Planning ahead for tax season can help business owners avoid missed deadlines, reduce filing stress, and prepare for potential tax liabilities. If you own a small business in Chicago or elsewhere in Illinois, knowing the 2027 business tax filing deadlines is an important step toward keeping your finances organized.
For most calendar-year businesses, tax returns filed in 2027 cover the 2026 tax year. However, the deadline depends on your business structure, the forms you need to file, and whether your business follows a calendar or fiscal tax year.
In this guide, Chicagoland CPAs explains the key federal business tax deadlines for 2027, extension rules, estimated tax payments, and how professional tax preparation can help your business stay on track.
When Are Business Taxes Due in 2027?
The main federal income tax deadlines for many calendar-year businesses are March 15 and April 15, 2027. Partnerships and S corporations generally file earlier than sole proprietors and C corporations.
Here is a quick overview of common federal filing deadlines for the 2026 tax year.
| Business type or filing | General 2027 deadline |
|---|---|
| Partnerships — Form 1065 | March 15, 2027 |
| S corporations — Form 1120-S | March 15, 2027 |
| Sole proprietors — Form 1040 with Schedule C | April 15, 2027 |
| Single-member LLCs taxed as disregarded entities | April 15, 2027, generally with the owner’s individual return |
| C corporations — Form 1120 | April 15, 2027, for calendar-year filers |
| Fourth-quarter 2026 individual estimated tax payment | January 15, 2027 |
| First-quarter 2027 individual estimated tax payment | April 15, 2027 |
These dates apply to common federal filing situations. Other returns, payroll filings, information returns, fiscal-year businesses, and special circumstances may have different deadlines. Confirm your specific requirements with a tax professional and the IRS before filing.
March 15, 2027: Partnership and S Corporation Tax Returns
Partnerships and S corporations using a calendar tax year generally need to file their federal income tax returns by March 15, 2027.
Partnership tax deadline
Partnerships generally file Form 1065 to report business income, deductions, gains, and losses. They also provide Schedule K-1 to each partner so the partner can report their share of the business’s tax items.
Multi-member LLCs taxed as partnerships generally follow the same deadline.
S corporation tax deadline
S corporations generally file Form 1120-S by March 15, 2027. Shareholders receive Schedule K-1 showing their share of the company’s income, deductions, and other tax items.
Preparing these returns early can help owners receive their tax documents on time and coordinate their personal tax filings.
April 15, 2027: Sole Proprietor, Single-Member LLC, and C Corporation Deadlines
April 15, 2027, is an important federal tax date for many businesses and business owners.
Sole proprietors and single-member LLCs
Sole proprietors generally report business income and expenses on Schedule C attached to their individual Form 1040. Single-member LLCs that are taxed as disregarded entities generally report their business activity through the owner’s tax return.
The usual deadline for these calendar-year individual returns is April 15, 2027.
C corporations
Calendar-year C corporations generally file Form 1120 by April 15, 2027. Unlike pass-through entities, C corporations generally pay federal income tax at the corporate level.
Business owners should confirm which return applies to their entity because an LLC’s legal structure alone does not always determine its federal tax treatment.
Quarterly Estimated Tax Payments in 2027
Some business owners must make estimated tax payments throughout the year rather than waiting until their annual return is filed.
Sole proprietors, partners, and S corporation shareholders may need to make individual estimated tax payments. C corporations generally have their own estimated tax payment requirements.
Common 2027 federal estimated tax dates for calendar-year individual taxpayers are:
- April 15, 2027: First payment for 2027.
- June 15, 2027: Second payment for 2027.
- September 15, 2027: Third payment for 2027.
- January 18, 2028: General fourth-payment deadline for 2027, subject to applicable calendar rules.
The fourth payment for the 2026 tax year is generally due January 15, 2027. Estimated tax rules and payment amounts depend on the taxpayer’s circumstances, so business owners should verify their obligations before each due date.
Missing a required estimated payment can result in a penalty even when the annual tax return is filed on time.
Can You Get a Business Tax Filing Extension?
Yes. Eligible businesses can generally request additional time to file certain federal tax returns.
For many calendar-year partnerships and S corporations, Form 7004 can request an extension from March 15 to September 15, 2027. Eligible calendar-year C corporations can generally request an extension from April 15 to October 15, 2027.
Sole proprietors filing individual returns generally request an extension using Form 4868, which typically extends the filing deadline to October 15, 2027.
Important: An extension to file is not an extension to pay. Any tax owed is generally still due by the original payment deadline. You should estimate and pay the amount due on time to help limit interest and penalties.
What Happens If You Miss a Business Tax Deadline?
Missing a filing or payment deadline can lead to penalties, interest, and additional administrative work. The consequences depend on the type of return, how late it is, the amount owed, and the circumstances involved.
To reduce the risk of missed deadlines:
- Maintain organized income and expense records.
- Reconcile business bank and credit card accounts.
- Collect payroll records and contractor information.
- Review deductions and supporting documentation.
- Confirm the correct tax forms and deadlines for your entity.
- Plan for estimated tax payments throughout the year.
- Contact a CPA promptly if you think you may miss a deadline.
Early preparation gives you more time to identify missing records and address questions before filing.
How a Chicago CPA Can Help With Business Tax Preparation
Business tax filing involves more than submitting forms by a deadline. Choosing the correct filing method, reviewing eligible deductions, preparing supporting records, and planning for future tax payments can all affect your business’s financial position.
Chicagoland CPAs helps businesses approach tax preparation and planning with a clearer understanding of their obligations and financial records.
Our business tax services provide more information about available tax services. Working with a CPA can help you organize the filing process, understand relevant deadlines, and plan for tax responsibilities throughout the year.
Whether you operate a sole proprietorship, LLC, partnership, S corporation, or C corporation, the right preparation strategy starts with understanding your business structure and tax obligations.
Prepare for the 2027 Business Tax Season With Confidence
Knowing when business taxes are due in 2027 can help you plan and avoid last-minute filing pressure. Since deadlines and filing requirements vary by entity type, it is important to confirm which rules apply to your business.
Chicagoland CPAs can help you prepare for tax season with professional tax preparation and planning support.
Contact us our team to discuss your business tax needs and take the next step toward an organized filing season.
FAQs About 2027 Business Tax Deadlines
When are business taxes due in 2027?
For many calendar-year businesses filing 2026 federal income tax returns, partnerships and S corporations generally have a March 15, 2027, deadline. Sole proprietors and calendar-year C corporations generally have an April 15, 2027, deadline.
When are LLC taxes due in 2027?
The deadline depends on how the LLC is taxed. A single-member LLC taxed as a disregarded entity generally reports business income on the owner’s individual return, due April 15, 2027. An LLC taxed as a partnership generally files Form 1065 by March 15, 2027. An LLC taxed as a corporation follows the applicable corporate deadline.
Does a tax extension give my business more time to pay?
Generally, no. An extension usually provides more time to file the return, not more time to pay the tax owed. Payment is generally due by the original deadline.
Are Illinois business tax deadlines the same as federal deadlines?
Not necessarily. Illinois state filing and payment requirements can differ from federal requirements and depend on your business and tax situation. Confirm both federal and Illinois obligations before filing.
When should I contact a CPA for 2027 business taxes?
It is best to contact a CPA well before your deadline. Starting early gives you time to organize records, resolve questions, review your filing requirements, and prepare for any tax payments.