Filing taxes in the U.S. can be overwhelming, especially for entrepreneurs, small business owners, and international founders. Between federal obligations with the IRS and separate state requirements, it’s no surprise that many people miss deadlines or don’t file properly. But misunderstanding when and how to file taxes can lead to penalties, missed deductions, and even legal trouble.

At MyUSAService, we specialize in helping business owners—especially international clients—navigate the complexities of U.S. tax compliance. In this post, we’ll break down exactly what’s at stake if you don’t know your tax filing obligations, both federally and at the state level. Whether you’re running a single-member LLC, a multi-member partnership, or a corporation, this guide is here to help you stay compliant and avoid costly mistakes.

The IRS Has Firm Deadlines—Missing Them Means Penalties

One of the most common issues entrepreneurs’ faces is missing federal tax deadlines simply because they didn’t know them. The IRS imposes strict deadlines depending on your business structure:

  • Sole proprietors and single-member LLCs: File using Schedule C and Form 1040 (due April 15).

  • Partnerships and multi-member LLCs: File Form 1065 (due March 15).

  • S corporations: File Form 1120-S (due March 15).

  • C corporations: File Form 1120 (due April 15 or the 15th day of the fourth month after the fiscal year ends).

Failing to file on time can result in a Failure to File Penalty of 5% of unpaid taxes per month, up to 25%. Avoid this by staying ahead of deadlines or filing Form 7004 for an extension.

State Filing Obligations Vary—and Many People Ignore Them

Even if you meet your federal deadlines, each state has its own rules:

  • California: $800 annual franchise tax for LLCs—even with no income.

  • New York: Requires annual filings and minimum income taxes.

  • Texas: No income tax but requires a Franchise Tax Report.

Each state has its own penalties for late or missed filings, so know the rules for every state where your business is active.

International Business Owners Must Understand U.S. Tax Treaties and Reporting Rules

Non-U.S. residents with U.S.-based businesses face additional federal requirements:

  • Form 5472: Required for foreign-owned U.S. LLCs (due April 15 with Form 1120).

  • Form 1120: Required even with no U.S. tax liability.

  • TIN/ITIN Requirements: Needed to file any IRS form.

Failure to file these forms may lead to automatic $25,000 penalties per year. Many international founders mistakenly think they don’t need to file if they had no income—this can be a very costly misunderstanding.

Extensions Are Not Exemptions

Filing an extension gives you more time to file, not more time to pay.

If you don’t pay by the original due date:

  • You’ll face Failure to Pay Penalties (0.5% per month).

  • You’ll accrue interest on unpaid taxes.

  • Penalties and interest compound over time.

Always estimate and pay your expected tax when requesting an extension.

Quarterly Estimated Taxes Are Often Overlooked

If your business earns income and doesn’t withhold taxes, you likely owe quarterly estimated tax payments to the IRS and possibly your state.

Due dates:

  • April 15

  • June 15

  • September 15

  • January 15 (of the following year)

Missing these payments can trigger an Underpayment Penalty, even if you pay in full at year-end. This is common for freelancers, digital entrepreneurs, and foreign LLC owners.

You Might Be Missing Deductions or Overpaying

Filing late—or not at all—often leads to missed deductions that could reduce your tax bill:

  • Business travel and meals

  • Software and subscriptions

  • Marketing and advertising

  • Home office expenses

  • Contractor payments (Form 1099-NEC)

The IRS won’t remind you of what you could have claimed. Keep complete records and file on time to avoid overpaying.

Amended Returns Can Help—but Only If You File in the First Place

If you forgot to file or made a mistake, you can amend using Form 1040-X or a business-specific version. But you can’t amend a return you never filed.

If you skip filing entirely, the IRS may file a Substitute for Return (SFR) on your behalf, which excludes deductions and assumes maximum income—leading to inflated tax bills.

Filing—even late—puts you in a better position to negotiate penalty relief or payment plans.

Conclusion

Understanding how to file taxes with the IRS and states is not optional—it’s essential for running a compliant and successful U.S. business.

At MyUSAService, we offer guidance for international founders, freelancers, and business owners who want peace of mind about tax filing, business compliance, and U.S. growth strategies. Unlocking the key differences between pass-through entities vs. corporations is just one of the ways we help clients choose the right structure and stay compliant. Don’t let confusion turn into costly penalties—reach out to our team and get the clarity you need to succeed.