What is Treasury Regulation §1.422-4?

It is the Treasury regulation that implements IRC §422(d), including how to apply the $100,000 limit to incentive stock options based on grant-date fair market value and shares first exercisable in a calendar year.

How is the $100K ISO limit calculated?

Generally using the aggregate fair market value at grant of stock for which ISOs first become exercisable in a calendar year; amounts in excess of $100,000 may be treated as non-qualified options—confirm grant ordering and plan terms.

Does this replace my ISO bifurcation guide?

No—this page focuses on the regulatory citation and mechanics; the bifurcation guide covers broader scenarios and examples.

Where can I model my vesting against the cap?

Use the ISO $100K limit calculator and multi-year planner on the Tools page.

Is 26 CFR 1.422-4 the same as IRC 422(d)?

The IRC sets the statutory rule; the Treasury regulation provides administrative detail—both must be read together with your plan documents.

Should I rely on this for tax filing?

No—this is educational. Use a qualified tax professional and your employer’s equity reporting.

ISO $100K Limit & Treasury Regulation 1.422-4: How the Cap Works

Key Takeaways

The $100K figure uses grant-date FMV × shares first exercisable in that calendar year

Regulations specify how to allocate when a single grant spans ISO and NSO treatment

Multiple grants from the same employer group are considered together

Plan documents and board approvals should reflect bifurcation—payroll must withhold correctly on NSO portions

Use the ISO $100K limit calculator to model vesting schedules against the cap

Executive Summary

Quick Answer

What does Treasury Regulation §1.422-4 say about the ISO $100K limit?

It operationalizes IRC §422(d): incentive stock options are limited so that the aggregate fair market value (determined at grant) of stock for which options first become exercisable in any calendar year cannot exceed $100,000. The portion of an option that exceeds the limit is treated as a separate non-qualified stock option. Exact allocation depends on grant ordering, vesting, and plan terms—confirm with your stock admin and tax advisor.

Source: Treasury Regulation §1.422-4; IRC §422(d)

Employees searching 26 CFR 1.422-4 or the ISO $100k limit rule usually need the bridge between the statute (IRC §422(d)) and how administrators apply it in practice. This article is a regulatory companion to our broader ISO $100,000 Annual Limit & Bifurcation Guide and the ISO $100K limit calculator.

The bottom line: The regulation is dense; your grant notices and first-exercisable dates drive the math. When in doubt, reconcile against payroll and Form 3921 at year-end.

Why §1.422-4 Exists

Section 422(d) caps ISO treatment so high-value grants cannot receive unlimited ISO benefits. The Treasury regulations under §1.422-4 spell out timing, valuation at grant, and split treatment when only part of a tranche qualifies as ISO.

Core Mechanics (Simplified)

Concept	Role
Grant-date FMV	Values shares for the $100K test (not exercise-date price)
First exercisable	Options count in the year they first could be exercised under the plan
Excess over $100K	Generally treated as NSO for tax purposes
Multiple grants	Often stacked in grant order when several become exercisable the same year

Source: Treasury Regulation §1.422-4; read the full regulation for definitions.

Relationship to Tools and Other Guides

ISO $100K Limit Calculator — model vesting and ISO vs NSO split.
ISO $100K Multi-Year Planner — spread exercises across years.
ISO vs NSO — tax comparison once bifurcation applies.
ISO $100K Rule: Multiple Grants — practical stacking scenarios.

Disclaimer: This article is for education only and is not tax or legal advice. ISO and NSO characterization is fact-specific. Consult a qualified CPA or equity counsel.