Cofounder vesting acceleration decides what happens to your unvested equity the day your company gets acquired. It is a narrow clause, easy to skip while you are focused on the split and the cliff, and it is exactly the term that determines whether an acquisition pays you out or leaves you standing at the closing table with shares you can no longer earn. If you have not covered the standard vesting schedule yet, start there. This piece goes deeper, into the clause that only matters on the day your company gets bought.
The two trigger structures
Acceleration lets unvested shares vest early instead of waiting out the remaining months on the schedule. There are two structures, and the difference between them is the whole conversation.
Single-trigger acceleration vests all of your unvested shares the moment one event occurs, almost always a change of control. Sign the deal, and your equity is fully yours regardless of what happens next (Cooley GO).
Double-trigger acceleration requires two separate events before anything accelerates: the change of control, plus a qualifying termination — without cause, or a resignation for good reason — within a defined window after closing (Pulley). Get acquired and keep your role, and nothing accelerates. Get acquired and get pushed out within the window, and your unvested shares vest immediately.
Why single-trigger looks appealing and rarely survives
Single-trigger feels like the safer bet when you are the one negotiating it. It removes any dependency on an acquirer's good faith after closing: the shares are yours the day the deal signs, full stop.
The problem is what it does to the deal itself. Acquirers use unvested equity as retention leverage, the reason a key team stays through an integration instead of cashing out and leaving. Single-trigger removes that leverage entirely, and buyers notice (Capbase). A knowledgeable acquirer will price that risk into the offer, restructure the deal around it, or walk from founders who insist on it. Single-trigger acceleration has been waning for exactly this reason: it solves a founder's fear of a bad-faith acquirer at the cost of making the company itself harder to sell (Capbase).
Double-trigger has become the market standard because it threads the needle. It protects you from being pushed out with nothing after the people who bought your company no longer need you, while preserving the acquirer's ability to retain the team through the transition (Cooley GO). That is why investors will push back hard on single-trigger and rarely blink at double-trigger.
What actually gets negotiated
Once you accept double-trigger as the frame, three variables decide how much protection you actually have.
The percentage. Full acceleration of 100% of unvested shares is common in founder and CEO term sheets. Later hires and non-founding executives more often land at 50%, or a flat 12 additional months of vesting credited at termination (Pulley). There is no default here the way there is for the 4-year term — it is a straight negotiation, so put a number in writing rather than leaving it to be worked out later.
The window. Double-trigger only protects you if the termination happens inside a defined period after closing, typically 12 to 24 months (The Startup Law Blog). A termination that lands one day after a 12-month window closes gets nothing, even if it is obviously connected to the acquisition. Acquirers frequently restructure teams in waves, and the second wave often lands 12 to 18 months post-close — which is the practical argument for pushing your window to 18 or 24 months rather than accepting the first number offered.
How "cause" and "good reason" are defined. These definitions decide whether a demotion, a relocation requirement, or a materially reduced role counts as a trigger, or whether the acquirer can reshape your job without technically firing you. Vague language here can gut the protection the trigger was supposed to provide.
The failure mode nobody negotiates for
There is one scenario where double-trigger protection disappears no matter how well you negotiated the percentage and the window: if the acquirer cancels, cashes out, or swaps your unvested equity for something else the moment the deal closes, there is nothing left to accelerate later (Stock Option Counsel). Double-trigger acceleration only works if your unvested equity survives the transaction in some assumed or continued form.
This is the clause acquirers' counsel will try to leave loose, because a cancellation-without-payment structure quietly defeats every acceleration term you negotiated. The fix is a separate, explicit provision: if your unvested shares would otherwise be cancelled without payment under the deal terms, they vest immediately at closing instead. Without that backstop, your double-trigger clause is a promise that can be erased by how the acquisition is structured, not by anything you agreed to.
Where to put this in writing
Acceleration terms negotiated for the first time when a term sheet is already on the table are negotiated from a position of weakness — the deal has its own momentum, and clause-level fights get resolved fast. The better time is when you write the cofounder agreement and the role charter that sit underneath it, long before there is a buyer in the room.
Decide, in writing, while every cofounder is still aligned: single-trigger or double-trigger, what percentage accelerates, how long the window runs, and what happens if the acquirer cancels the unvested grant. Then make sure the language actually lands in the grant documents themselves, not just an offer letter that a later integration clause can override.
If you have not mapped where your partnership's assumptions are still unwritten, run the cofounder alignment check together, and pull a starting document from our free founders-agreement templates. Acceleration is a small clause. It only matters once, on the day your company is acquired, and by then it is too late to negotiate it from scratch.
Frequently asked questions
- What is the difference between single-trigger and double-trigger acceleration?
- Single-trigger acceleration vests all unvested shares the moment a single event occurs, usually an acquisition. Double-trigger acceleration requires two events: the acquisition, plus a qualifying termination (without cause, or resignation for good reason) within a defined window afterward, typically 12 to 24 months. Double-trigger is the investor-preferred market standard.
- Why do VCs push back on single-trigger acceleration?
- Single-trigger acceleration vests every unvested share the instant a deal closes, which removes the acquirer's ability to retain the team with unvested equity. Buyers price that risk into the deal or walk away from founders who insist on it, so investors treat single-trigger as a signal that can shrink the exit itself.
- What percentage of equity typically accelerates on a double trigger?
- It varies by role and negotiating leverage. Founders and CEOs often negotiate 100% acceleration on a qualifying termination. Later hires and non-founding executives more commonly see 50% acceleration, or 12 additional months of vesting credited at termination. There is no fixed rule, so put a specific number in writing.
- How long is the window for double-trigger acceleration?
- Most double-trigger provisions specify a window of 12 to 24 months after the change of control during which a qualifying termination triggers acceleration. A 12-month window is common but can miss a second wave of post-acquisition layoffs; founders with leverage often negotiate for 18 to 24 months instead.
- Does double-trigger acceleration protect you if the acquirer cancels your unvested shares at closing?
- Not automatically. Double-trigger acceleration only works if your unvested equity is assumed or continued by the acquirer after closing. If the buyer cancels, cashes out, or swaps your unvested grant for something new at the moment the deal closes, there is nothing left to accelerate later. Negotiate a separate provision for immediate vesting if your unvested shares would otherwise be cancelled without payment.
- Should cofounders write acceleration terms into the founders agreement or wait for a term sheet?
- Write them into the founders agreement and grant documents early. Acceleration terms negotiated for the first time during an acquisition or a financing round are negotiated from a position of weakness. Deciding the trigger type, the percentage, and the window while cofounders are still aligned protects everyone before there is a deal on the table.
