Closing the Books in October: The Q3 Close and Year-End Prep Checklist

The close you run in October is rarely a normal month-end. You're closing September, which is also the end of the third quarter. Some clients have a September 30 fiscal year-end, so for them it's the annual close. And it's the last close with enough runway to fix problems before December 31.

That makes October the best month to find gaps while they're still cheap to fix. Here's what to collect, what to check, and what to start now so January doesn't arrive full of surprises.

1. The September month-end basics

Start with the usual monthly list: bank and credit card statements, payroll registers, sales and payout reports, loan statements, receipts above your threshold, and answers to uncategorized transactions. Our month-end close client document checklist covers each item in detail.

In September, look harder at anything that has been sitting in suspense or “Ask my accountant” since the summer. Items that are three months old now will be nine months old by tax time, and the client will remember them even less.

2. The Q3 quarter-end additions

• Form 941 for the third quarter (due November 2, 2026, because October 31 falls on a Saturday) and state unemployment reports. Tie the payroll provider's quarterly reports to the general ledger before they're filed.
• Quarterly sales tax returns and supporting reports, where the client files them. Many states set their quarterly due dates in October.
• Balance sheet reconciliations, not just bank accounts: loans, credit lines, payroll liabilities, sales tax payable, and owner equity accounts.
• New fixed asset purchases from the quarter: invoices, in-service dates, and any financing documents.
• Inventory counts or valuation reports, where inventory is significant.
• A quick review of year-to-date profit, so the client's fourth-quarter estimated tax payment (due January 15, 2027) isn't a guess.

3. September 30 fiscal year-end clients

Not every client runs on the calendar year. For a business with a September 30 fiscal year, October is the year-end close, and the filing clock is already running. A partnership or S corporation with that fiscal year generally files by December 15; a C corporation by January 15.

For these clients, add the full year-end list now: year-end loan and investment statements, fixed asset details for the whole year, accrued expenses and unpaid bills at September 30, inventory at year-end, owner contributions and distributions, and any legal or ownership changes during the year. Ask early. Their year-end lands in the same weeks your tax team is finishing October 15 extensions.

4. Start year-end prep in October, not January

Most January stress comes from information nobody asked for until it was due. Three things are worth starting this month:

Contractor W-9s and the new $2,000 threshold

For payments made in 2026, the Form 1099-NEC and 1099-MISC reporting threshold rises from $600 to $2,000 per payee. Fewer contractors will need a form, but you still need to know who is over the line, and a missing W-9 is just as painful as it was last year. Pull a year-to-date vendor report now, flag likely 1099 recipients, and request any missing W-9s while the client still has a working relationship with the vendor.

Payroll year-end data

The 2026 Form W-2 adds new Box 12 codes for cash tips (TP) and qualified overtime (TT), plus a tipped occupation code in Box 14b. Clients with tipped staff or overtime should confirm now that their payroll provider is tracking these amounts separately. Fixing it in October means correcting three months of payroll; fixing it in January means correcting twelve.

Year-end planning questions

• Equipment or vehicle purchases planned before December 31.
• Retirement plan decisions that need action before year-end.
• Owner compensation and distributions for S corporation clients.
• Bonuses, new hires, or headcount changes in Q4.
• Anything unusual coming: a sale, a new location, a new entity.

5. Make the October request one list

The common mistake is to send the monthly request, then a quarter-end request, then a year-end planning email, each on a different day. Clients see three asks and answer the easiest one. Send one list per client, grouped into “for September,” “for the quarter,” and “for year-end,” with a due date for each group. Then follow up only on what's missing.

Looking further ahead? Read what to prepare for the 2027 tax season.