Acceleration Clause
A provision in a stock option or equity agreement that allows some or all unvested shares to vest immediately upon the occurrence of a specified triggering event, such as an acquisition or termination.
What Is an Acceleration Clause?
An acceleration clause is a contractual provision in an equity compensation agreement that causes unvested options or shares to vest immediately (or on an accelerated schedule) when a specific event occurs. These events are commonly referred to as "triggers." The most frequent triggers are a change of control (acquisition of the company) and involuntary termination of the employee. Acceleration clauses protect employees from losing unvested equity in situations where they might otherwise be unfairly affected by corporate events outside their control.
Acceleration clauses are negotiated — they are not automatic. Whether your equity includes an acceleration provision, and what type, depends on your offer letter, equity agreement, and sometimes the company's equity incentive plan.
How Acceleration Clauses Work
Single-Trigger Acceleration
A single-trigger acceleration clause causes unvested equity to vest upon a single event — typically a change of control (acquisition). If your agreement has single-trigger acceleration and the company is acquired, all (or a specified portion) of your unvested options vest immediately, regardless of whether you continue working at the acquiring company.
Single-trigger acceleration is more favorable for employees but less common, especially at venture-backed startups, because it can complicate acquisitions — acquirers want the retention incentive of unvested equity to keep key employees.
Double-Trigger Acceleration
A double-trigger acceleration clause requires two events to occur before acceleration kicks in: (1) a change of control, and (2) the employee's involuntary termination (or constructive termination) within a specified period, usually 12–24 months after the acquisition. The logic is that if you are kept on after the acquisition, your unvested equity continues vesting normally. But if you are laid off or your role is materially changed, your unvested equity accelerates.
Double-trigger acceleration is more common in practice and is generally considered the market standard for executive and senior employee agreements at venture-backed companies.
Partial vs. Full Acceleration
Acceleration can be full (100% of unvested equity vests) or partial (a specified percentage, such as 25% or 50%). Some agreements provide for 12 months of additional vesting upon a trigger event, which is functionally partial acceleration. The specifics are defined in the acceleration clause itself.
Constructive Termination
Many double-trigger clauses include "constructive termination" as a qualifying trigger. This means that if the acquiring company significantly changes your role, reduces your compensation, or requires relocation, you can resign and still receive the acceleration benefit. The definition of constructive termination varies by agreement and should be reviewed carefully.
Practical Implications for Startup Employees
Negotiate Before You Join
Acceleration clauses are most easily negotiated at the offer stage. Once you have joined and your equity agreement is finalized, it is much harder to add acceleration provisions. If you are joining a late-stage company where an acquisition is foreseeable, acceleration protection is especially valuable.
Acceleration in Acquisitions
In many acquisitions, the acquirer may choose to cash out unvested options at the acquisition price or convert them to acquirer equity. If your agreement includes acceleration, your unvested options vest and you receive the full benefit immediately. Without acceleration, the acquirer may terminate unvested options entirely (subject to the terms of the acquisition agreement and your equity plan).
Not All Acceleration Is Equal
Read the specifics of your acceleration clause carefully. Key variables include: what percentage accelerates, what events qualify as triggers, whether constructive termination is included, and what the time window is for the second trigger in a double-trigger clause. The difference between 50% acceleration and 100% acceleration can be worth tens or hundreds of thousands of dollars.
How It Relates to Exercising Stock Options
If your equity agreement includes an acceleration clause, it may affect your exercise planning. With single-trigger acceleration, an acquisition could suddenly vest all your options — creating a large exercise opportunity (and potential tax event) at the time of the deal. With double-trigger acceleration, your unvested equity is protected if you are terminated after an acquisition, giving you time to exercise during your post-termination exercise window. Understanding your acceleration terms helps you plan for these scenarios before they happen.