The IRS will not automatically penalize you for filing your tax return late if they owe you a refund, as they do when you owe them money. When you owe them money and are late in filing, they charge you interest. However, you need to file within three years of the due date. Otherwise, you may lose your refund.

On the Other: They Can Deny You

If you are late in filing, you can lose your refund. If you filed a tax return and later realize that you are owed a refund, the deadline for claiming your refund is three years after filing your tax return, or two years after paying your taxes, whichever comes later. The IRS can generally give you information about your refund within 72 hours after they acknowledge that they received your efiled tax return or three to four weeks after receiving your mailed return.

Bottom Line

In order to receive your refund, you must file or efile your tax return within three years of when it is due. If you don't receive your refund within 28 days from when you sent it in, you can start an online trace through the IRS at "Where's My Refund" to search your refund status. Do not fall for any scams regarding refunds. The IRS never initiates emails to you.

Source:

IRS.gov; Where's My Refund?

Efile.com; Federal IRS Extension