Structural Change
C Corp to S Corp (and Back): Both Directions With the Tax Mechanics
Most articles cover one direction. Both have material and sometimes irreversible consequences. The S-to-C direction resets the QSBS clock, a major reason VC-track founders should not start as S-Corps.
Updated 17 April 2026 · Sources: IRC Sections 1374, 1375, 1362, 1363, 1377, 1202
Direction 1
C-Corp to S-Corp
File Form 2553 with shareholder consents
Built-in gains tax (IRC 1374)
Appreciated assets at conversion carry a 5-year recognition window. Sale within that window triggers 21% corporate tax on the built-in gain at the entity level, then again as pass-through. Get an appraisal at conversion date.
Passive income trap (IRC 1375)
If converted S-Corp carries over C-Corp E&P AND passive income exceeds 25% of gross receipts, highest corporate rate applies on excess passive income. Three consecutive years triggers automatic S election termination.
LIFO recapture (IRC 1363(d))
A C-Corp using LIFO inventory must include the LIFO reserve as income at conversion, spread over four years. Relevant for product businesses with significant inventory.
AAA starts at zero
The Accumulated Adjustments Account starts at zero on conversion. Track separately from carried-over C-Corp E&P. Distribution ordering: AAA first (tax-free), then C-Corp E&P (dividend), then return of capital.
Best practice: convert 1 January
Convert effective 1 January to avoid a split-year return. Distribute accumulated C-Corp E&P before conversion if possible to reduce the passive income trap risk.
Direction 2
S-Corp to C-Corp
Revoke by majority consent or allow terminating event
QSBS clock resets (IRC 1202)
QSBS five-year clock starts at the conversion date. Pre-conversion S-Corp appreciation is not QSBS-eligible. This is the most significant economic cost for founders converting before a fundraise.
Five-year re-election wait (IRC 1362(g))
After revocation or termination, cannot re-elect S status for five years without IRS consent. IRS consent is discretionary but routinely granted for genuine business purposes.
Post-Termination Transition Period (IRC 1377(b))
One year after S election terminates, distributions from AAA remain tax-free. After PTTP, all distributions become C-Corp dividends. Use the PTTP to distribute remaining AAA balances.
Accounting method change
A cash-method S-Corp may need to switch to accrual on conversion if gross receipts exceed the threshold ($31M in 2026). Section 481(a) adjustment spreads the change over four years.
Mid-year conversion mechanics
Creates an 'S short year' and a 'C short year' in the same calendar year under IRC 1362(e). Income allocated pro-rata or by specific identification. Two separate returns required for the year of conversion.
Conversion Comparison
| Factor | C-Corp to S-Corp | S-Corp to C-Corp |
|---|---|---|
| Mechanism | File Form 2553 with shareholder consents | File revocation statement; or allow terminating event |
| Main tax cost | Built-in gains recognition window (5 years, 21% corporate) | None immediate; QSBS clock resets from conversion date |
| QSBS impact | Prior C-Corp QSBS period intact; no QSBS accrues during S period | Clock resets; pre-conversion S-Corp appreciation not QSBS-eligible |
| Re-conversion wait | Can revert to C-Corp any time; re-electing S requires 5-year wait | 5-year wait to re-elect S status without IRS consent |
| Complexity | High (BIG tracking, E&P, LIFO, appraisals) | Medium (PTTP management, accounting method change) |
| Best timing | Effective 1 January (avoids split-year filing) | Before VC term sheet; before adding foreign shareholders |