Six weeks before our first acquisition offer showed up, our lawyer asked me a question I couldn't answer: is your vesting single-trigger or double-trigger? I'd signed my founder stock purchase agreement two years earlier without asking. I had no idea. Neither did my co-founder.
That's the moment I learned this clause doesn't matter until the day it's the only thing that matters, and by then it's usually too late to renegotiate.
What the clause actually controls
Acceleration clauses decide what happens to your unvested equity when the company gets acquired. Without one, an acquirer buys the company, and your unvested shares just keep vesting on the original schedule under whoever owns the cap table now, if they even let them keep vesting at all. With one, some or all of that unvested equity vests immediately, on a trigger you negotiated years earlier.
Single-trigger acceleration vests everything the moment the acquisition closes, full stop. Double-trigger requires two events: the acquisition, and then you being let go or demoted within a set window afterward, usually twelve months. If the acquirer keeps you on in your role, double-trigger equity keeps vesting on the original schedule like nothing happened.
Why founders sign it blind
Nobody negotiates this at incorporation because nobody's thinking about an exit yet. Then it shows up again at the priced round, buried in a term sheet next to liquidation preferences and board composition, the two things every founder actually reads closely. Acceleration language gets whatever the lawyer's template defaults to, and investors have a strong, consistent preference: double-trigger. It protects the deal they're trying to close later, not you.
I'm not arguing double-trigger is wrong. For most seed and Series A rounds, it's the market standard for a reason, and pushing for single-trigger can spook an acquirer who wants you around post-close. The problem isn't which one you end up with. It's that most founders never actually choose. They inherit whatever the template said, find out what it means the week a term sheet from an acquirer lands, and by then the leverage to change it is gone.
The 3-question test to run before you sign anything
Question one: how much of your equity is still unvested, and does that number change a lot over the next year? A founder eighteen months in with half their grant still unvested has real money riding on this clause. A founder in year four with 90% vested mostly doesn't.
Question two: are you the founder an acquirer will want to keep, or the one they're likely to let go within a year? Product and engineering founders often get retained and re-comp'd. Founders whose role was mostly external, sales, fundraising, partnerships, get cut faster once the acquirer has their own team for that. If you're honestly in the second category, double-trigger's twelve-month window is the exact window you're likely to get cut inside, which actually works in your favor. If you're in the first category and expect to stay for years post-close, the clause barely matters either way.
Question three: is this being negotiated at the term sheet stage, where you have leverage, or after you've already signed, where you don't? This is the one founders get wrong most often. Acceleration terms are cheap to negotiate before a priced round closes and nearly impossible to reopen afterward without raising red flags about your commitment to the company. If you're mid-negotiation on a term sheet right now, this is the week to ask, not the year an acquirer shows up.
The math that made this real for me
When the acquisition offer came in, I ran the numbers on both scenarios. My unvested stake at that point was worth roughly $1.4M at the offer price. Under single-trigger, that full amount would have vested the day the deal closed, no matter what happened to my role afterward. Under double-trigger, which is what we actually had, it only vested if the acquirer let me go or materially changed my role within twelve months of closing.
The acquirer kept me on running the same product for the next year, so my double-trigger equity kept vesting on the original monthly schedule instead of showing up as a lump sum at close. I didn't lose the $1.4M, but I didn't get it early either, and for a few weeks before I understood the mechanics, I genuinely didn't know which outcome I was looking at. That's an uncomfortable way to find out what your own agreement says, in the middle of the biggest financial event of your career.
What I'd tell a founder negotiating this today
Ask your lawyer directly which trigger structure is in your current agreement, this week, not during diligence. If you're heading into a priced round, put acceleration on the same list as valuation and board seats, it's cheap to negotiate now and expensive to revisit later. And run the three-question test honestly: know your unvested number, know which kind of founder you are to a likely acquirer, and negotiate while you still have leverage to negotiate with. The clause you never think about is the one that decides what happens on the one day it's the only thing that matters.