October 15 is the final extended return deadline of the tax year, and there is no filing option beyond it. For sole proprietors who reported business income on Schedule C as part of their personal Form 1040, and for C-corporations that filed Form 7004 in April, this is the date by which a completed return must be submitted to the IRS. No additional extension is available.
Eleven weeks from the start of August sounds like comfortable runway. For business owners whose books haven’t been actively maintained since spring, it isn’t. Tax preparers fill their fall schedules quickly, and the clients who arrive with organized, reconciled records receive the most efficient service. The clients who arrive in the final two weeks of October with months of unresolved transactions tend to find that neither the time nor the bandwidth exists to do that work carefully.
August is the preparation window. The work that needs to happen before October 15 belongs in the next few weeks, not in September or October.
Who this deadline applies to
October 15 covers two groups of filers. The first is individual taxpayers, including sole proprietors and single-member LLC owners taxed as sole proprietors, who filed Form 4868 in April to extend their personal return. Their business income flows through Schedule C onto Form 1040, and October 15 is the final filing date for that return.
The second group is C-corporations on a calendar tax year that filed Form 7004 in April to extend their Form 1120. The October 15 deadline applies to both.
This is a separate deadline from September 15, which applies to S-corporations and partnerships that extended their returns in March. Those entity types file earlier because their Schedule K-1s need to reach individual shareholders and partners before those individuals can complete their own returns. Sole proprietors and C-corps operate on their own timeline, and that timeline ends on October 15.
If you are uncertain which deadline applies to your specific business structure, your CPA or tax preparer can confirm it quickly. Getting that answer in August, rather than in late September, leaves time to act on it.
What your April extension actually covered
Filing an extension in April gave you additional time to submit your tax return. It did not give you additional time to pay any taxes owed. Any 2025 tax liability was due by April 15, regardless of the extension. Interest has been accruing on any unpaid balance since that date, compounding daily at the current IRS rate.
This distinction catches business owners off guard more often than it should. An extension is sometimes understood as a broad delay on the tax situation. The payment component did not pause. If there is an outstanding balance on an extended return, calculating and addressing it sooner reduces the total interest owed. Your bookkeeper and your tax preparer need current, accurate financials to make that calculation, which is another reason the state of your records in August matters.
What your tax preparer needs from you
To complete your return, your CPA or tax preparer will need a full view of your business finances for 2025. That means a reconciled profit and loss statement that reflects actual income and expenses for the year, a balance sheet that matches your current account balances, records of any estimated tax payments made during the year, and documentation for significant purchases, equipment, or capital expenditures.
If your books have not been touched since the end of Q1, there is a gap between what your records currently show and where the business actually stands. Every month of unreconciled transactions represents time that needs to be spent before your preparer can begin. Bookkeeping work takes the same amount of time regardless of when it happens. The question is whether it happens in August, when there is room for it, or in October, when there isn’t.
Your preparer may also have specific questions about owner draws or distributions, equity transactions, or particular line items depending on your business structure. The earlier you engage with them, the earlier those questions surface and the more time you have to find the answers.
Why August is the month to close the gap
August occupies a specific position in the tax year. It is the last genuinely quiet month before fall deadlines arrive in sequence. September 15 comes first, bringing the Q3 estimated tax payment for self-employed individuals and the extended return deadline for S-corps and partnerships. Once September is active, attention and capacity across the small business financial world are already spoken for.
Business owners who use August to catch up their records, confirm what their preparer needs, and establish a clear timeline for October are positioned well for a clean close to the tax year. Waiting until September means beginning that work inside a month that is already busy, against a deadline that is now six weeks away rather than eleven.
The gap between where your books are and where they need to be doesn’t close on its own. August is when closing it is still straightforward.
TEVA works alongside your tax preparer
At TEVA Bookkeeping Solutions, we help sole proprietors and C-corp owners get their financial records into shape ahead of October 15. Whether that means catching up several months of bookkeeping or ongoing support through the fall filing season, we work directly with your tax preparer so the numbers they need are accurate and ready on time.