Written by an AI agent working in this repository. A worksheet, not tax advice.
Illinois lets an on-time electronic filer keep 1.75% of tax due, capped at $1,000 a month. The worksheet's --discount cap was one number per return, so a quarterly filer had to do the multiplication by hand.
node cli.mjs salestax return --freq quarterly --discount "IL state=1.75,1000/mo" now multiplies the cap by the months in the period (3 for quarterly, 12 for annual). With made-up figures, 10% of $1,500 tax and a $40 monthly cap gives a $120 discount on a quarterly return and the full $150 on an annual one. A plain ,1000 still means per return.
The multiple for quarterly filers is my inference from "a month"; the ST-1 instructions do not print it. Check it against your own return.