How long do I have to file an amended individual income tax return for a state change?

If your change decreases the tax due to Illinois and you want a refund, you must file  Form IL-1040-X, Amended Individual Income Tax Return, within

  • three years after the extended due date, 
  • three years after the date your original return was filed, or 
  • one year after the date your Illinois tax was paid, whichever is latest.

If your change increases the tax you owe to Illinois, you should file Form IL-1040-X and pay the tax, penalty, and interest as soon as you realize that it is owed.

If you have additional inquiries, you may submit them to the Questions, Comments, or Request form.