Startup Tax Deadlines: A Complete Calendar for Founders

Missing tax deadlines can result in significant penalties and interest charges. For startups, these penalties can be particularly painful given the limited cash resources. Beyond the financial cost, missed deadlines can create complications during fundraising when investors conduct due diligence on your tax compliance.

The good news is that most tax deadlines are predictable and can be planned for. This guide covers all the key deadlines startup founders need to track throughout the year.

January is a critical month with multiple deadlines. January 15th is the fourth quarter estimated tax payment due for the prior year. January 31st is the deadline for filing W-2 forms with the IRS, filing Form 1099-NEC for contractors, and filing Form 940 for federal unemployment tax. This is also when you should begin gathering documents for the prior year's tax return.

March 1st is the Delaware franchise tax deadline—a commonly missed deadline that results in $200+ late fees. This is unique to Delaware corporations and differs from other tax deadlines.

April 15th is the federal income tax return due date (or October 15th with extension) and the first quarter estimated tax payment due for the current year. This is the main deadline for filing your corporate tax return.

In addition to annual deadlines, startups must make quarterly estimated tax payments. These payments are due on April 15th, June 15th, September 15th, and January 15th.

Estimated tax payments cover both federal income tax and self-employment tax (for founders paying themselves a salary). The goal is to pay enough throughout the year to cover your tax liability and avoid underpayment penalties.

As a startup, you may not owe income tax if you're still in a loss position, but you likely owe self-employment tax if you're paying yourself a reasonable salary through a payroll system.

Payroll taxes have their own separate deadlines. Federal payroll taxes include Social Security (employer matches employee 6.2% up to wage base), Medicare (employer matches employee 1.45% with no cap), and Federal Unemployment (employer pays 6.0% on first $7,000 of wages).

Form 941 (federal payroll tax return) is due quarterly, within one month after the end of each quarter. Form 940 (annual federal unemployment tax) is due January 31st.

Most startups are required to deposit payroll taxes monthly or even semi-weekly, depending on your tax liability. Your payroll provider can help you understand your deposit schedule.

Delaware franchise tax is due March 1st annually. This is for Delaware C-Corporations only and is separate from federal tax deadlines.

The franchise tax is calculated based on either the number of authorized shares or the assumed par value of your company's assets. You can choose whichever method results in a lower tax. The minimum tax is $400, but it can be significantly higher depending on your company's valuation.

Late payment incurs a $200 penalty plus 1.5% monthly interest on unpaid tax. Many startups miss this deadline because it differs from federal tax deadlines.

If you've granted stock options, there are additional deadlines to track. Employees who exercise options may have tax obligations at exercise time. If you've filed 83(b) elections for founder equity, those must be filed within 30 days of receiving the equity.

For companies with equity compensation, you'll need to file Form 3921 (for ISOs) or Form 3922 (for NSOs) to report option exercises to the IRS and employees.

The best way to stay on top of tax deadlines is to set up a system. We recommend using a shared calendar (Google Calendar, Outlook, etc.) with reminders at least one week before each deadline. Many startups also use accounting software or connect with a fractional CFO who can manage this for you.

Setting aside money for tax payments throughout the year is equally important. Many founders are surprised by their tax bills because they haven't been setting aside enough. A good rule of thumb is to set aside 25-30% of any profits or owner distributions for taxes.