If your return wasn't filed by the due date (including extensions of time to file):
您可能会因为未报税而被处以罚款，除非您有合理的原因而未能及时报税。若没有在原来的申报截止日期前付清税款（无论是否有延缓申报时间），也可能会因未付清税款而受到罚款，除非您有合理的原因而未能及时缴清欠款，或者因为极度困难并且国税局已经批准您的申请表1127【申请因极度困难而延缓缴税期限】(Form 1127, Application for Extension of Time for Payment of Tax Due to Undue Hardship) 。
You may be subject to the failure to file penalty, unless you have reasonable cause for your failure to file timely. Tax not paid in full by the original due date of the return (regardless of extensions of time to file) may also result in the failure to pay penalty, unless you have reasonable cause for your failure to pay timely, or the IRS has approved your application Form 1127 (PDF), Application for Extension of Time for Payment of Tax Due to Undue Hardship).
Interest is charged on taxes not paid by the due date, even if you have an extension of time to file, and is also charged on penalties. There's no penalty for failure to file if you're due a refund. However, you risk losing a refund altogether if you file a return or otherwise claim a refund after the statute of limitations has expired.
An original return claiming a refund must be filed within 3 years of its due date for a refund to be allowed in most instances. After the expiration of the three-year period, the refund statute prevents the issuance of a refund check and the application of any credits, including overpayments of estimated or withholding taxes, to other tax years that are underpaid. However, the statute of limitations for the IRS to assess and collect any outstanding balances doesn't start until a return has been filed. In other words, there's no statute of limitations for assessing and collecting the tax if no return has been filed.