The tax deadline you didn't know you had is the expensive one

Quick answer: The tax you owe rarely sinks a small business. A missed date does. Put every federal and state filing on one calendar this week, open a separate account for tax money, and book an hour with a CPA to check the list.

April 15 is a myth

Picture a landscaper who's been in business six years. He files his personal return every April, on time, and he's proud of it. Then in March he gets a notice. His company is an S corporation, and its return was due March 15. Nobody mentioned it. The penalty is charged per owner, per month, and it keeps running while he figures out what happened.

That story repeats itself every year in some form. The deadline you know about gets handled. The one you don't becomes a letter.

Partnerships and S corporations generally file a month ahead of individuals. If you're one of them, your business return is due March 15 and your personal one follows. An extension on the business return is easy to get (Form 7004), but it only extends the time to file. It doesn't extend the time to pay.

Estimated taxes, the quarterly surprise

Work for yourself and nobody withholds anything. The IRS still expects to be paid as you go. That means estimated payments four times a year, around April 15, June 15, September 15 and January 15.

The dates are uneven, which is why people miss them. The June payment lands only two months after the April one. The September one lands in the same stretch as everything else going wrong that month.

Miss them or pay too little and you owe an underpayment penalty, even if you pay the whole balance in full at filing. There's a safe harbor that most owners should ask about: paying at least as much as last year's total tax, or a higher percentage if your income was high, generally keeps the penalty away even if this year comes in bigger. Your CPA can tell you which version applies to you. A good year shouldn't be punished by the rule that was supposed to protect you.

Add self-employment tax and the surprise gets bigger. That's the Social Security and Medicare you'd normally split with an employer, and as the owner you carry both halves. The rate is 15.3 percent on net earnings up to the Social Security wage base, and it's separate from income tax. First-year owners often budget for income tax and forget this one entirely.

Payroll taxes will chase you personally

If you have even one employee, you're holding money that was never yours. The income tax and the employee's share of Social Security and Medicare come out of their paycheck. You owe it to the government on a deposit schedule that depends on your size, and you report it quarterly on Form 941.

Spending that cash on a bad month is the worst mistake in this whole article. Withheld payroll taxes are called trust fund taxes for a reason. If they aren't paid, the IRS can assess the Trust Fund Recovery Penalty against the people responsible for paying them, and that means you personally. It doesn't matter that the company is an LLC or a corporation. The structure protects you from a lot, but not from this.

Treat payroll tax like a bill that's already paid. Pay it when the paychecks go out, before rent, before the supplier you're nervous about. If you're about to bring on your first person, read what to file before your first employee starts first.

January is paperwork month

Four things pile up at the end of January:

• W-2s to employees and the Social Security Administration
• 1099-NEC forms to contractors you paid, and copies to the IRS
• Form 940, the annual federal unemployment tax return
• The fourth-quarter Form 941

The 1099 trips up more owners than anything else here, and the fix is boring. Get a W-9 from every contractor before you pay them the first time. Not in January, when the guy has moved and stopped answering his phone. A contractor who won't give you a W-9 can trigger backup withholding, which is its own headache.

The dollar threshold that requires a 1099-NEC has been $600 and is set to change for payments made starting in 2026. Check the current figure with the IRS or your accountant instead of trusting anybody's memory, including mine.

And know that calling someone a contractor doesn't make him one. If you control when, where and how he works, the IRS and your state may see an employee. Misclassification brings back payroll taxes, penalties and interest. Ask a CPA or an employment attorney before you lean on the label.

The state and local filings nobody mentions

Federal gets the attention. State and local is where the quiet surprises live.

Sales tax. In 2018 the Supreme Court decided South Dakota v. Wayfair, and states have been collecting from out-of-state sellers ever since. Many states now set a threshold, often in the neighborhood of $100,000 in sales into the state, past which you have to register and collect. Sell online or ship to other states and you can cross a line in a state you've never visited. Check each state's rule. Don't guess.

Annual reports and franchise taxes. Most states want a yearly report from your entity, and some charge a fee or a franchise tax with it. Miss it and the state can move your company out of good standing. That can freeze your ability to do business, and it tends to show up when a bank or buyer asks for a certificate.

Business personal property tax. A lot of counties tax your equipment, and they want a yearly list of it. The notice often goes to an address you stopped checking.

State unemployment tax. Hire anyone and you'll probably need a separate state account and rate. It's easy to register the federal side and forget the state.

Heavy trucks. If you run vehicles at 55,000 pounds gross weight or more, there's an annual federal highway use tax on Form 2290. It's a narrow rule, and the people it hits usually learn about it from a roadside inspection.

Build the calendar in one sitting

Take an hour. Write every federal, state and local filing on a single calendar with the date, the form, and who's responsible. Put a reminder two weeks ahead of each, not the day before. Deadlines don't get easier to meet at the last minute.

Then fix the money side. Open a separate savings account just for taxes. Every time a customer pays you, move a fixed slice into it before you touch the rest. Ask your CPA what slice to use for your situation, because it depends on your entity and income. Late customers make this harder, and if that's your issue, most late invoices are a process problem, not a people problem. Fix that and the tax account fills on time.

Last, pay a CPA to read your list. Software handles the math fine. What it won't do is tell you about a state registration you never knew existed. A CPA who knows your industry and state can do that in an hour, and the fee is a fraction of one late-filing penalty. Pair it with a monthly look at your own numbers, which ten minutes with your profit and loss covers.

Nobody enjoys the paperwork. It's a toll you pay for the privilege of building something, and the toll booth doesn't care whether you saw the sign. Put the dates on the wall and make them boring. Boring is how you keep the money you earned.