If you filed an amended return with the Internal Revenue Service or another state, you generally must also file an amended Wisconsin return within 90 days. You need to file an amended Wisconsin return if the changes affect your Wisconsin income, any credit, or tax payable. Use Form 1X to file an amended Wisconsin return.
When to File Form 1X only after you file your original return.
Generally, a claim for refund must be filed within 4 years after the unextended due date of your original return (for example, April 15, 2015, for 2010 calendar year returns).
However, a claim for refund to recover all or part of any tax paid as a result of an office or field audit may be filed within 4 years after the date assessed. This applies only if you paid the tax and did not file a petition for redetermination (written appeal).
Where to File Mail your Form 1X to the Wisconsin Department of Revenue at:
PO Box 8991
Madison WI 53708-8991
You may be able to electronically file your Form 1X using Wisconsin e-file. This free e-file service is available from the department's web site at www.revenue.wi.gov. Your form can be submitted electronically after you complete it. You may also be able to e?file Form 1X through your software package.