A great many people file an extension every April, and the six months it buys expire in the middle of October. A good number of the people who took one in April have not touched the return since, on the reasonable theory that October was a long way off.
It is not, any more. The instinct at this point is to start at the beginning: open the shoebox, sort everything by date, and work forward. That instinct is why people are still sorting receipts at eleven at night on the day before. The order below is deliberately different, and it is built around one idea: establish the shape of the return first, then fill it in.
Day one: get access before anything else
Log in to everything you will need, today, before you look at a single receipt. Your IRS online account, your payroll or brokerage portals, last year's return.
Every year a number of people do the entire job and then discover on the final evening that they have lost a login, that an account needs reactivating, or that a form has not arrived. A missing W-2 or 1099 on the last afternoon is a scramble, and no amount of preparation rescues it if you have not checked.
Day two: statements, not receipts
Download the full year of statements for every account the business touched. This is your spine.
Statements are complete in a way that receipts never are. A receipt you lost is invisible; a payment on a statement is not. Working from statements means you start from everything that happened and remove what does not belong, rather than starting from what you happened to keep and hoping it was most of it.
Day three: sort into four piles, roughly
Income. Definitely deductible. Definitely not. Not sure.
Resist precision here. The point is to get the shape, and the shape is nearly always clear within a couple of hours. The fourth pile is the only one that needs thought, and it is usually small, a fraction of the transactions and a fraction of the value.
Most people discover that the agonizing they were dreading applies to perhaps fifteen items, not four hundred.
Day four: total the first three piles and look at the number
You now have a draft figure. It will be slightly wrong and that is fine.
Look at it before you refine anything, because it tells you how much the fourth pile matters. If the not-sure pile could move the tax due by thirty dollars, stop deliberating and take the cautious treatment. If it could move it by two thousand, that is the pile worth a preparer's hour.
Day five: deal with the fourth pile, once
Take each item, make a decision, write one line saying why. The line matters more than the decision does. A defensible reasoning recorded at the time is worth a great deal more than a perfect answer you cannot reconstruct.
Where the amount is material and the treatment genuinely unclear, this is the moment to pay for advice. An hour, with the question already framed and the numbers already totaled, is a cheap hour. The same hour spent on a shoebox is not. It is also the week when every preparer in the country is busy, so call on day one and book it for day five.
Day six: enter it and stop
Fill in the return. Do not file it. Close the laptop.
Day seven: read it cold, then file
Errors that are invisible at midnight are obvious the following morning. A transposed figure, a box left empty, income entered on the wrong line. Twenty minutes with fresh eyes catches nearly all of it. Then file, and save the confirmation somewhere you will find it.
If you are still not going to make it
There is no second extension. The October date is the end of the line for filing, and the penalty for failing to file is considerably steeper than the penalty for failing to pay, which means an incomplete return filed on time beats a perfect one filed in November.
File with your best figures and amend later if something turns out to be wrong. Amending is an ordinary process rather than an admission of anything.
If the problem is that you cannot pay rather than that you cannot file, those are separate issues and the IRS treats them separately. The agency offers installment agreements, and setting one up is far better than filing nothing. What to avoid is the instinct that ties the two together and does neither. Interest and penalties on an unpaid balance have been running since April in any case, so the amount involved does not improve by waiting.
What to do differently next year, in ten minutes
The change that prevents this is not a resolution to be organized, which fails reliably, but two arrangements that run without attention. Open a second business account and put every business payment through it, so the statement is the record. Set a standing transfer moving a fixed share of every payment received into an account you do not touch, so the bill is money you already set aside rather than a number you discover.