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

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.

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