Filing an Extension With Real Numbers Behind It
Updated 2026-10
The sentence that matters
An extension gives you more time to file the return. It does not give you more time to pay the tax. Whatever is owed is due on the original date, and from that date interest runs and a late-payment penalty accrues on the unpaid amount. Filing late without an extension adds a separate, larger late-filing penalty on top. So the extension is nearly always worth filing, and it is worth filing with a payment that is close to right.
Why "close to right" needs the bank
An extension payment is an estimate of the year’s tax. Estimated from memory, it is usually low, because people remember sales and forget expenses or the other way round. Estimated from the bank, it is defensible: income and expenses totalled from statements, even before the coding is finished, give a figure your preparer can use. That is what a bookkeeper produces in the days before a deadline when the full catch-up cannot be finished in time.
The dates, again
S corporations and partnerships: March 15, extended to September 15. Sole proprietors, single-member LLCs and C corporations: April 15, extended to October 15. States vary. The S-corporation late-filing penalty is per shareholder per month, which is why that extension in particular is cheap insurance.
What happens after the extension is filed
The pressure comes off, and the order of work stays the same: the current year is reconciled first and handed to the preparer as soon as it closes; older years follow. The extended date is a real deadline, not a suggestion, and your bookkeeper’s quote includes a timeline that lands the package well before it. Estimated payments for the current year are set from the finished figures so next April is not a repeat.
Filing a return with rough numbers instead
Some people would rather file something on time than extend. A return that will need amending costs the preparer’s fee twice and can draw attention; an extension with a good estimate costs little. Which is right in your case is your preparer’s call, and it is a better conversation when the estimate exists.
Where to go next
- Behind on bookkeeping before a tax deadline
- What your tax preparer needs, and by when
- Catch-up bookkeeping services
Common questions
If I file an extension do I still owe penalties?
Interest and a late-payment penalty on any unpaid balance from the original date, yes. The larger late-filing penalty is avoided. Your preparer confirms the specifics.
Can my bookkeeper file the extension?
The preparer files it. Your bookkeeper produces the estimate it is based on.
What if I cannot pay what is owed?
File the extension anyway, with whatever can be paid. Payment arrangements are a conversation with your preparer and the IRS; not filing makes every option worse.