Equity Compensation, IRC Section 422 ISOs & Alternative Minimum Tax
ISO Stock Option Bargain Element & AMT Crossover Formula
Calculate Incentive Stock Option (ISO) Form 6251 Bargain Element ($k), Tentative Minimum Tax TMT ($k), Incremental Cash AMT Payable ($k), and Maximum AMT-Free Exercise Shares (k).
Exercising and holding ISOs avoids regular W-2 withholding—but triggers Form 6251 cash AMT!
Unlike Non-Qualified Stock Options (NSOs), exercising and holding Incentive Stock Options (ISOs, IRC §422) triggers zero regular W-2 tax at exercise. However, under IRC §56(b)(3), the entire ISO Bargain Element = Shares * (Exercise_FMV - Strike_Price) is added directly to Alternative Minimum Taxable Income (AMTI) on IRS Form 6251! Whenever Tentative Minimum Tax TMT = (Regular_Taxable_Income + Bargain_Element - AMT_Exemption) * AMT_Rate exceeds Regular Federal Tax, the employee owes the excess as cash AMT—and solving TMT = Regular_Tax gives the exact Maximum AMT-Free ISO Shares = MAX(0, ((Regular_Tax / AMT_Rate + AMT_Exemption) - Regular_Income) / (FMV - Strike))!
Verify on a Senior Engineer Year-End Exercise—Regular_Taxable_Income = $250.00k (B2), Regular_Federal_Tax = $56.00k (B3), ISO_Shares_Exercised = 10.00k (10,000 shares, B4), ISO_Strike = $4.00/sh (B5), Exercise_Date_FMV = $24.00/sh ($20.00/sh spread, B6), and Available_AMT_Exemption = $85.00k at a 28.0% marginal AMT rate (B7): Form 6251 Bargain Element hits $200.00k (E2), Tentative Minimum Tax reaches (250 + 200 - 85) * 0.28 = $102.20k (E3), Extra Cash AMT Payable is 102.20 - 56.00 = $46.20k (E4), and the Maximum AMT-Free Crossover Cap was ((56 / 0.28 + 85) - 250) / 20 = 1.75k (1,750 shares, E5)!
| Form 6251 ISO Exercise KPI ($250k Inc, $56k Reg Tax, 10k ISOs @ $4->$24, $85k Exemp) | Formula | Verified Output |
|---|---|---|
| ISO Bargain Element ($k) | ISO_Shares_k * (Exercise_FMV - Strike) | $200.00k ($35.00k @ 1.75k Sh) |
| Tentative Minimum Tax TMT ($k) | MAX(0, (Reg_Inc + Bargain - Exemp) * 0.28) | $102.20k ($56.00k @ 1.75k Sh) |
| Extra Cash AMT Payable ($k) | MAX(0, TMT_k - Regular_Tax_k) | $46.20k ($0.00k @ 1.75k Sh) |
| Max AMT-Free ISO Shares (k) | MAX(0, ((Reg_Tax/0.28 + Exemp) - Reg_Inc) / Spread) | 1.75k (1,750 Shares) |
Form 6251 Incremental AMT & Zero-AMT Crossover Share Formula
Validate Regular_Income >= 0, Regular_Tax >= 0, ISO_Shares_k >= 0, 0 < Strike < Exercise_FMV, and AMT_Exemption >= 0!
=LET(rg_i, B2, rg_t, B3, sh_k, B4, st_p, B5, fm_v, B6, ex_m, B7, IF(OR(rg_i < 0, rg_t < 0, sh_k < 0, st_p <= 0, fm_v <= st_p, ex_m < 0), "Invalid ISO Exercise Input", LET(bg_k, sh_k * (fm_v - st_p), tm_t, MAX(0, (rg_i + bg_k - ex_m) * 0.28), ROUND(MAX(0, tm_t - rg_t), 2))))Exact AMT-Free Crossover Verification Check (Set ISO Shares Exercised = 1.75k)
Trim ISO_Shares_Exercised_k B4 from 10.00k down to the crossover cap E5 = 1.75k (1,750 shares): Bargain Element E2 equals $35.00k, Tentative Minimum Tax E3 matches Regular Tax at exactly $56.00k, and Extra Cash AMT Payable E4 drops to $0.00k!
=IF(ISTEXT(E4), E4, ROUND(MAX(0, ((B3 / 0.28 + B7) - B2) / (B6 - B5)), 2))Try the example
Use the original values or change them to test your understanding.