If you filed an extension in April, the return is due Thursday, October 15. The payment was due in April — here is what that difference actually costs.
The date
If you filed Form 4868 back in April, your individual return is due Thursday, October 15, 2026. Calendar-year C corporations that extended are on the same date. That is a hard deadline, not a soft one, and there is no second extension to apply for.
Partnerships and S corporations were earlier — their extended returns were due September 15, which has already passed. If that one slipped, the penalty runs per partner or per shareholder, per month, so it is worth dealing with today rather than in October.
The part that catches people: an extension was never an extension to pay
An extension moves the filing date. It does not move the payment date. The IRS is explicit about this — the balance was due in April, and interest and failure-to-pay charges have been accruing since then on anything unpaid.
This surprises people every year, and it usually surprises them in a specific way: they assumed that because they had until October to file, they had until October to pay. If you underpaid in April, the bill in October will be larger than the return says.
The practical consequence is that filing on time still helps even when you cannot pay. The failure-to-file charge is the more expensive of the two by a wide margin. Filing and then arranging payment is almost always cheaper than doing neither.
If your records are not ready
Four weeks is enough time, but only if you start now. In order of what usually holds a return up:
- Bank and credit card statements for the full year, not just the months you remember
- Any 1099s or K-1s that arrived after April and went into a drawer
- Mileage and home office records, which are the ones people reconstruct badly under time pressure
- Anything with a basis question attached — a property sale, an equipment disposal, a business interest that changed hands
What we would do
Send what you have rather than waiting until it is complete. A return that is 80 percent assembled on September 20 finishes comfortably. The same return arriving on October 13 does not, and rushed returns are where errors come from.
If a number is genuinely unknowable by the 15th, that is a conversation worth having in advance — there are better and worse ways to handle it, and the worst one is guessing quietly.
Sources
Every date and requirement above comes from the agency that sets it. Rules change — check the source, or call us.
General information, not tax advice for your situation. Call us at (818) 698-8236 to talk about your own facts.