Business tax deadlines vary by entity type, and the consequences for missing them range from annoying to financially devastating. A sole proprietor who files late faces the same penalties as any individual taxpayer—steep but manageable. But an S-corporation or partnership that misses its March 15 deadline faces penalties calculated per shareholder or partner, per month. A small business with five owners can rack up thousands in penalties in just a few months of delay.
Understanding which deadlines apply to your business—and why they’re structured the way they are—can save you from these costly mistakes. The most important insight: pass-through entities like S-corps and partnerships file a month earlier than C-corps and individuals because they need to provide K-1 forms to owners in time for personal tax returns. Miss this deadline, and you leave your owners unable to file their personal taxes on time.
This guide covers every major business tax deadline for 2026, organized by entity type, plus payroll deadlines, extension rules, and penalty details.
2026 Business Tax Deadline Summary
Before diving into entity-specific details, here’s the high-level picture of when each business type must file:
| Entity Type | 2025 Tax Year Due | Extended Due | K-1/W-2 Due |
|---|---|---|---|
| Sole Proprietor | April 15, 2026 | October 15, 2026 | N/A |
| Single-Member LLC | April 15, 2026 | October 15, 2026 | N/A |
| Partnership | March 15, 2026 | September 15, 2026 | March 15, 2026 |
| Multi-Member LLC | March 15, 2026 | September 15, 2026 | March 15, 2026 |
| S Corporation | March 15, 2026 | September 15, 2026 | March 15, 2026 |
| C Corporation | April 15, 2026 | October 15, 2026 | N/A |
The March 15 vs. April 15 distinction: Notice that pass-through entities (partnerships and S-corps) file a full month earlier than other businesses. This isn’t arbitrary—it’s designed to give owners time to receive their K-1 forms before personal tax returns are due. When a partnership files on March 15, partners receive K-1s showing their share of income, which they then report on their personal April 15 returns.
Sole Proprietor Deadlines
Sole proprietors have the simplest business tax structure—your business income flows directly onto your personal tax return through Schedule C. There’s no separate business return to file and no K-1s to distribute.
2026 Filing Requirements
| Form/Action | Deadline | Notes |
|---|---|---|
| Schedule C (with Form 1040) | April 15, 2026 | Reports business income |
| Schedule SE | April 15, 2026 | Self-employment tax |
| Q1 Estimated Tax | April 15, 2026 | If expecting $1,000+ tax |
| Q2 Estimated Tax | June 15, 2026 | Quarterly payment |
| Q3 Estimated Tax | September 15, 2026 | Quarterly payment |
| Q4 Estimated Tax | January 15, 2027 | Final quarterly payment |
| Extension (Form 4868) | April 15, 2026 | Extends to October 15 |
Key Points
| Item | Details |
|---|---|
| Filing form | Schedule C attached to Form 1040 |
| Self-employment tax | 15.3% on 92.35% of net profit |
| Home office | Form 8829 or simplified method |
| Vehicle | Form 4562 for depreciation |
The self-employment tax reality: Sole proprietors pay both halves of Social Security and Medicare taxes—the employee share and the employer share that would normally be paid by a company. This 15.3% self-employment tax (on the first $168,600 of net earnings in 2026) often exceeds their income tax liability, especially in the first several years of business.
Switching to S-corp status: As a sole proprietor’s income grows, many consider electing S-corp status to reduce self-employment taxes. By paying yourself a reasonable salary (subject to payroll taxes) and taking remaining profits as distributions (not subject to SE tax), you can potentially save thousands annually. The trade-off: more paperwork, payroll compliance, and stricter filing deadlines.
Partnership Deadlines (Form 1065)
Partnerships include traditional partnerships, multi-member LLCs (taxed as partnerships by default), and other entities that have chosen partnership taxation. The March 15 deadline exists specifically to ensure partners receive their K-1 forms in time for personal tax filing.
2026 Filing Requirements
| Form/Action | Deadline | Notes |
|---|---|---|
| Form 1065 | March 15, 2026 | Partnership return |
| Schedule K-1 | March 15, 2026 | To each partner |
| Extension (Form 7004) | March 15, 2026 | Extends to September 15 |
| Extended Filing | September 15, 2026 | With approved extension |
Why March 15?
Partnerships file early so partners receive their K-1s in time to file their personal returns by April 15. This timing is critical because K-1 income must be reported on each partner’s individual return—delaying the partnership return cascades into delayed personal returns for every partner.
K-1 Requirements
| Item | Requirement |
|---|---|
| Deadline to partners | March 15, 2026 |
| Content | Each partner’s share of income, deductions, credits |
| Method | Mail, electronic, or partnership portal |
| Penalty for late K-1 | $290/form (2025 rate) |
The K-1 cascade problem: When partnerships file extensions (which is common), partners don’t receive their K-1s until September 15—forcing every partner to also file personal tax extensions. This cascade effect explains why so many individual taxpayers file extensions even when their own tax situation is straightforward. If you’re waiting on K-1s from partnership investments, you may have no choice but to extend.
Partnership Estimated Taxes
| Requirement | Details |
|---|---|
| Partnership pays | None—pass-through entity |
| Partners pay | Individual estimated taxes on K-1 income |
| Due dates | April 15, June 15, September 15, January 15 |
The partnership estimated tax challenge: Even though partnerships don’t pay entity-level taxes, partners must pay estimated taxes on their expected K-1 income throughout the year. The problem: K-1 amounts aren’t finalized until the partnership return is prepared, often close to the March 15 deadline. This forces partners to estimate their tax liability based on prior-year K-1s or mid-year projections—an inexact science that often results in either overpayment or underpayment penalties.
S Corporation Deadlines (Form 1120-S)
S-corporations combine liability protection with pass-through taxation. Like partnerships, they file on March 15 to allow shareholders time to file personal returns. Unlike partnerships, S-corps must pay reasonable salaries to shareholder-employees, creating additional payroll compliance requirements.
2026 Filing Requirements
| Form/Action | Deadline | Notes |
|---|---|---|
| Form 1120-S | March 15, 2026 | S-corp return |
| Schedule K-1 | March 15, 2026 | To each shareholder |
| Extension (Form 7004) | March 15, 2026 | Extends to September 15 |
| Extended Filing | September 15, 2026 | With approved extension |
| W-2s to employees | January 31, 2026 | Including shareholder-employees |
S-Corp Owner Compensation
| Requirement | Deadline |
|---|---|
| Reasonable salary to owner | Throughout year (payroll) |
| W-2 to shareholder-employee | January 31, 2026 |
| Payroll tax deposits | Per deposit schedule |
| Form 941 (quarterly) | See payroll deadlines below |
The reasonable salary requirement: S-corp shareholder-employees must receive “reasonable compensation” for their services. The IRS watches for shareholders who pay themselves minimal salaries to avoid payroll taxes while taking large distributions. What’s “reasonable” depends on the business, industry, and the shareholder’s role—but significantly underpaying yourself invites IRS scrutiny. Generally, if a similar position in a similar company would command $80,000, paying yourself $30,000 is asking for trouble.
S-Corp Estimated Taxes
| Entity Level | Owner Level |
|---|---|
| S-corp pays $0 (pass-through) | Shareholders pay on K-1 income |
| Built-in gains tax (rare) | Some converted C-corps |
| LIFO recapture (rare) | Inventory situations |
The built-in gains exception: While S-corps generally don’t pay entity-level taxes, corporations that converted from C-corp to S-corp status may owe “built-in gains” tax if they sell appreciated assets within 5 years of the conversion. This tax is at the corporate rate on the gain that existed at the time of conversion. If your S-corp was formerly a C-corp, discuss this with your tax advisor before selling major assets.
C Corporation Deadlines (Form 1120)
C-corporations are separate tax-paying entities, filing their own returns and paying taxes at the corporate level. Unlike pass-through entities, C-corps face “double taxation”—the corporation pays tax on profits, and shareholders pay tax again when profits are distributed as dividends. Despite this, C-corps remain popular for businesses planning to retain significant profits, raise venture capital, or eventually go public.
2026 Filing Requirements (Calendar Year)
| Form/Action | Deadline | Notes |
|---|---|---|
| Form 1120 | April 15, 2026 | Corporate return |
| Extension (Form 7004) | April 15, 2026 | Extends to October 15 |
| Extended Filing | October 15, 2026 | With approved extension |
| Estimated Tax Payments | Quarterly | See schedule below |
Fiscal Year Corporations
| Fiscal Year End | Return Due | Extended Due |
|---|---|---|
| January 31 | May 15 | November 15 |
| June 30 | October 15 | April 15 |
| September 30 | January 15 | July 15 |
| Custom year-end | 15th of 4th month | 15th of 10th month |
The fiscal year advantage: Unlike most other entities that must use a calendar year, C-corps can choose a fiscal year that aligns with their business cycle. A retail business with a fiscal year ending January 31 files its return in May, after the busy holiday season is over and inventory has been counted. This flexibility is a significant advantage for businesses with seasonal patterns.
C-Corp Estimated Tax Payments
| Quarter | Due Date | Based On |
|---|---|---|
| Q1 | April 15, 2026 | 25% of annual tax |
| Q2 | June 15, 2026 | 50% cumulative |
| Q3 | September 15, 2026 | 75% cumulative |
| Q4 | December 15, 2026 | 100% annual tax |
C-corp Q4 timing: Notice that C-corp Q4 estimated taxes are due December 15—a month before individuals’ Q4 deadline of January 15. This catches some business owners by surprise, especially those managing both personal and corporate estimated taxes.
Large Corporation Rule
| Definition | Requirement |
|---|---|
| $1M+ taxable income (prior 3 years) | Must pay 100% of current year tax |
| Cannot use prior year safe harbor | After Q1 payment |
The large corporation trap: Individual taxpayers can avoid underpayment penalties by paying 100% of their prior year tax (the “safe harbor”). Large corporations lose this protection after Q1—they must base estimated payments on the current year’s tax liability starting with Q2. If your corporation had over $1 million in taxable income in any of the prior three years, budget carefully for quarterly payments.
LLC Tax Deadlines
LLCs don’t have their own tax classification—they’re “disregarded” for federal tax purposes and follow the rules for however they’re taxed. This flexibility is a key advantage of the LLC structure, but it also means LLC owners need to understand which deadline applies to them.
LLC Deadline by Tax Election
| LLC Type | Files As | Deadline | Form |
|---|---|---|---|
| Single-member (default) | Sole proprietor | April 15, 2026 | Schedule C (1040) |
| Multi-member (default) | Partnership | March 15, 2026 | Form 1065 |
| Elected S-corp | S corporation | March 15, 2026 | Form 1120-S |
| Elected C-corp | C corporation | April 15, 2026 | Form 1120 |
Single-member LLCs: By default, a single-owner LLC is treated as a “disregarded entity”—the IRS ignores it, and you report business income on Schedule C just like a sole proprietor. You get liability protection from the LLC structure but maintain the simplicity of sole proprietorship taxation.
Multi-member LLCs: When an LLC has two or more members, it’s taxed as a partnership by default. This means March 15 deadlines, K-1 forms, and all the complexity of partnership taxation.
Changing LLC Tax Status
| Election | Form | Deadline |
|---|---|---|
| S-corp election | Form 2553 | March 15 (2 months, 15 days into tax year) |
| Late S-corp election | Form 2553 | With reasonable cause explanation |
| C-corp election | Form 8832 | Within 75 days before or 12 months after |
The S-corp election timing trap: If you want your LLC to be taxed as an S-corp for 2026, you must file Form 2553 by March 15, 2026 (or within 2 months and 15 days of forming the LLC if that’s later). Miss this deadline and you’re stuck with partnership or sole proprietor taxation for the year—unless you can convince the IRS to grant late election relief, which requires demonstrating reasonable cause for the delay.
Payroll Tax Deadlines
Every business with employees (including S-corp shareholder-employees) faces a web of payroll tax deadlines. Missing these can be catastrophic—payroll tax penalties accumulate quickly, and the IRS takes payroll compliance very seriously.
Form 941 (Quarterly Federal Tax Return)
| Quarter | Period Covered | Due Date |
|---|---|---|
| Q1 2026 | January - March | April 30, 2026 |
| Q2 2026 | April - June | July 31, 2026 |
| Q3 2026 | July - September | October 31, 2026 |
| Q4 2026 | October - December | January 31, 2027 |
Annual Payroll Forms
| Form | Purpose | Deadline |
|---|---|---|
| W-2 | Wages to employees | January 31, 2026 |
| W-2 to SSA | Filed with Social Security | January 31, 2026 |
| W-3 | Transmittal summary | January 31, 2026 |
| Form 940 | Annual FUTA return | January 31, 2026 |
| 1099-NEC | Contractor payments ($600+) | January 31, 2026 |
The January 31 crunch: Notice how many payroll forms are due January 31. W-2s to employees, W-2s to the SSA, the annual unemployment return (Form 940), and 1099-NECs for contractors all share this deadline. Businesses should begin preparing these forms in early January to avoid the last-minute scramble.
Payroll Tax Deposit Schedule
| Deposit Schedule | When to Deposit |
|---|---|
| Monthly (< $50,000 lookback) | By 15th of following month |
| Semi-weekly ($50,000+ lookback) | Wed/Fri depending on payday |
| Next-day ($100,000+ in single day) | Next business day |
Lookback Period
| Current Year | Lookback Period |
|---|---|
| 2026 | July 1, 2024 - June 30, 2025 |
| Total employment tax | Determines deposit schedule |
Deposit schedule penalties: The penalty for late payroll tax deposits starts at 2% for deposits 1-5 days late, jumping to 5% at 6-15 days late, then 10% after 15 days. If the IRS sends a notice and you still don’t deposit within 10 days, the penalty reaches 15%. These penalties apply to the deposit amount, not just the late portion—so a $10,000 deposit that’s 10 days late incurs a $500 penalty.
Information Return Deadlines
Beyond tax returns, businesses must file information returns reporting payments made to contractors, interest paid, dividends distributed, and other payments. Missing these deadlines doesn’t affect your tax liability, but it does trigger per-form penalties that add up quickly.
1099 Forms (2025 Tax Year)
| Form | Purpose | To Recipients | To IRS (Paper) | To IRS (E-file) |
|---|---|---|---|---|
| 1099-NEC | Nonemployee compensation | January 31, 2026 | January 31, 2026 | January 31, 2026 |
| 1099-MISC | Rents, royalties, etc. | January 31, 2026 | February 28, 2026 | March 31, 2026 |
| 1099-INT | Interest payments | January 31, 2026 | February 28, 2026 | March 31, 2026 |
| 1099-DIV | Dividend payments | January 31, 2026 | February 28, 2026 | March 31, 2026 |
| 1099-K | Payment card receipts | January 31, 2026 | February 28, 2026 | March 31, 2026 |
When 1099-NEC Is Required
| Situation | Threshold | Form Required |
|---|---|---|
| Payments to contractors | $600+ | 1099-NEC |
| Attorney fees | $600+ | 1099-NEC or 1099-MISC |
| Rent payments | $600+ | 1099-MISC |
| Royalties | $10+ | 1099-MISC |
The 1099-NEC vs. W-2 distinction: One common mistake is misclassifying workers. Employees receive W-2s; independent contractors receive 1099-NECs. The distinction depends on the degree of control you have over how, when, and where the work is performed—not on what you call the relationship. Misclassifying employees as contractors triggers significant back taxes, penalties, and interest.
Extension Rules by Entity
Extensions are automatic for all business types—file the correct form by the deadline, and you get six extra months to complete your return. But “extension to file” is not “extension to pay.” If your business owes tax, interest and penalties still accrue from the original deadline.
Partnership and S-Corp Extensions
| Item | Requirement |
|---|---|
| Form | 7004 |
| File by | March 15, 2026 |
| Extension granted | 6 months (to September 15) |
| Automatic | Yes, if timely filed |
| Payment required | N/A (pass-through—no entity tax) |
Pass-through extension advantage: Since partnerships and S-corps don’t pay entity-level tax (with rare exceptions), there’s typically no tax payment due with the extension. The business simply files Form 7004, and the deadline moves to September 15. However, remember that individual partners and shareholders may need to adjust their personal estimated tax payments if the extended return will show different K-1 amounts than anticipated.
C-Corp Extensions
| Item | Requirement |
|---|---|
| Form | 7004 |
| File by | April 15, 2026 |
| Extension granted | 6 months (to October 15) |
| Automatic | Yes, if timely filed |
| Payment required | Estimated tax still due April 15 |
C-corp extension reality: Unlike pass-throughs, C-corps often owe entity-level tax. The extension gives you more time to file the return, but any tax owed is still due April 15. If you can’t calculate the exact amount, estimate high—it’s better to get a refund than owe interest and penalties. File Form 7004 with a payment covering your estimated tax liability.
Sole Proprietor Extensions
| Item | Requirement |
|---|---|
| Form | 4868 (personal extension) |
| File by | April 15, 2026 |
| Extension granted | 6 months (to October 15) |
| Payment required | Estimated tax still due April 15 |
Sole proprietor extension tip: Form 4868 extends your entire personal return, not just Schedule C. If you’re filing an extension because your business records aren’t ready, remember that you still need to estimate both your business income and any other income for the year. Pay any estimated balance with the extension to avoid underpayment penalties.
Late Filing Penalties
Business tax penalties can escalate alarmingly—especially for pass-through entities where penalties multiply by the number of owners. Understanding the penalty structure helps you prioritize which deadlines absolutely cannot be missed.
S Corporation and Partnership Penalties
| Penalty Type | Amount | Maximum |
|---|---|---|
| Late filing | $235/shareholder or partner/month | 12 months |
| Example: 3-partner LLC, 2 months late | $235 × 3 × 2 = $1,410 | |
| Example: 5-shareholder S-corp, 4 months late | $235 × 5 × 4 = $4,700 |
The multiplier effect: The $235/month penalty (2025 rate, adjusted annually for inflation) applies per partner or shareholder, per month. A partnership with ten partners that files four months late faces $235 × 10 × 4 = $9,400 in penalties—for simply filing late, regardless of whether any tax was owed. This is why extensions are critical for pass-through entities.
First-time abatement: If you have a clean compliance history (no penalties in the prior three years), you may qualify for first-time penalty abatement. The IRS grants this administratively—you just need to ask. It’s worth requesting even for substantial penalties.
C Corporation Penalties
| Penalty Type | Rate | Notes |
|---|---|---|
| Failure to file | 5%/month of unpaid tax | Up to 25% |
| Failure to pay | 0.5%/month of unpaid tax | Up to 25% |
| Combined maximum | 5%/month (first 5 months) | 25% total |
| Minimum penalty | $485 or 100% of tax | If 60+ days late |
The 60-day cliff: If your C-corp return is more than 60 days late, you owe either $485 or 100% of the unpaid tax, whichever is smaller. This minimum penalty applies even if you owe only $200 in tax—you’d owe $200 as the penalty (100% of tax). File within 60 days of the deadline to avoid this cliff.
Information Return Penalties
| Filing Timing | Penalty Per Form | Maximum (Small Business) |
|---|---|---|
| Within 30 days of deadline | $60 | $220,500 |
| 31 days late through August 1 | $120 | $588,500 |
| After August 1 or not filed | $310 | $1,177,500 |
| Intentional disregard | $630 | No maximum |
The volume problem: These per-form penalties seem small until you multiply by volume. A business that issues 100 late 1099s faces $6,000-$31,000 in penalties depending on how late they are. Businesses that use contractors heavily should prioritize W-9 collection and year-end 1099 preparation.
Retirement Plan Deadlines
Retirement plan deadlines involve two distinct considerations: when to set up a plan and when to make contributions. Some plans offer remarkable flexibility, while others have strict deadlines that, once passed, can’t be corrected.
Employer Contribution Deadlines
| Plan Type | For 2025 Tax Year | Notes |
|---|---|---|
| SEP IRA | April 15, 2026 (or extension) | Including October 15 with extension |
| SIMPLE IRA (employer match) | March 1, 2026 | Employer portion |
| 401(k) employer match | Tax filing deadline | Including extensions |
| Solo 401(k) employer | Tax filing deadline | Including extensions |
SEP IRA flexibility: The SEP IRA is unique—you can establish the plan and make contributions up until your tax filing deadline, including extensions. A sole proprietor who files an extension has until October 15, 2026 to both set up a SEP and contribute up to 25% of net self-employment income (up to $69,000 for 2025). This makes SEP IRAs the most flexible last-minute retirement planning tool available.
SIMPLE IRA employer deadline: Unlike SEP IRAs, SIMPLE IRA employer contributions have a hard March 1 deadline—no extensions. If you match employee contributions to a SIMPLE IRA, those matching contributions must be deposited by March 1 following the plan year.
Plan Setup Deadlines
| Plan Type | Setup Deadline |
|---|---|
| SEP IRA | Tax filing deadline (with extensions) |
| SIMPLE IRA | October 1 of current year |
| Solo 401(k) | December 31 of current year |
| 401(k) plan | Before tax year end |
Solo 401(k) timing: A solo 401(k) must be established by December 31 to make contributions for that year. However, if you set up the plan by December 31, you have until your tax filing deadline (including extensions) to actually fund the employer contribution portion. The employee contribution (salary deferral) portion technically must be made by year-end, but for owner-only plans, this deadline is often interpreted more flexibly.
SIMPLE IRA October 1 rule: To establish a new SIMPLE IRA for 2026, you must have the plan in place by October 1, 2026. This deadline exists to give employees time to decide whether to participate. If you’re considering a SIMPLE IRA, don’t wait until year-end—you’ll miss the establishment window.
Business Tax Calendar 2026
Use this month-by-month calendar to track everything due throughout the year. Consider setting calendar reminders 2-4 weeks before each deadline to allow preparation time.
January 2026
January is the most deadline-heavy month for businesses, with W-2s, 1099s, and annual payroll returns all converging on January 31.
| Date | Action |
|---|---|
| January 15 | Q4 2025 estimated taxes (individuals/C-corps) |
| January 31 | W-2s to employees |
| January 31 | 1099-NEC to contractors |
| January 31 | Form 940 (Annual FUTA) |
| January 31 | W-2s/W-3 to SSA |
February 2026
| Date | Action |
|---|---|
| February 28 | 1099-MISC/INT/DIV to IRS (paper) |
March 2026
March is critical for pass-through entities. The March 15 deadline affects partnerships, S-corps, and multi-member LLCs, plus K-1 delivery to owners.
| Date | Action |
|---|---|
| March 1 | SIMPLE IRA employer contributions |
| March 1 | Farmers/fishers return (if didn’t pay estimated) |
| March 15 | Partnership returns (Form 1065) |
| March 15 | S-corp returns (Form 1120-S) |
| March 15 | K-1s to partners/shareholders |
| March 31 | 1099s to IRS (electronic) |
April 2026
April brings the main individual and C-corp filing deadline, plus Q1 estimated taxes for the new year.
| Date | Action |
|---|---|
| April 15 | C-corp returns (Form 1120) |
| April 15 | Sole proprietor returns (Schedule C) |
| April 15 | Q1 2026 estimated taxes |
| April 15 | SEP IRA contributions (without extension) |
| April 30 | Form 941 (Q1 payroll) |
June 2026
| Date | Action |
|---|---|
| June 15 | Q2 2026 estimated taxes |
July 2026
| Date | Action |
|---|---|
| July 31 | Form 941 (Q2 payroll) |
| July 31 | Form 5500 (retirement plan annual return) |
September 2026
September is the extended deadline for pass-through entities filed March 15 extensions.
| Date | Action |
|---|---|
| September 15 | Extended partnership/S-corp returns |
| September 15 | Q3 2026 estimated taxes |
October 2026
October brings extended return deadlines and the final window for some retirement contributions.
| Date | Action |
|---|---|
| October 15 | Extended C-corp and sole proprietor returns |
| October 15 | SEP IRA contributions (with extension) |
| October 31 | Form 941 (Q3 payroll) |
December 2026
December is your last chance for many year-end planning moves and plan establishments.
| Date | Action |
|---|---|
| December 15 | C-corp Q4 estimated taxes |
| December 31 | 401(k) employee contributions |
| December 31 | Business expenses for 2026 deduction |
| December 31 | New solo 401(k) plan establishment |
The Bottom Line
Business tax deadlines are more complex than individual deadlines because entity type determines everything—from which form you file to which deadline applies to how penalties are calculated. The single most important takeaway:
| Entity | Filing Deadline |
|---|---|
| S-corps and partnerships | March 15 |
| C-corps and sole proprietors | April 15 |
| All payroll W-2s/1099s | January 31 |
Why this matters: Missing pass-through deadlines (S-corps, partnerships) is especially costly—penalties accrue per owner per month. A five-partner LLC that files three months late owes $3,525 in penalties regardless of whether any tax was due. A sole proprietor filing three months late owes penalties only on unpaid taxes.
When in doubt, file an extension by the deadline. Extensions are automatic and free; late filing penalties are not. Even if you can’t finalize your return, filing Form 7004 (businesses) or Form 4868 (sole proprietors) by the deadline eliminates the failure-to-file penalty and gives you months more to complete your return properly.
Tax rules change and fiscal year corporations have different deadlines. Consult a tax professional for complex business situations.