The New Advisory Firm Tax Calendar: Every Deadline You Cannot Miss

Running a new advisory firm means juggling client portfolios, business development, and a growing list of regulatory requirements. Taxes are a critical piece, and missing a deadline can trigger penalties, interest, and unnecessary stress. This guide lays out the key federal and state tax deadlines for 2026, tailored to the typical advisory firm structure (LLC, S-corp, or C-corp). You will know exactly what to file, when to file it, and what to do this week to stay ahead.

Q1 Deadlines: January 15 to March 15

January 15: Estimated Tax Payment (Q4 2025)

If your firm is a sole proprietorship, partnership, or S-corp, you must pay your fourth quarter 2025 estimated tax by January 15, 2026. Use Form 1040-ES for individuals or Form 1120-W for corporations. The penalty for underpayment is roughly 7% annualized on the shortfall, so do not skip this.

January 31: Forms W-2 and 1099-NEC

Send W-2s to employees and 1099-NECs to independent contractors who earned $600 or more in 2025. File copies with the IRS by January 31. E-filing is mandatory if you file 10 or more returns. Late filing penalties start at $60 per form, up to $630,000 for large firms.

February 28: 1099-NEC Paper Filing Deadline

If you are filing paper 1099-NECs, the deadline is February 28. E-filers get an extra month (March 31). Paper filers also need to submit Form 1096, the summary transmittal.

March 15: Partnership and S-Corp Tax Returns

File Form 1065 (partnership) or Form 1120-S (S-corp) by March 15. This is also the deadline for Schedule K-1s to partners and shareholders. If you need more time, file Form 7004 by March 15 to get a six-month extension, but note that extensions do not extend tax payments.

Q2 Deadlines: April 15 to June 15

April 15: Individual and C-Corp Returns

For sole proprietors and single-member LLCs, file Form 1040 by April 15. C-corps file Form 1120 by April 15. Also, make your first quarter 2026 estimated tax payment by April 15. If you cannot file, submit Form 4868 for an automatic six-month extension, but pay any tax due to avoid interest and penalties.

April 15: IRA and HSA Contributions

Contributions to traditional IRAs and HSAs for 2025 must be made by April 15, 2026. The IRA limit is $7,000 ($8,000 if age 50+), and the HSA limit is $4,300 for self-only or $8,550 for family coverage (2026 figures).

June 15: Second Quarter Estimated Tax

Pay your second quarter 2026 estimated tax by June 15. If you are a U.S. citizen living abroad, this is also the deadline for your 2025 tax return (automatic extension to June 15).

Q3 Deadlines: September 15 to October 15

September 15: Third Quarter Estimated Tax and Extended Partnership/S-Corp Returns

Pay your third quarter 2026 estimated tax by September 15. Also, if you filed Form 7004 in March, this is the final deadline for your 2025 partnership or S-corp return.

October 15: Extended Individual and C-Corp Returns

If you filed Form 4868 in April, your 2025 Form 1040 or Form 1120 is due by October 15. This is also the deadline for extended C-corp returns.

Q4 Deadlines: December 15 and Year-End Planning

December 15: Extended C-Corp Returns

If you filed an extension for a C-corp, the final deadline is December 15. After this, you cannot file an extension for the prior year.

December 31: Last Day for Retirement Contributions

To deduct contributions to SEP IRAs or solo 401(k)s for 2026, they must be made by December 31. The SEP contribution limit is 25% of compensation, up to $69,000 (2026). For solo 401(k)s, the employee deferral limit is $23,500, plus a catch-up of $7,500 if age 50+.

Year-End Planning: Defer Income, Accelerate Expenses

Before December 31, review your cash basis books. Defer invoicing to January if possible, and prepay deductible expenses like rent, software subscriptions, and professional fees. This shifts taxable income to 2027.

Payroll Tax Deadlines: Monthly or Semiweekly

Payroll taxes (federal income tax, Social Security, Medicare, and FUTA) have their own schedule. Most small firms deposit monthly, meaning the deposit for wages paid in a month is due by the 15th of the following month. If your firm has more than $50,000 in payroll tax liability in a lookback period, you must use the semiweekly schedule, which requires deposits within 3 banking days after payday. Always check the IRS Publication 15 for exact rules.

Form 941: Quarterly Payroll Returns

File Form 941 by the last day of the month after each quarter: April 30, July 31, October 31, and January 31. This reports wages and taxes withheld. If you use a payroll service, they handle this, but you are still responsible for accuracy.

Form 940: Annual Federal Unemployment Tax

File Form 940 by January 31, 2027, for 2026. The FUTA tax rate is 6% on the first $7,000 of each employee’s wages, but you get a credit of 5.4% if you pay state unemployment taxes, netting 0.6%.

State and Local Deadlines: Vary Widely

State income tax deadlines often mirror federal dates, but not always. For example, California requires S-corp returns by March 15, but the state’s franchise tax is due April 15. New York has a separate estimated tax schedule. Check your state’s department of revenue website for a specific calendar. Also, many cities impose a gross receipts tax, like New York City’s General Corporation Tax, which has its own due dates.

Practical Steps to Take This Week

1. Set up a tax calendar: Use a tool like Google Calendar or a dedicated tax software. Add all deadlines from this guide, plus your state’s dates.
2. Open a separate bank account for taxes: Transfer 25% to 30% of every client fee into this account. This covers income tax and self-employment tax.
3. Review your entity structure: If you are a sole proprietor, consider electing S-corp status before March 15 to save on self-employment taxes. Consult a CPA.
4. Hire a tax professional: A CPA with advisory firm clients can save you thousands. Fees range from $1,500 to $5,000 annually for preparation and planning.
5. Use accounting software: QuickBooks or Xero can automate estimated tax calculations and reminders.

FAQ

What happens if I miss a deadline?

The IRS charges a failure-to-file penalty of 5% of the unpaid tax per month, up to 25%, plus interest. Failure-to-pay is 0.5% per month. State penalties vary, often 5% per month as well.

Can I get an extension on tax payments?

Extensions only extend the filing deadline, not the payment deadline. You must estimate and pay any tax due by the original deadline to avoid penalties.

Do I need to make estimated tax payments in my first year?

Yes, if you expect to owe $1,000 or more in tax. The safe harbor rule: pay 100% of last year’s tax (or 110% if AGI over $150,000) to avoid underpayment penalties.

How do I handle taxes for independent contractors I hire?

You do not withhold taxes for 1099 contractors. You must issue a 1099-NEC by January 31 and file with the IRS. You also need a W-9 from each contractor before paying them.

Related guides

• 7 Questions to Ask Before Buying a New Advisory Firm
• 7 Things to Know Before You Start a New Advisory Firm
• Best New Advisory Firm Tools Compared in 2026

The bottom line

A new advisory firm faces a steep learning curve, but tax deadlines are non-negotiable. Mark the key dates from this guide, set up a dedicated tax account, and work with a CPA to stay compliant. The cost of missing a deadline is far higher than the cost of a good accountant. Start this week by setting up your tax calendar and reviewing your entity structure. Your future self will thank you.