illinois - on a timely basis estimates and withholding must equal 100% of 2020 tax or 90% of 2021 tax.
timely basis 1/4 by 4/15/2021 1/2 by 6/15/2021 3/4 by 9/15/2021 100% by 12/31/2021 except the fourth quarter estimate can be paid by 1/15/2022
also no penalty if the balance due after subtracting withholding only from tax liability is $1000 or less/
see IL 2210.
https://www2.illinois.gov/rev/forms/incometax/Documents/currentyear/individual/IL-2210.pdf
