@Anonymous
For a W-2 employee.........as soon as you become a WI resident....You fill out an IL-W-5-NR and submit to the IL employer. Doing so allows the employer to not withhold any IL taxes at all from that point on. You don't give that to the employer until you actually move. (Payroll department and/or HR if they have one)
https://www2.illinois.gov/rev/forms/withholding/Documents/currentyear/il-w-5-nr.pdf
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Then, you find the procedure for sending in quarterly estimated tax payments directly to the WI tax department, and send them quarterly payments instead of the employer withholding normally done . (in order for the employer to withhold WI taxes, they have to register in some way with WI....and not all employers are able, or willing to do so..normally small IL employers, with few WI resident employees, won't want to bother ).
FAQs and link to the Instructions, and to the 2019 Forms 1-ES are here:
https://www.revenue.wi.gov/Pages/faqs/pcs-estpay.aspx
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IF you move in 2019, then you will have to file a-part-year IL and a part-year WI tax returns, and since it is Dec, may not need to file/pay WI estimates for 2019 for the one partial month remaining....probably too small to bother.
But if you don't move until sometime in 2020, then you will need to pay the WI-estimates according to the quarter in which you move (Check the dates in the WI FAQ above). You do that directly with WI. You can't have TurboTax arrange those payments. Just make sure you send WI the 2020 estimated forms at that time, not 2019 forms.
For the IL and WI part-year tax returns, IL will tax you only on ALL your income for the portion of the year you were an IL resident, and WI will tax you the remaining. (keep monthly records of all income, interest, dividends, cap gains...etc. You'll need them in the year you actually move to WI). In subsequent years, then it's only the WI tax return that needs to be filed (as long as you don't have property in IL that you rent out, or run some other personal non-W2 business in IL)
____________*Answers are correct to the best of my knowledge when posted, but should not be considered to be legal or official tax advice.*
