Executive Summary
Quick Answer
Source: IRC Section 422(d); company plan documents
The $100K rule surprises employees who receive large ISO grants that vest quickly. The intent is to limit the tax-advantaged ISO regime—Congress did not intend unlimited ISO treatment.
Use our ISO $100K Limit Planner for a single-grant illustration and read on for multi-grant intuition.
The Formula (Conceptual)
For each calendar year:
- List shares that first become exercisable that year under each grant.
- Multiply by FMV per share at grant (409A for private companies).
- Cumulate until you reach $100,000 of ISO value for that year.
- Remaining shares that year are NSO for tax purposes.
Interactions with Vesting
| Pattern | Effect |
|---|---|
| Monthly vest after cliff | First calendar year after cliff may see a large “first exercisable” tranche |
| Back-loaded grants | May push more value into later years—still subject to annual test |
| Refresh grants | Each grant has its own grant-date FMV |
Planning Angles (High Level)
- Exercise sequencing: ISO vs NSO portions may have different tax outcomes—see ISO vs NSO.
- AMT: ISO exercises can still trigger AMT on the ISO portion—see AMT planning.
- 83(b): Early exercise elections are a separate decision—see Section 83(b) election.
Disclaimer
This article is educational. The ordering of tranches within a year can depend on plan language and administrator practices. Confirm with your stock admin and tax advisor.