Double-trigger acceleration is a vesting term that speeds up an equity holder’s unvested shares only when two events both happen, typically a change of control of the company plus an involuntary termination within a set window after that deal.

Founders care because acceleration terms decide whether a key hire keeps vesting through an acquisition or walks away fully vested on day one. Buyers price this in, and the wrong default can complicate or reprice your exit.

Single-trigger versus double-trigger acceleration

Single-trigger acceleration needs only one event, usually the change of control itself. On closing, some or all unvested equity vests automatically. Employees like it. Acquirers dislike it, because it can leave them with a paid-out team that has no reason to stay.

Double-trigger acceleration needs two events together. A change of control alone does nothing. Vesting accelerates only if a second trigger also occurs, most often the employee being terminated without cause or resigning for good reason within a defined period after the deal. That window is commonly 12 months, though it is negotiated.

Double-trigger is the market-standard compromise for founders and senior hires. It protects the person if the acquirer pushes them out, while keeping the retention incentive the buyer wants. This is contract practice, not a statute, so the exact triggers live in the equity documents and any offer letter or plan.

How double-trigger acceleration works in practice

Definitions do the heavy lifting. “Change of control,” “cause,” and “good reason” each need precise drafting, because they decide when the second trigger fires. Loose definitions create disputes at the worst possible time, mid-acquisition.

Consider a founder with a four-year vesting schedule who is two years in. The company is acquired, and 90 days later the buyer eliminates the role without cause. With full double-trigger acceleration, the remaining two years of unvested equity vest on that termination. Without it, the founder forfeits the unvested portion.

Acceleration can be full or partial, such as 100% or 12 months of extra vesting. It applies to shares subject to a vesting schedule, whether restricted stock or options drawn from the option pool. Founders who buy restricted stock at formation often pair the purchase with an 83(b) election, which is a separate tax step and does not change the acceleration terms.

This is general information, not legal advice.