Founder Vesting Acceleration: Single vs Double Trigger
Vesting decides when your founder shares are truly yours. Acceleration decides what happens to the unvested shares if the company is sold before your schedule runs out. It is a short clause buried in a long document, yet it can change what you walk away with after years of work. Here is how single and double trigger acceleration work, why investors care, and how to talk about it calmly when the term sheet arrives.
Key takeaways
- Acceleration lets some or all unvested founder shares vest early when a specific event happens, usually a sale of the company.
- Single trigger acceleration needs only one event: the sale. Double trigger needs a sale plus termination without cause or resignation for good reason.
- Double trigger is the more common founder arrangement (rule of thumb), because it protects you without scaring off buyers.
- The definitions of "cause", "good reason" and "change of control" matter as much as the trigger type, so read them closely.
If you have co-founders and outside investors, someone will eventually ask you to put your shares on a vesting schedule. Vesting protects everyone, including you, from a co-founder who leaves in month six and keeps a third of the business. Acceleration is the flip side of that protection. It answers a fair question: if the company is sold and the new owner no longer needs you, should you lose the shares you were still earning?
A quick note before we go further: this article is general information, not legal, tax or investment advice. Vesting and acceleration terms interact with corporate law, tax rules and your specific deal documents. Work with a startup lawyer and a tax professional before you sign anything.
Vesting in one minute
Founder vesting means your shares are issued up front but the company can buy back the unvested portion if you leave before a set date. Each month or quarter that you stay, more of your shares become fully yours.
There are a few moving parts worth naming, because acceleration clauses refer to them directly:
- Vesting start date. Often the date the company was formed or the date you started full time. Founders sometimes get credit for time already worked.
- Cliff. The first point at which any shares vest. Leave before the cliff and, in a typical setup, none of your shares have vested.
- Vesting schedule. How the rest vests after the cliff, usually in equal monthly slices.
- Repurchase right. The company's right to buy back unvested shares, usually at the original low price, if you leave.
In the US, founders who receive restricted stock that vests over time often file an 83(b) election within 30 days of receiving the stock. That choice affects how and when you are taxed on the shares as they vest. The 30-day window is strict, so put it on your calendar the day the stock is issued and ask your tax adviser how it applies to you.
What acceleration actually does
Acceleration is a clause that speeds up vesting when a defined event happens. Instead of waiting for the schedule to run its course, some or all of your unvested shares vest immediately.
Acceleration can be:
- Full. All unvested shares vest at once.
- Partial. A set portion vests, such as a fraction of the remaining shares or a fixed number of months of extra vesting.
- Triggered by one event or by two. This is the single versus double trigger question, and it is where most of the negotiation happens.
The event that starts the clock is usually called a "change of control." In plain language, that means the company is sold, merged into another company, or sells most of its assets. Your documents will define it precisely, and that definition deserves a careful read.
Single trigger acceleration explained
With single trigger acceleration, one event is enough: the sale of the company. The moment the deal closes, your unvested shares (or the agreed portion) vest. It does not matter whether the buyer keeps you, promotes you or lets you go.
Why founders like it
Single trigger is simple and certain. You built the value the buyer is paying for, and this clause makes sure you share in it even halfway through your schedule.
Why investors and buyers push back
Buyers usually want key people to stay after a sale, at least for a transition period. Unvested equity is one of the main reasons people stay. If every founder's shares vest the day the deal closes, the buyer may have to offer new retention packages, which can come out of the price everyone receives. Some buyers may simply walk away. Investors know this, so they often resist full single trigger acceleration because it can make the company harder to sell.
Common mistake
Treating full single trigger acceleration as a pure win. If it makes a future buyer nervous, the cost can show up as a lower offer, a more complicated earnout or a deal that never happens. A clause that looks generous on paper can quietly shrink the outcome for you and your team.
Double trigger acceleration explained
Double trigger acceleration needs two events before your shares vest early:
- A change of control. The company is sold or merged, as defined in your documents.
- A qualifying departure. Within a set window after the sale, you are terminated without cause, or you resign for good reason.
If both happen, the agreed portion of your unvested shares vests. If the buyer keeps you on in a fair role, your vesting simply continues on its normal schedule.
Double trigger is the more common founder arrangement (rule of thumb). It balances both sides: the buyer still has a reason for you to stay, and you are protected from being pushed out after the sale and losing the equity you were still earning.
The definitions that make or break it
Double trigger protection is only as strong as the words that define it. Spend time on these with your lawyer:
- Cause. This should cover genuine misconduct, such as fraud or a serious breach, not vague things like "poor performance." A narrow definition protects you.
- Good reason. This lets you resign and still get acceleration if the buyer makes your job meaningfully worse. Typical examples include a big pay cut, a major reduction in responsibilities, or a forced move to a distant location. Many clauses also require you to give notice and allow time for the company to fix the issue.
- The window. The period after the sale during which a termination counts. Some documents also cover a short period before the sale, in case someone is let go just before closing.
- Change of control. Check whether a large financing round could accidentally count. Usually it should not.
Pro tip
Read the "good reason" definition as if you were the buyer trying to avoid paying out. Ask: could they cut my role in half without technically triggering this? If the answer is yes, the protection may be weaker than it looks.
Single vs double trigger side by side
Here is a quick comparison you can keep next to your term sheet. It describes how these clauses usually work; your own documents may differ.
| Single trigger | Double trigger | |
|---|---|---|
| What starts acceleration | Sale of the company alone | Sale plus termination without cause or resignation for good reason |
| If the buyer keeps you on | Shares still accelerate | Normal vesting continues |
| Founder protection | Strongest and simplest | Strong, if definitions are fair |
| Effect on buyers | Can reduce retention incentive | Keeps a reason to stay after the sale |
| How common for founders | Less common, often partial | More common (rule of thumb) |
Some founders land on a blend: a small portion accelerates on the sale alone, with more accelerating under double trigger conditions. This hybrid gives you something certain while keeping the buyer comfortable.
Worked example with made-up numbers
Hypothetical example
Priya co-founded a software startup and holds 1,000,000 shares on a 4-year schedule with a 1-year cliff. Two and a half years in, 625,000 shares have vested and 375,000 are still unvested. The company is acquired.
Scenario A, single trigger, full acceleration: all 375,000 unvested shares vest when the deal closes, whatever happens to Priya's job.
Scenario B, double trigger, full acceleration: the buyer keeps Priya as head of product. Her shares keep vesting on schedule. Eight months later, the buyer lets her go without cause. Because both triggers have now occurred within the agreed window, her remaining unvested shares vest.
Scenario C, double trigger, 50% acceleration: same facts as B, but only half of the shares that were unvested at the time of termination vest early. The rest are lost.
All figures here are invented for illustration. Real outcomes depend on the exact deal terms, how the buyer converts or assumes the shares, and tax treatment.
How to talk about acceleration with investors
Acceleration usually comes up when an investor asks founders to vest (or re-vest) their shares as part of a priced round. Treat it as a normal part of the conversation, not a battle.
- Understand your starting point. Check whether your current founder stock agreements already include vesting or acceleration, and what the investor's term sheet proposes.
- Ask for credit for time served. If you have already worked on the company for a while, it is common to ask for some vesting credit rather than starting from zero.
- Propose double trigger with fair definitions. It is a reasonable, familiar ask. Focus your energy on the definitions of cause and good reason.
- Decide how much should accelerate. Full or partial is a real choice. Think about what a buyer would see and what you would feel is fair.
- Keep co-founders aligned. Most teams use the same terms for every founder, which avoids resentment later.
- Let your lawyer draft the wording. Small phrasing differences matter a lot here.
Questions to ask before you sign
Copy this into your notes and bring it to your next call with your lawyer:
| Question | Why it matters | Example answer to aim for |
|---|---|---|
| Is it single, double or a hybrid? | Sets the basic level of protection | Double trigger, possibly with a small single trigger slice |
| How is "good reason" defined? | Decides whether a forced demotion counts | Covers material pay cuts, role reductions and relocation |
| How long is the window after a sale? | A short window weakens protection | A clearly stated period agreed with your lawyer |
| Does it cover termination just before closing? | Prevents a pre-sale firing loophole | Yes, for a short defined period |
Acceleration for employees and option holders
Similar clauses can appear in employee option grants, such as US ISOs or NSOs and UK EMI options. Employee acceleration is usually less generous than founder acceleration, and many companies offer it only to senior hires. Whatever you choose, write it into your equity plan so everyone knows the rules.
Your acceleration checklist
- Find your current founder stock agreement and read the vesting section
- Confirm your vesting start date, cliff and schedule
- If you received restricted stock in the US, confirm the 83(b) election was filed within 30 days
- Check whether you have single, double or no acceleration today
- Read the definitions of cause, good reason and change of control
- Decide what you would ask for: full or partial, and how long a window
- Align terms with your co-founders
- Review the final wording with a startup lawyer before signing
Frequently asked questions
Is double trigger acceleration standard for founders?
It is the more common arrangement as a rule of thumb, but nothing is truly standard. Terms vary by investor, market conditions and how much leverage you have. Treat it as a reasonable starting point for discussion rather than a guarantee.
Can I add acceleration after the company is already set up?
Often yes, by amending your stock agreements, but it usually needs board approval and may need investor consent. It is easiest to agree on it during a financing round when vesting terms are already on the table. Ask your lawyer about the process.
What happens to unvested shares without any acceleration?
It depends on the deal. A buyer might convert your unvested shares into unvested shares or cash in the new company, continuing your schedule. If you are later let go, you could lose whatever had not vested. That risk is exactly what double trigger acceleration addresses.
Does acceleration change my taxes?
It can affect timing, especially if you did not file an 83(b) election in the US. Tax treatment depends on your country, how the shares were issued and the deal structure, so speak to a tax professional before and during any sale.
Related reading
The bottom line
Vesting protects the company from a founder who leaves early. Acceleration protects you from losing the equity you were still earning when the company is sold. Single trigger is the simplest protection but can worry buyers. Double trigger is the more familiar middle ground, and its real strength lives in the definitions of cause, good reason and the time window.
Read your current agreement this week, note what you have today, and bring the question list above to your lawyer before the next term sheet lands. A calm hour now can save you a painful surprise years from now.
