即使您已获准得以延期申报，到期未付的税款也需加收利息，罚款也要加收利息。如果您可以得 到退税，则未报税并不会被罚款。但是，如果您在有效时限过后才报税或申请退税，您有可能损 失全部的退税款项。在大多数情况下，必须在纳税申报截止日期起三年内提交申报，才能获得退税。三年期限届满 后，退税法规禁止核发退税支票和任何优惠的申请，包括超付的预纳税金或预扣税款，其他纳税 年度少付的退税款。此外，国税局对课徵和催讨未缴税款馀额的法定追溯期是从报税表提交后才 开始。换言之，若未提交报税表，对课徵和收讨税金是没有追溯期的限制的。

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.