Choice of entity is the first tax decision a business makes and the one hardest to unwind later. It's also not a single decision. It's a chain of them: the legal form, the tax classification (which can differ), the elections that lock the classification in, and the state where it all lives. Each link has its own filing, and several have deadlines that don't forgive.
The choice-of-entity math
The real comparison isn't LLC versus corporation. It's how each candidate is taxed: partnership pass-through with its flexibility and self-employment tax questions, S corporation pass-through with its salary-and-distribution mechanics and eligibility limits, or C corporation treatment with entity-level tax, potential double taxation, and access to benefits like §1202's qualified small business stock exclusion for eligible C corporation shareholders. The right answer turns on the owners, the exit plans, the loss expectations, and the states involved, which is why it deserves a worked analysis per client rather than a default.
Check-the-box: classification is elective
Under the entity classification regulations, most domestic unincorporated entities get a default (a multi-member LLC defaults to partnership treatment, a single-member LLC is disregarded) and can elect otherwise on Form 8832. The classification election is powerful and sticky: it binds for years, and changing it has tax consequences of its own. The recurring questions are about defaults for foreign entities, the effective-date rules, and what a change in classification is deemed to be for tax purposes.
The S election and its deadline
S corporation status requires an election on Form 2553, generally due within two months and fifteen days of the start of the tax year it should take effect, with eligibility rules (shareholder limits, one class of stock, eligible shareholders) that must hold not just at election but continuously. Missed deadlines are common enough that the IRS built a standing remedy: Rev. Proc. 2013-30 grants late-election relief when its requirements are met, with the required representations attached. Our Taxflows library generates the election and late-relief request documents themselves.
§83(b): thirty days, no extensions
When founders take stock subject to vesting, the §83(b) election is the one deadline in the formation cluster with no relief at all: thirty days from the transfer of the stock. Filed, it moves taxation to grant, when the value is usually minimal; missed, each vesting date becomes a taxable event at the then-current value. The IRS now accepts the election on Form 15620. Our box-by-box walkthrough covers every field, and the classic founder case where the income reported is zero.
State of formation is its own question
Delaware is the default for venture-backed corporations, but the formation state is a separate question from where the business will owe taxes. That follows its actual activity. A company formed in one state and operating in another typically ends up registered, filing, and paying in both. When the choice is genuinely open, comparing the candidates' actual rules side by side is the honest way to decide. That's what the State Tax Matrix does, cited to each state's own authority.
From analysis to filing
Formation questions end in documents: the election, the statement, the relief request. The AI Tax Assistant handles the analysis, answered from the Code and regulations with clickable citations, and Taxflows generates the filing documents themselves, free, no login. Ask the question, then generate the election that makes the answer stick.
Shashank Sharma is the founder of Partnertax.ai, an AI tax assistant for tax professionals, built on cited IRS and Treasury sources.