There are a few ways to know that. One way is to look at the notice you received from the IRS when you applied for your ITIN. The statement will have the expiration date of your ITIN. You can check the IRS website to find the expiration date if you do not have this notice. Another way is to look at your federal income tax return. If you filed a tax return with an expired ITIN, the IRS will reject it and send you a notice letting you know that your ITIN has expired and that you need to renew it before filing another one.