic Year 2020-21
FYI regarding the stipend, for budget planning purposes each year:
Per Section 2121, Title 10, USC, the stipend increases each year on 1 July by the same percentage that base pay increased for the current calendar year over the previous calendar year; for AY20-21, then, the stipend will be $2465.73.
Regarding taxes, you can determine your monthly federal withholding based on your allowances claimed using the 2020 withholding tables (consult your state for a similar resource). Per Chapter 41, Volume 7A, DoD Financial Management Regulation, the stipend is subject to federal and state withholding but not FICA; base pay, but not BAH or BAS, earned during ADT is subject to federal and state withholding and to FICA (6.2% for Social Security, 1.45% for Medicare).
Section 2121, Title 10, U.S. Code
Miltary Pay Charts
2020 Federal Income Tax Withholding Tables
2020 FICA Rates
IRS Tax Topic on Social Security and Medicare taxes.
www.irs.gov
Volume 7A, DoD Financial Management Regulation