Finding the right co-founder is arguably the most important part of starting a company. I've seen so many startups fail or succeed due to co-founder issues. The relationship you build with your co-founder will determine not just your company's trajectory, but your own experience of building something meaningful.
Quite literally, a co-founder is someone who starts your startup with you. When you apply to incubator like YC, they consider someone to be your co-founder if they have at least 10% equity, but in general, a co-founder is someone who is there from the beginning or close to the beginning, who is building your company with you.
If I'm hardworking and smart, can I just start my startup alone? The short answer is yes, you absolutely can. But it's really hard—like really, really hard. A startup is a very difficult journey for anyone, and doing it alone makes it more than twice as hard.
We really recommend having a co-founder for several reasons:
Productivity: Moving fast is critical in a startup, and when you have two people or three people, you can literally move two or three times as fast. You can just get so much more stuff done. Additionally, your brainstorming can be higher quality. You can help each other see around corners and bounce ideas off each other. Maybe you won't get into a rut with a bad idea and have someone checking.
Accountability: It's a little bit more effective when there's someone else there. You do your daily standup and say, "This is what I'm going to get done today," and then there's someone there the next morning to ask you whether or not you did it.
Moral Support: This is another huge and sometimes overlooked component. A startup has a lot of ups and downs. There are moments of optimism, there are moments of despair, and having someone that can both empathize with you but also balance you out in some of those scenarios can be just so helpful to keep moving.
If you're not convinced by those theoretical reasons, it turns out that the empirical evidence also supports having a co-founder. Most successful companies have been started by more than one founder. Even companies that are famous for only one of its founders actually had at least two.
Microsoft—we all know Bill Gates, but Paul Allen was around for 10 years. Apple—Steve Jobs is the face of Apple, but Steve Wozniak was the one who designed and built the Apple computer. And little-known fact, they actually had a third co-founder, Ronald Wayne. He left pretty early, but there were three of them in the beginning.
Facebook, or I guess Meta now—if you've seen The Social Network, you'll know that Mark Zuckerberg had not one, not two, not three, but four co-founders.
The data is pretty compelling too. While YC does fund solo founders, of their top 100 companies, only four were founded by a solo founder. And in those cases, there's a clear pattern: the solo founders were always able to make progress on their own. They built their own MVP, they got their own users, etc.
So while having a co-founder dramatically increases your chances of success, incubator including YC actually does fund solo founders. They believe that ultimately you are the best judge of whether having a co-founder is the right call for you.
If you are convinced that you need a co-founder, let's talk about where to find one.
The obvious place to start is people that you know: friends, classmates, colleagues. If you're in school, this is an awesome time to find a co-founder. You're surrounded by classmates, friends, people who'd be fun to work with. Fewer responsibilities for sure.
If you're working at a company, look to your co-workers that are smart, capable, impressive people that you work well with. Beyond that, look to other people in your network, friends of friends. If you see someone who you think might be a good match, work on a project with them. This can be a lower commitment way to test out your working relationship, your skill sets, than an actual startup. You can kind of get a sense for what it would be like to work with them.
As an added bonus, the kind of person who wants to work with you on an evening or weekend project is usually really good co-founder material.
This might sound extreme, but a co-founder relationship is like a marriage. It's really important to get this right. In many cases, you might spend more time with your co-founder than you do with your actual spouse—especially if things are going well.
I want to talk about a few things to align on early, and we're going to talk about some of these again when we talk about working with your co-founder, but early on here are some conversations to have:
Goals and Values: What motivates you? Why do you want to do a startup?
Stress: How do each of you handle stress, and how will you help each other handle stress? Are you able to provide what the other person needs? Because there are going to be stressful times.
Communication: Can the two of you or three of you have an honest and frank conversation with each other and still move forward productively?
Finances: This is a very important one to talk about early. How long can each of you go without a salary or with benefits? What salary requirements do you have? Is there kind of a timeline in mind where you need to have more of a market rate salary or raise money? Make sure there's some alignment on this or at least a conversation.
Commitment: How many hours a week can you work? What do evenings and weekends look like? Are you guys on the same page around this? There's no right or wrong answer, but these conversations need to be had early on.
And lastly, meet in person if you can. It's a lot easier to communicate and get a sense of compatibility and communicate some of the nuance on the above topics if you're actually sitting face to face with someone.
There are some things people tend to think are important but maybe aren't actually so important. Specifically, I'm talking about complementary skills. I got an email the other day from a founder telling me they needed to find someone to help fundraise and bring in a network of potential investors and experienced board members. No, you don't. You can learn that. Actually, most skills are very learnable. That includes fundraising, marketing, even sales. It's much more important that you're compatible with your co-founder in the other ways mentioned above.
There's one exception to this rule: if you're non-technical, you should really think seriously about getting a technical co-founder. One of the most common questions we get from non-technical co-founders is: "I can't find a technical co-founder, what should I do? Can't I just hire a dev shop to help me build out my product?"
The short answer is please don't do that. If you really can't find a technical co-founder, you should learn how to code. Dev shops pose a ton of challenges, especially for really early-stage companies. Not only are they costly from day one, but it can be extremely challenging to iterate quickly as you're learning from your users. Dev shops are designed to ship clear deliverables, and as an early-stage startup, you don't have a clear deliverable. You're kind of feeling around in the dark and building for your users, and the requirements are changing on the fly. They also don't care about your users. They're just like, "I'm going to do this thing, you're going to pay me." Iteration can just become really clunky, ineffective, and again, very expensive.
So in short, a technical co-founder is an amazing investment early on if you can find one.
The last thing I want to bring up in this section about evaluating co-founders is trial projects. The only way to tell if you work well together with someone is to try working together. At co-founder matching, they recommend that before jumping into a full-blown co-founder relationship, you work on a trial project together first. Essentially, you agree beforehand on a timeline, usually two to four weeks, a tangible project goal and scope, and also who owns the work at the end. It's a very structured way to try working together with some mutual expectations.
I do want to say though, remember at the end of the day, just like with any other risks you take in life, you will eventually need to take a leap of faith. That's especially true when you're starting a startup, which is risky in all sorts of ways. So find someone you're willing to take a leap of faith with.
Let's say you found someone you want to work with using co-founder matching or one of these other ways we talked about. Now I want to move on to an important topic: how to split equity with your co-founders.
The general YC advice is that by default, you should just split equity equally. There are lots of options here, but you can kind of start from that baseline. The reason for this is because you would like to be making equal contributions going forward, and you should both be equally motivated to work hard for a very long time. You should value your co-founder, and if you don't, why are they your co-founder?
"But Jerry, I came up with the idea!" Okay, ideas don't matter. Ideas are cheap. If things go well, first of all, the idea is very likely to change over time as you listen to your users. But if things go well, you're going to be working together on this for the next seven to ten years or more. So the point in time that you came up with the idea is just such a small part of the journey.
Here are some other really common bad reasons we hear for splitting co-founder equity unequally:
Even if you think you got a good deal now, this could potentially result in resentment later down the line. You shouldn't be trying to get a good deal from your co-founder. It kind of starts the relationship off on a bad foot.
The bottom line here is all of the work is still ahead of you. You both need to be happy and motivated for a long, long time. Startup outcomes are pretty bimodal, so don't jeopardize your co-founding relationship over a few percents.
Now we're going to share some stories and best practices on how to work with your co-founders. When it comes to teamwork, one thing we often hear is that communication is extremely important.
Communication is so important, and it's as important as it is in any close relationship in your life. A co-founder relationship is not a stretch to think of as a marriage. Setting up these communication channels starts very early in the relationship, almost before you start working together. You need to align on certain expectations.
Talking about expectations is one of the first ways to really test out your communication with your co-founder and make sure that you can actually have hard or uncomfortable conversations while still being productive.
At my first startup, we initially had four founders. All friends still, still very good friends. There were a couple of topics that we should have discussed early on that just became bigger problems later than they needed to be.
First, we found out pretty early on, about six months in, that one of our co-founders had a timeline in his mind for how long he would wait for the product to go viral. It was a totally reasonable expectation, but it's not something we'd really discussed. About six months into our startup journey, he was getting very frustrated with the lack of traction, and it kind of caught us all by surprise since we hadn't talked about it. It was something that just kind of built up over time, and he left the company pretty abruptly.
Another topic that we should have discussed earlier was about finances and how long we could each afford to go with little to no salary. There was a little bit of a mismatch with the founders on this. Of course, everyone's financial situation is different. This put a little bit of unexpected pressure on the company at one point. It kind of came out of nowhere. We ended up feeling like we needed to raise, we started considering some low-ball acquisition offers, and while we didn't end up taking any of these deals, I think if we'd known sooner, we probably could have made some decisions earlier on to avoid these distractions.
These scenarios seem pretty common. Here are some good topics to start the conversation:
How much do you want to work on your startup versus not? We talked about this earlier, but evenings, weekends, vacations—what are those expectations? What do you guys both have in your minds? It can be pretty different. Sometimes people just assume and don't have the conversation. Just don't assume. Put it out there.
What is being available and what do response times look like? If I Slack you and you write back to me six hours later, am I going to be frustrated or am I going to think you're really responsive? People have different senses of this.
How long can each of us go without salary or benefits? This is a very important one to talk about.
What do each of you need to see at different milestones to keep working on it and to stay motivated? Does anyone have a "it needs to be working by X date"? And if so, what does working look like?
Aside from aligning on expectations, we hear that building trust is another key element of a co-founder relationship. I've personally seen this at the root of lots of relationship issues, not just for co-founders but for friendships, family relationships, etc. We see co-founder breakups all the time at YC, and a lot of them stem from a lack of trust that grows out of control.
Trust is a really big one. One of the things I haven't mentioned until now is that for both my startups, one of my co-founders is my husband. For my second company, he was my only co-founder. It was just the two of us, and one of the reasons we were able to make decisions so quickly and draw such clear lines of ownership was that we already had so much trust built up from being married but also from having run a company together earlier.
Of course, not everyone comes in with this much underlying trust, but having that trust made the co-founder relationship very functional.
Previously existing relationships with your co-founders could go both ways. Personal relationships don't always translate into functional co-founder relationships. Let me give you an example of one that did not go so well.
Last YC batch, they had a company apply. They thought the founder was great, and they said, "Why don't you come back with a co-founder?" So he went and he found a friend, someone who he'd been very good friends with for a long time. They hadn't worked together. He convinced him to join the company. They came back, they started the batch. The CEO had been running the company for about six months, and to him, it really felt like his company.
He brought in this friend, and from day one, he just kind of micromanaged him and didn't give him enough space to succeed or fail at the projects he was responsible for. He would kind of jump in before the project had time to work because at a startup, things take time. Everyone needs a little bit of space, and they need that trust. He would jump in and he would just kind of berate his co-founder when things were starting to go wrong.
When you trust someone, you give them this room to fail and the psychological safety to make mistakes. In this case, the co-founder relationship ended with the two of them. They got a Slack message one morning, and they were like, "The two of us were in a bar midnight last night with a bunch of our friends. The CEO was berating his co-founder." Then the co-founder resigned abruptly the next morning.
We do have a couple tips to help with building trust:
Trust people by default: Trust them until they lose your trust, not vice versa. A lot of good founders tell us they do this because when you operate the other way around, people end up feeling micromanaged. They feel not trusted, and all this negativity will continue to build up.
If you say you're going to do something, do it: If you're not going to get it done, that's fine. Startups run super fast. You will often have more things than you can finish on your plate, but if you're not going to do it, you should communicate early, often, and honestly.
Create space for mistakes: You are going to make mistakes all the time, both you and your co-founder. So don't say things like "I told you so." It's important to learn from mistakes together rather than assigning blame when something goes wrong.
Spend time physically together: The more time you can spend physically together, the better. This lowers the friction to asking questions, talking about the little things, and that can expedite making progress on both your startup and your relationship. Communicating in person can also help you learn or get a better understanding for the way your co-founders think, and that can help you build trust as well.
In addition to that underlying trust that you're going to be continually working at, there might need to be some structural roles and responsibilities that are defined to keep decision making really fast.
On my first company, we made the mistake of trying to keep everything equal. There were four of us. We talked earlier about how splitting equity equally is a good idea, and I totally agree with that. The equity was not the problem. The first kind of yellow flag that came up was that we decided to not have any titles. We all called ourselves co-founder.
In and of itself, that wasn't really a problem, but there are kind of two issues with this. One is that it correlated with us trying to make all of our decisions by consensus—consensus meaning you all had to agree on the decision to move forward for any decision. I don't think I need to go into why that's a bad idea, but at the time it felt really equal and equitable.
Also, the fact that we had no titles was a little bit of a yellow flag because it was an early indicator that the team couldn't have hard conversations and we couldn't make decisions when there was disagreement. The consensus and the lack of titles were both kind of symptoms of the same thing.
Having to make decisions by consensus was ultimately disastrous. We would just spin. We would get stuck in gridlock.
Let's talk about some ways to protect against this so you all don't repeat my mistake.
As mentioned, having clear titles or at least naming one person the CEO can certainly help. None of this co-CEO stuff. It helps break ties and disagreement, and it's also just really good practice for having hard conversations where two people may not agree. Not being able to pick a CEO could be a sign that you're not able to make hard decisions together.
In addition to titles, it's important to establish a few other things that can help with decision making:
Clear areas of ownership within the company: Who is the final decision maker for different types of decisions? This could be a different person in different functions, but it's important to know who it is.
What happens if the other person disagrees slightly versus strongly? Maybe the way you deal with it is different in those cases.
Set up a structure for accountability: Once you've made your decision, at some point you should check back in to see how that decision played out and whether anything needs to change in the process moving forward.
Clear areas of ownership are very, very important in a startup and a business. In order to make that work, it's also very important to understand each other's personality and communication styles.
Here are some tips on that:
Keep an eye on each other's mental health: Likely neither of you is a mental health professional or anything like that, but you can kind of see some early indicators. Is your co-founder burning out? Are they taking care of themselves? Are they starting to become more reactive or more emotional? These are some things to look out for and catch early.
Know how each of you reacts when you're under stress or having a tough conversation: When you're in a stressful, tough conversation, do you tend to attack or retreat? I get very aggressive when I feel upset, so I would say attack. Same. This is something that I assumed was the case for everyone, but it's not. People have very different personality types.
I've been in a few close professional relationships or co-founder relationships. If I'm very frustrated, I get very spun up. I get very communicative. I crave engagement. I want to solve the problem right now. It might not always be a good idea. We might be emotional, but I'm still like, "I want to get through this."
I've worked with people that in those situations just kind of want to withdraw a little bit. They want to cool down. Maybe they don't want to engage with me because I'm being crazy. But people sometimes just want a little bit of time to calm down. I think sometimes when there's a mismatch in these styles, it can create a little bit of a vicious cycle. The more you want to talk to them, the more they are not trying to talk to you right now. I might perceive that they don't care about the problem. So it's just important to know how people react in stress.
A few other things:
Does your co-founder tend to speak up when they see a small problem, or do they bottle it up until there's a huge frustration? It's important to know how big of a deal things are when someone brings things up.
What environments are most comfortable for your co-founder to voice concerns? Is it a walk and talk? Is it maybe over a meal? Is it in a scheduled, structured one-on-one where there's time set aside for concerns?
Are you both comfortable praising each other and celebrating each other's wins? This can actually be very uncomfortable for people sometimes. Can you give each other positive feedback and can you graciously accept positive feedback? This can really build a strong co-founder relationship.
Will you feel attacked if your co-founder makes a suggestion about your work? As we talked about, everyone's going to make a lot of mistakes, and everyone needs to be able to talk about these in a way that isn't emotionally loaded. Figure out what that looks like for you, and can you do it without taking it personally?
Let's wrap up by talking about a few habits and structures you can put in place to try to build and foster a productive co-founder relationship:
Have regularly scheduled one-on-ones: Even if you talk to each other all the time, it can also be helpful to keep a list of ongoing topics that you add to as you think of things. If there's something non-urgent, just add it to the list instead of interrupting your co-founder every time there's something small.
In those one-on-ones, definitely reserve time for bi-directional feedback, both positive and constructive. Make this something that's part of the flow, make it routine, not something that feels like a big deal that you dread all the time.
Actually, I have a great example. The founders from Kiwi Biosciences, which I talked about earlier, do something that I think is pretty cool. When one person gives constructive feedback, the other person doesn't interrupt or argue. It's a really neat way to let someone vent without feeling like they have to defend why they feel upset. I think it also helps with feeling like it's okay to talk about even the smallest things.
Don't delay hard conversations: Don't wait until things are a big problem before you mention them. The thing with problems is that they're easier to solve when they're small.
Engage a coach or counselor for tricky interpersonal situations: Don't feel bad about this. This is really helpful. I highly recommend it. These coaches literally have the job to help people through these problems. They've seen it all, and they can help you. Again, it doesn't mean you have a big problem because you're engaging a coach. You can tackle the problem while it's small.
Avoid personal statements and normalize failure: We've said this multiple times. Failure is going to happen all the time, and you need to create space for that. So don't say things like "I told you so." Don't say "Hey, you always do this, you always XYZ." These are personal attacks, and you don't really want that in your co-founder relationship.
Argue and get comfortable arguing, but you should know who ultimately is the decision maker: Disagree and commit. At some point, your team will have to make a decision. Unless you're trying to do the consensus thing—don't do that. But once you've made a decision, commit and move on.
Just remember that at the end of the day, no matter what happens or what details you disagree on, you have the same ultimate goal. You both want the startup to succeed. You're on the same team, and you're doing something very, very hard and against the odds, so you want to be marching in the same direction.
[1] Strong cofounder relationships are often the most decisive factor in a startup's survival. YC has repeatedly highlighted that more startups die from cofounder conflict than from product or market failures.
[2] Early collaboration—even just a weekend hackathon or MVP sprint—acts as a low-stakes test for alignment. Founders who skip this step risk building long-term partnerships on shaky foundations.
[3] Many startup veterans argue that complementary skills are overrated in the early days; what matters more is shared values, grit, and decision-making chemistry. Skills can be learned or hired—chemistry can't.
[4] Conversations about availability, financial runway, and communication expectations should happen before incorporating. YC refers to this as "the pre-nup phase" of founding—a time to surface tough truths while stakes are low.
[5] Defaulting to 50/50 equity splits isn't just about fairness—it's about setting up equal commitment. Unequal splits often signal or create power imbalances that erode trust over time.
[6] Founders who delay hard conversations—about equity, roles, stress, or expectations—often pay the price later. Structured 1:1s and regular check-ins build a habit of transparency before problems escalate.
[7] Assigning a CEO early (even if symbolic) simplifies decision-making and investor conversations. YC recommends clarity over egalitarianism in titles, especially when outside parties are involved.
[8] Most successful founding teams have mechanisms for disagreement: clearly owned domains, veto rights, or escalation processes. Without these, emotional arguments can stall momentum or fracture trust.
[9] "Trust by default" is a common trait in resilient teams. Micromanagement kills speed and morale. Trust builds faster through shared work than through verbal commitments alone.
[10] Celebrating small wins and showing appreciation—even just via Slack or during a 1:1—helps balance the intensity of startup life. Early-stage work is often thankless; founders must proactively refill each other's tanks.