October 15 is generally the final backstop for calendar-year extension filers — there's usually no further extension available. Here's what actually happens if that date passes without a filed return.

October 15 is the extended deadline for individual and C-corp returns. Extensions delay filing, not payment — here's what's been accruing on any unpaid balance since April, and what the deadline does and doesn't fix.

September 15 was the extended deadline for calendar-year Forms 1065 and 1120-S. The penalty for missing it is one of the more expensive per-day costs in the tax code — and it applies even when no tax is owed.

The third estimated tax installment was due September 15. If you missed it, here's how the penalty is actually calculated, what still reduces it, and what doesn't.

Reasonable cause is penalty-specific and fact-specific. A persuasive request explains the event, timeline, ordinary business care and prudence, direct connection to the failure, corrective action, compliance history, and supporting records.

The individual estimated-tax penalty is based on required installments during the year, not merely the balance due with the return. Current-year tax, prior-year tax, adjusted gross income, withholding timing, annualized income, exceptions, and waivers all matter.

Envelope EnvelopeIRS penalties add up fast. A failure-to-file penalty is 5% of the unpaid tax per month, up to 25%. A failure-to-pay penalty is 0.5% per month. On a $20,000 balance, penalties alone can add thousands of dollars to what you owe. But the IRS has formal processes for reducing or removing penalties when the circumstances warrant it. There are two primary paths: first-time penalty abatement (FTA) and reasonable cause. They work differently, have different requireme