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You've been building your company for years. An acquirer makes an offer. The deal closes. Your unvested shares: do they vest or not?
The answer depends on your acceleration clause. And the difference between single-trigger and double-trigger acceleration can mean the difference between a clean exit and a messy one.
This guide explains what each means, how they affect acquisitions, and which one you should actually negotiate for.
What is vesting acceleration?
Standard vesting schedules run over four years with a one-year cliff. If you leave before the schedule is complete, the company repurchases your unvested shares. Simple.
But what happens when the company is sold before your vesting is complete? Acceleration clauses modify the standard schedule in specific situations, allowing some or all of your unvested equity to vest earlier than planned.
Single-trigger acceleration
Single-trigger means your unvested shares vest upon a single event. Usually, that event is the sale of the company.
How it works: the acquisition closes, and all (or a portion) of your unvested shares vest immediately. You're fully paid out at closing.
When it sounds good: you've been building for three years, you have one year of unvested equity remaining, and the acquirer is paying cash. Single-trigger means you get everything at close.
When it backfires: the acquirer sees that every founder and key employee will be fully vested on close. There's no incentive for anyone to stick around post-acquisition. The buyer either negotiates a lower price, demands new retention packages, or both. Your investors push back because the automatic vesting dilutes the deal economics.
Single-trigger can also be tied to involuntary termination: if you're fired without cause, your unvested shares vest. This can be part of a severance arrangement, but it requires careful drafting. "Without cause" can be broad enough to cover scenarios beyond misconduct, and the company may end up losing equity in situations that weren't intended.
Double-trigger acceleration
Double-trigger requires two events before unvested equity accelerates:
First trigger: the company is sold.
Second trigger: you're terminated without cause, or you resign for "good reason," within a defined window after closing.
That window is typically 9 to 18 months. Some agreements also include a short pre-closing window (e.g., 3 months) to prevent the company from terminating you just before the deal closes to avoid the acceleration payout.
How it works in practice: the acquisition closes. Your vesting continues on its normal schedule. If the acquirer keeps you on, you keep vesting. If they let you go within the specified window, your remaining shares accelerate.
Why double-trigger is the standard
Double-trigger is preferred by investors, acquirers, and experienced founders for several reasons:
For founders: you're still protected. If the acquirer pushes you out, your equity accelerates. You're not left with unvested shares that evaporate.
For acquirers: there's a retention incentive. You haven't already cashed out, so you have a reason to stay and help with the transition.
For investors: the deal isn't weighed down by automatic vesting at close. The cap table stays cleaner, and the economics of the deal hold.
The critical detail most people miss
Double-trigger acceleration only works if the acquirer assumes your existing equity plan. If they don't assume your stock agreements, there's nothing left to accelerate.
This is a negotiation point in the acquisition itself. Your legal team needs to ensure that either the equity plan is assumed or that there's a cash-out provision that accounts for the acceleration rights.
Which should you negotiate?
For most founders, double-trigger is the right choice. It protects you in the scenarios that matter (getting pushed out after a sale) without creating the problems that single-trigger introduces (buyer pushback, investor concerns, lower deal price).
Single-trigger may be appropriate in narrow situations, like a key executive with significant leverage, or when tied specifically to an involuntary termination (not a company sale).
The specifics matter. The definition of "cause," the definition of "good reason," the length of the post-closing window: all of these affect whether your acceleration clause actually protects you.
The bottom line
Acceleration clauses are one of those terms that feel theoretical until they're not. When an acquisition happens, the language in your stock agreement determines whether your years of work are fully rewarded or partially lost.
At Fellow, we structure acceleration clauses that protect founders without creating deal friction. If you're setting up equity agreements or reviewing terms before a raise, this is one of the details that deserves attention now, not at the negotiating table.
