Treat the entity choice as a checkpoint reviewed annually, not a permanent decision. A sole proprietor becomes an LLC, an LLC elects S-corp status, a successful S-corp converts to C-corp before a venture round — each transition has tax consequences, and the right time to make the transition is early, before the consequences scale. The conversions below describe the mechanics; the rule that ties them together is to convert on the upslope, never on the eve of a transaction that would amplify whatever tax the transition triggers.
Sole proprietor to LLC. Trivial. Forming a single-member LLC is a state filing; the IRS sees nothing change. A multi-member LLC formed from two or more sole proprietors is treated as a partnership formation under IRC §721, “Contributions to the partnership”, generally with no gain recognized on contribution unless liabilities transferred to the partnership exceed the contributor’s outside basis.
LLC to S-corporation (election only). An LLC that meets the S-corporation eligibility rules can elect S treatment on Form 2553 without changing its legal form. The IRS treats the LLC as a corporation that timely elected S status, and the LLC remains an LLC for state-law purposes. The election must be filed by the 15th day of the third month of the tax year in which it takes effect; a late election can sometimes be cured under Rev. Proc. 2013-30.
LLC to C-corporation (election or conversion). Two paths. The simpler is Form 8832 check-the-box, which leaves the legal form alone and elects association tax treatment. The other is a statutory conversion to a corporation under state law, generally tax-free under IRC §351 if the existing owners receive at least 80% of the new corporation’s stock in exchange for their LLC interests. The conversion route is standard when raising priced equity from institutional investors — venture funds will not buy LLC interests.
S-corp to C-corp. Revoke the S election by filing a statement of revocation with the IRS, retroactive to the start of the year if filed by the 15th day of the third month. The trap: once an S election is revoked, the corporation cannot re-elect S status for five years without IRS consent ( IRC §1362(g), “S corporation defined”). Owners considering a revocation to take advantage of C-corp fringe benefits or to position for a QSBS-eligible financing should be certain — the five-year clock is not negotiable.
C-corp to S-corp. File Form 2553 for the new S election. The corporation is taxed as a pass-through prospectively, but appreciation that existed at the conversion date is subject to the IRC §1374, “Tax imposed on certain built-in gains” built-in-gains (BIG) tax: if the corporation sells appreciated assets within five years of the conversion, the gain that existed on the conversion date is taxed at the C-corporation rate, on top of the pass-through tax on any additional appreciation. Sequence the conversion to clear the five-year recognition window before any anticipated asset sale — which usually means converting at the earliest sign that the business has begun to appreciate, while the embedded gain is still small, rather than waiting until a buyer is at the table. Convert early and let the clock run while the business grows; do not convert in the year before sale.
QSBS clock implications. The IRC §1202 holding period starts on the date the C-corporation issues the stock. An LLC that converts to a C-corporation under IRC §351 starts the clock on the conversion date — not the date the LLC was originally formed. The same holds for any IRC §351 contribution that creates new C-corp stock. For a founder who has been operating as an LLC for years and is now contemplating a C-corp conversion, the five-year QSBS clock has not yet started and will not begin until the conversion is complete.