December is light on actual filing deadlines for a venture-backed startup. There is one federal payment date. What December really decides is how painful January, February and March will be. Almost every early 2027 deadline, from W-2s to the Delaware franchise tax, depends on work that is easiest to do before the year closes.
Here are the December startup tax deadlines for 2026 and the year-end checklist we run with clients. For the full year ahead, see the 2027 startup tax deadlines calendar.
The December 15 Corporate Estimate
Tuesday, December 15, 2026: Q4 2026 corporate estimated tax. For a calendar-year C-corp this is the fourth and final 2026 installment. Corporate estimates fall on the 15th day of the 4th, 6th, 9th and 12th months of the tax year, which is why there is no corporate payment in January. January 15 belongs to founders paying personal estimates on Form 1040-ES.
You generally owe estimates if you expect $500 or more of federal tax for the year. Many startups owe nothing because they are losing money, but check before assuming. A year with real revenue, interest income on a large post-raise cash balance, or a change in how research costs are deducted can produce taxable income.
Underpayments are computed on Form 2220 and charged at the IRS underpayment rate, which is 7 percent for the fourth quarter of 2026. Large corporations, those with taxable income of $1 million or more in any of the prior three years, cannot rely on last year's tax as a safe harbor except for the first installment, so they need a real current-year projection.
Year-End Payroll and W-2 Prep
W-2s for 2026 are due to employees and the Social Security Administration on February 1, 2027, because January 31 is a Sunday. The filing itself is automated by most payroll providers. The data is not. Before your final December payroll:
- Confirm every person who should be on payroll is on payroll. Founders who took no salary for part of the year, then started, are a common source of corrections.
- Reconcile taxable fringe benefits. Personal use of a company card, gym stipends and certain gift cards need to be in wages before the last payroll.
- Check state registrations. Every state where an employee worked during 2026 needs withholding and unemployment accounts. A remote hire who moved mid-year can create a new state.
- Review new 2026 reporting items. The 2025 tax law added reporting for items such as tips and overtime. Ask your payroll provider how it is handling these on 2026 forms.
Collect W-9s Before 1099 Season
The 1099-NEC is also due February 1, 2027, to both contractors and the IRS. The rules for 2026 payments are different from every prior year: under the One Big Beautiful Bill Act, the threshold for reporting nonemployee compensation rose from $600 to $2,000 for payments made after December 31, 2025. The IRS 1099 instructions confirm the change and note that the figure may be indexed for inflation starting in calendar year 2027.
What this means in practice:
- Pull a 2026 vendor payment report now and flag every US person or non-corporate entity paid $2,000 or more by check, ACH or wire.
- Exclude card and payment app payments. Those are reported by the processor on Form 1099-K.
- Remember the exceptions. Attorney gross proceeds are still reportable at $600, and royalties at $10.
- Collect W-9s from everyone likely to cross $2,000 by year-end, not only those who already have. The same $2,000 level now governs backup withholding, so a missing taxpayer ID matters once a payee crosses it.
December is the right time because contractors answer email before the holidays. In late January they do not. Late or missing 1099s due in 2027 cost $60 to $340 per form, and $690 per form for intentional disregard.
Year-End Accrual Cleanup for the Close
Your December close feeds your Form 1120, your Delaware gross assets figure and your R&D credit. Before the year ends, line up:
- Unbilled and unpaid expenses. Accrue December legal, contractor and cloud bills that will arrive in January.
- Deferred revenue. Annual contracts billed upfront need a clean deferred revenue schedule, both for GAAP and for how revenue is recognized for tax.
- Prepaid expenses. Annual software, insurance and conference spend should be on the balance sheet and amortized.
- Fixed assets and capitalized software. Laptops, equipment and internal-use software need a schedule.
- Equity transactions. SAFEs, priced rounds, option exercises and 83(b) elections from 2026 should match the cap table.
If month-end has been loose all year, read our guide to the month-end close for startups and fix the process before the year-end close, not during it.
Refresh Your 409A Before New Grants
Many startups batch option grants in January. If yours does, check your 409A now. A valuation supports safe harbor for up to 12 months, and a priced round, a significant revenue change or an acquisition offer can make it stale sooner. Grants priced on an outdated valuation lose that protection, and the tax consequences land on employees. Ordering in December means the report is ready for a January board consent. See what a 409A valuation is for the details.
Delaware Franchise Tax Prep for March 1
The Delaware annual report and franchise tax are due Monday, March 1, 2027. Under the authorized shares method the minimum tax is $175, and under the assumed par value capital method the minimum is $400, plus a $50 annual report fee. For startups with millions of authorized shares, the authorized shares method can produce a bill in the tens of thousands, while the assumed par value capital method usually lands near the minimum.
The cheaper method needs two figures as of December 31, 2026: total gross assets and issued shares. Make sure your cap table reflects every 2026 issuance, and plan to have the balance sheet closed by early February. Our Delaware franchise tax calculator runs both methods.
R&D Credit Documentation for 2026
The research credit for 2026 will be claimed on Form 6765 with the 2026 return, due April 15, 2027 or October 15, 2027 on extension. The documentation is much easier to build while 2026 is still fresh:
- Project list. Name each product or technical project worked on in 2026 and the technical uncertainty it addressed.
- People and time. Map engineers, product staff and contractors to projects, with a reasonable time allocation.
- Contractor agreements. US contract research generally qualifies at 65 percent of cost, but only if you retain rights and bear the financial risk.
- Supplies and cloud costs. Identify development and testing spend separately from production hosting.
This matters more for 2026 than prior years. The IRS made the business component detail in Section G of Form 6765 optional for tax years beginning before 2026; for 2026 and later it becomes required for many filers, with exceptions for smaller ones. If you are a qualified small business planning the payroll tax election, the return must be timely filed, including extensions, or the election is lost. Our R&D tax credit estimator gives a first-pass number.
January 2027 Dates Coming Up
- Friday, January 15, 2027: Q4 2026 personal estimated tax (Form 1040-ES) for founders with non-wage income.
- Monday, February 1, 2027: W-2s, 1099-NEC (recipient and IRS copies), Form 941 for Q4 2026 and Form 940. January 31 is a Sunday, so everything shifts.
- Tuesday, February 16, 2027: recipient copies of 1099-MISC for box 8 and box 10 payments. February 15 is Washington's Birthday.
- Monday, March 1, 2027: Delaware franchise tax and annual report, and paper 1099-MISC filings.
How We Help
At StartupCFO, deadline tracking across all 50 states comes with every plan, and every plan includes a 50 percent discount on preparation of one federal and one state return, with filing fees and additional states as add-ons. Whether you work with us or not, the year-end checklist above is the difference between a calm January and a scramble.
