A clause that speeds up vesting under certain conditions, typically an acquisition or termination. Single-trigger acceleration vests on one event (like acquisition). Double-trigger requires two events (acquisition plus termination).
acceleration
/əkˌseləˈreɪʃən/ noun — In equity compensation, a contractual provision that causes unvested equity to vest immediately upon the occurrence of a specified triggering event. Acceleration clauses exist to protect founders and employees from losing unearned ownership when major corporate events — particularly acquisitions or involuntary terminations — occur beyond their control.
Why it matters
Acceleration clauses protect founders and key employees during major company events. Without one, you could lose unvested equity in an acquisition even if you helped build the company. Negotiating the right type of acceleration before it's needed is far easier than trying to get it after a deal is on the table.
Consider the scenario: you've been at a startup for two years, you have two more years of unvested equity, and the company is acquired. Without an acceleration clause, your unvested shares belong to the acquirer's vesting schedule — or disappear entirely if the acquirer doesn't honor them. An acceleration clause ensures you receive credit for the equity you helped earn through your work.
For co-founders, acceleration is especially important. A co-founder who builds a company to acquisition and then gets fired by the acquirer six months later deserves more protection than a standard vesting schedule provides. Double-trigger acceleration is designed precisely for this situation.
How it works
Single-trigger acceleration vests all (or a portion of) your unvested shares when one event happens, like the company being acquired. Double-trigger requires two events — typically an acquisition plus you being terminated or having your role significantly changed within a defined period afterward (usually 12-18 months). Double-trigger is more common because it keeps employees incentivized to stay through a transition.
For example, if you have two years of unvested shares and the company gets acquired, single-trigger would vest everything immediately. Double-trigger would only vest if you were also let go within 12 months of the acquisition. The "involuntary termination" definition in the agreement matters enormously — it typically includes termination without cause, significant reduction in compensation or responsibilities, or forced relocation.
Acceleration provisions can cover 100% of unvested shares or a partial percentage — say, 12 months of additional vesting. Some agreements distinguish between single-trigger events (which might accelerate 50%) and double-trigger events (which accelerate 100%). These details must be negotiated and documented in the original equity agreement.
| Type | Trigger events | Who uses it | Investor view |
|---|---|---|---|
| Single-trigger | Acquisition alone | Some co-founders | Disfavored — reduces acquirer incentive |
| Double-trigger | Acquisition + termination | Founders, employees | Preferred — maintains retention incentive |
| Partial acceleration | Either trigger type | Mid-level employees | Acceptable — balanced approach |
| No acceleration | None | Early employees (often) | Default — all unvested shares subject to acquirer's discretion |
History and origin
Acceleration provisions emerged as a byproduct of Silicon Valley's acquisition-heavy culture in the 1990s. As technology companies began aggressively acquiring competitors and talent, the question of what happened to unvested equity in a deal became increasingly contentious. Founders who had built companies to acquisition found themselves subject to the acquirer's discretion on their remaining equity.
The early venture capital model — which required founder vesting as a condition of investment — created the problem. VCs insisted on vesting to protect against co-founder departures, but that same vesting created vulnerability at exit. The acceleration clause evolved as the solution: a negotiated provision that ensured founders would receive their equity at acquisition, particularly if they were forced out.
Double-trigger acceleration became the dominant standard through the late 2000s and 2010s as institutional investors standardized term sheets. Y Combinator's model documents and the NVCA standard terms both incorporated double-trigger language, and today it is effectively the default in venture-backed startups. Single-trigger acceleration, while still occasionally negotiated for co-founders, has become increasingly rare due to acquirer resistance.
Frequently asked questions
What is acceleration in equity vesting?
Acceleration is a clause in a vesting agreement that causes some or all unvested equity to vest immediately upon a triggering event — typically an acquisition, merger, or involuntary termination. It protects founders and employees from losing unvested shares due to circumstances outside their control.
What is the difference between single-trigger and double-trigger acceleration?
Single-trigger acceleration vests equity on one event alone, most commonly an acquisition. Double-trigger acceleration requires two events — usually an acquisition followed by an involuntary termination or significant role change within a set window (typically 12-18 months). Double-trigger is far more common because it keeps employees motivated through the transition period.
Why do investors prefer double-trigger over single-trigger acceleration?
Investors and acquirers prefer double-trigger because single-trigger acceleration can create a perverse incentive: employees who know they'll vest everything upon acquisition may stop working hard or may resist deals. Double-trigger preserves the retention incentive through the acquisition and integration period, which is critical for the acquirer's return.
Can you negotiate acceleration provisions?
Yes, acceleration provisions are negotiable. The type of acceleration, the percentage of shares that accelerate, and the definition of triggering events are all negotiable terms. For co-founders, it's easiest to negotiate these terms at formation, before any investors are involved. For employees, acceleration is typically negotiated at the time of the offer.
What percentage of unvested shares typically accelerates?
This varies widely and is fully negotiable. Some agreements accelerate 100% of unvested shares. Others accelerate 50% (partial acceleration). Some accelerate only a fixed number of months of additional vesting. Full acceleration is more common for co-founders; partial acceleration is more typical for employees.
Does acceleration apply to all types of equity?
Acceleration provisions can apply to restricted stock, stock options, RSUs, or any other form of equity subject to a vesting schedule. The specific terms depend on what is written in the stock purchase agreement, option agreement, or RSU award agreement. Not all equity grants include acceleration — it must be explicitly negotiated and documented.
What counts as a triggering event for double-trigger acceleration?
The second trigger is typically an "involuntary termination" within a specified period (often 12-18 months) after the first trigger. Involuntary termination usually includes being fired without cause, having your role materially diminished, a significant reduction in compensation, or being required to relocate. The exact definition matters enormously and should be reviewed carefully by an attorney.
Learn more
- Vesting explained: cliffs, acceleration, and the schedule that protects everyone
- Vesting schedules explained: cliff, graded, and the 4-year standard
- Founder agreements: what to include
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