This is what Wisconsin says:
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What should I do if I already filed my Wisconsin income tax return and now want to file my homestead credit claim? What should I attach to my separately filed homestead credit claim?
If you previously filed your Wisconsin income tax return and now wish to file a claim for homestead credit, you should write "Income Tax Return Separately Filed" on the top of your Schedule H or H-EZ. Before mailing your Schedule H or H-EZ, attach the following behind your claim:
- Your completed 2018 rent certificate(s) and/or a copy of your 2018 property tax bill(s).
- Other homestead credit notes, schedules, or legal documents.
- Schedule GL, Gain or Loss on the Sale of Your Home, if you sold your principal residence during 2018.
- Copies of any wage statements, Forms W-2, W-2G, 1099-R, and 1098-T.
Delays to your refund will happen if all the proper documents are not attached to your homestead credit claim.
More FAQ on this credit:
https://www.revenue.wi.gov/Pages/FAQS/ise-home.aspx#home2
