Tax Extension Deadline and Federal Filing Rules after October 15

Under Internal Revenue Code § 6601, interest generally accrues on unpaid tax from the original payment due date until the balance is paid. An extension of time to file does not postpone that interest calculation.

Taxpayers who timely request an extension generally avoid the failure-to-file penalty through October 15 if they file by the extended deadline. An unpaid balance may still be subject to the failure-to-pay penalty under 26 U.S.C. § 6651(a)(2). The extension postpones the filing deadline rather than the payment deadline, so interest and any applicable late-payment penalty can continue during the extension period.

The failure-to-file penalty generally accrues at 5 percent of the unpaid tax for each month or part of a month the return is late, up to 25 percent. When the failure-to-file and failure-to-pay penalties apply in the same month, § 6651(c)(1) generally reduces the filing penalty by the amount of the failure-to-pay penalty imposed for that month.

• Failure-to-File Rate: Generally 5 percent per month or part of a month on the unpaid tax subject to the penalty.
• Failure-to-Pay Adjustment: The failure-to-file rate is generally reduced by 0.5 percentage points when both penalties apply for the same month.
• Combined Monthly Rate: The overlapping rates are generally 4.5 percent for failure to file and 0.5 percent for failure to pay during the first five months.
• Failure-to-File Maximum: The failure-to-file penalty generally reaches a maximum of 25 percent of the unpaid tax subject to that penalty.

When a required return remains unfiled, the IRS may use substitute-return procedures under 26 U.S.C. § 6020(b). The agency can rely on available information, including third-party reporting documents such as Forms W-2 and 1099, when determining a proposed tax liability.

For individual taxpayers, an SFR generally includes the standard deduction but may omit itemized deductions, elections, and credits that require information or action from the taxpayer. An SFR examination may lead to a Notice of Deficiency before assessment, followed by collection procedures if an assessed liability remains unpaid. These procedures can become part of broader Tax Delinquency and Penalties issues.

Under 26 U.S.C. § 6651, the failure-to-file and failure-to-pay penalties contain reasonable-cause exceptions when the statutory requirements are satisfied. The IRS generally considers whether the taxpayer exercised ordinary business care and prudence but was nevertheless unable to file or pay on time.

Relevant circumstances may include serious illness or incapacitation, destruction of records by fire or natural disaster, or an inability to obtain necessary records despite reasonable efforts. The IRS evaluates reasonable cause from the facts and circumstances rather than treating any single circumstance as automatic grounds for relief.

Administrative penalty relief may also be available under applicable IRS criteria, including First Time Abate for qualifying taxpayers. Eligibility depends on the penalty involved and the taxpayer's filing, payment, and prior-compliance history.

Filing a past-due return generally stops additional failure-to-file penalty months from accumulating, although penalties already incurred and other amounts may remain due. Taxpayers who cannot immediately pay the assessed balance may qualify for an installment agreement under 26 U.S.C. § 6159.

Section 7122 separately authorizes an Offer in Compromise when the applicable statutory and regulatory requirements are satisfied. Grounds can include doubt as to liability, doubt as to collectibility, or effective tax administration under the governing Treasury regulations.