The Solo Attorney Practice Tax Calendar: Every Deadline You Cannot Miss

2026-08-21

A practical guide to tax deadlines for solo attorneys, covering quarterly estimates, annual filings, and key dates to avoid penalties.

Running a solo law practice means you are the CEO, the CFO, and the tax department. Missing a tax deadline can trigger penalties, interest, and unnecessary stress. This guide lays out every critical tax date for 2026, with concrete steps to stay compliant and save money.

Quarterly Estimated Tax Deadlines

The IRS expects you to pay taxes on income as you earn it. For a solo attorney, that means making quarterly estimated tax payments. If you owe more than $1,000 at filing time, you may face an underpayment penalty. The 2026 deadlines are:

April 15, 2026: Covers income from January 1 through March 31.
June 15, 2026: Covers income from April 1 through May 31.
September 15, 2026: Covers income from June 1 through August 31.
January 15, 2027: Covers income from September 1 through December 31.

How to calculate: Use IRS Form 1040-ES. A simple method is to pay 100% of your previous year’s tax liability (or 110% if your adjusted gross income was over $150,000). Alternatively, pay 90% of your current year’s liability. Many solo attorneys use the safe harbor method to avoid penalties.

Practical step: Set aside 30% to 35% of every client payment into a separate tax savings account. This covers federal income tax, self-employment tax, and state taxes. Review your profit and loss statement monthly to adjust your estimated payments.

Annual Filing Deadlines

Beyond quarterly payments, you must file annual returns. The key dates for 2026 are:

March 15, 2026: If your practice is an S-corp or partnership, file Form 1120-S or Form 1065. You also need to issue Schedule K-1s to shareholders or partners.
April 15, 2026: Sole proprietors and single-member LLCs file Schedule C with your personal return (Form 1040). This is also the deadline for C-corps (Form 1120).
October 15, 2026: Extended deadline for individual returns if you filed Form 4868 by April 15. Note: an extension to file is not an extension to pay. Interest and penalties accrue on unpaid taxes from April 15.

State taxes: Most states follow the federal deadlines, but check your state’s tax authority. Some states require separate estimated payments and have different due dates. For example, California requires an additional payment on January 15, and its filing deadline is usually April 15, but confirm on the FTB website.

Practical step: Mark these dates in your calendar now. Set reminders two weeks before each deadline to gather documents and review your numbers.

Payroll Tax Deadlines (If You Have Employees)

If you hire staff, you must handle payroll taxes. The IRS requires deposits on a monthly or semiweekly schedule, depending on your total tax liability.

Monthly depositor: If your payroll tax liability is $50,000 or less in the prior lookback period, deposit by the 15th of the following month.
Semiweekly depositor: If your liability exceeded $50,000, deposit within 3 banking days after the payday.

Forms: File Form 941 quarterly (due April 30, July 31, October 31, and January 31). Also file Form 940 annually by January 31 for federal unemployment tax.

Practical step: Use a payroll service like Gusto or ADP. They automate deposits and filings, reducing the risk of missed deadlines. Costs range from $40 to $100 per month, plus a base fee.

Retirement Plan Deadlines

Solo attorneys can use retirement plans to reduce taxable income. Deadlines vary by plan type:

SEP IRA: You can set up and contribute up to the tax filing deadline, including extensions (April 15, 2026, or October 15, 2026 if extended). The contribution limit for 2026 is $70,000, or 25% of compensation, whichever is less.
Solo 401(k): You must establish the plan by December 31, 2025, to make contributions for 2025. Employee deferrals are due by December 31, 2025, but employer contributions can be made by the filing deadline.
Defined Benefit Plan: More complex, but allows larger contributions. Setup must be done before year-end.

Practical step: If you don’t have a retirement plan, talk to a financial advisor or CPA this month. A SEP IRA is the simplest to set up and can be done after year-end.

State and Local Taxes

Beyond income taxes, solo attorneys may owe:

Sales tax: If you sell legal forms or products, you may need to collect sales tax. Check your state’s rules. Deadlines vary, often monthly or quarterly.
Franchise tax: Some states impose a franchise tax on LLCs or corporations. For example, California charges an $800 minimum franchise tax, due by April 15.
Property tax: If you own your office, property taxes are due per your county’s schedule.

Practical step: List all state and local tax obligations on a spreadsheet, with due dates and amounts. Review it quarterly.

Tax Deduction Deadlines and Strategies

To lower your tax bill, take advantage of deductions before year-end. Key deductions for solo attorneys:

Home office: If you use a space exclusively for your practice, you can deduct $5 per square foot, up to 300 square feet (max $1,500) using the simplified method.
Equipment and software: Under Section 179, you can deduct the full cost of qualifying equipment, like computers and legal research software, in the year you place it in service.
Continuing legal education (CLE): Deduct registration fees, travel, and lodging for CLE courses.
Health insurance premiums: Deduct premiums for you and your family, as long as you are not eligible for employer-sponsored coverage.

Practical step: Before December 31, 2026, review your expenses. If you need new equipment, buy it before year-end to claim the deduction. Keep receipts and a mileage log if you use your car for client meetings.

FAQ

Q: What happens if I miss a quarterly estimated tax payment? A: You may face an underpayment penalty, which is calculated based on the amount you owe and the time it was unpaid. The IRS interest rate for underpayments in 2026 is around 8%, compounded daily. You can reduce the penalty by paying as soon as possible.

Q: Can I pay my taxes with a credit card? A: Yes, the IRS accepts credit card payments through third-party processors. However, they charge a convenience fee of about 1.85% to 2.9% of the payment amount. Weigh the fee against any rewards or cash flow benefits.

Q: Do I need to file a separate tax return for my LLC? A: If you are a single-member LLC, you do not file a separate federal return. You report income on Schedule C of your personal Form 1040. For state purposes, some states require a separate return or franchise tax filing.

Q: What should I do if I can’t pay my taxes in full? A: File your return on time and pay as much as you can. The IRS offers installment agreements, which allow you to pay over time. The setup fee ranges from $31 to $225, depending on your income and payment method. Interest and penalties still apply.

The Bottom Line

Missing a tax deadline can cost you money and peace of mind. The key dates for 2026 are April 15, June 15, September 15, and January 15 for estimates, plus March 15 and April 15 for annual filings. Set up a system now: use a dedicated tax savings account, automate payroll if you have staff, and review your deductions quarterly. If you are unsure about any deadline, consult a CPA who works with solo attorneys. A few hours of planning can save you thousands in penalties and interest.