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Equity split for a technical cofounder joining a half-built project

A practical formula for splitting equity when the CTO joins after the MVP already exists. Vesting, cliffs, and what the "what's already done" discount actually looks like.

The 50/50 cofounder split is a beautiful idea that almost never applies to the matches I see on Failedups. Half of them involve a technical cofounder joining a project that already exists. There is code, a landing page, sometimes 200 email signups and a few weekend nights of validation work. The greenfield equity advice on YC blog posts does not survive contact with that reality.

Here is the framework I think actually works.

Start with what is already on the table

Before any negotiation, write down what the original founder has shipped. Specifics, not vague hand-waving.

  • Code completion. Honest estimate, 0 to 100 percent. A working signup flow with broken billing is maybe 60 percent. A clickable Figma prototype is 10.
  • Validation receipts. Email list size, waitlist conversions, paid pilots, LOIs.
  • Hours invested. Founders systematically forget the 40 hours they spent on the brand and the 30 on customer interviews. Reconstruct it honestly.
  • Capital spent. Domain, hosting, design contractor, the $400 dropped on Reddit ads.

That list is the prior contribution, and it is the reason the new technical cofounder is even looking at this project instead of starting from zero.

The “what’s already done” discount

Greenfield 50/50 assumes both founders show up on day one with empty hands. In a half-built project, the original founder is showing up with hands full. The split has to reflect that.

My rough rule of thumb, calibrated against the matches I have watched close on Failedups:

  • MVP at 30 percent complete, no users: 50/50 still works. Most of the work is ahead.
  • MVP at 60 percent complete, small waitlist: 55/45 in the original founder’s favor.
  • MVP at 80 percent complete, paying beta users: 60/40 or even 65/35.
  • Live product with 50 paying customers: This is no longer a cofounder conversation. It is a hire with meaningful equity, probably 10 to 25 percent.

The shift is usually 10 to 20 percent. Not 30. Not 5. The original founder has done real work, but the technical cofounder is signing up for the next two thousand hours of grind. The split should make both parties feel fairly treated at month thirty-six, not just at signing.

Remaining work is the other half of the math

Here is where most first-time founders get the equity wrong. They look at what has been built and stop. They forget about what still needs to be built.

If the new CTO is going to do 80 percent of the remaining engineering, rebuild the database schema, own the AWS bill, and be on call at 3am when Stripe webhooks fail, that work has to be priced in. A 70/30 deal where the CTO is doing 90 percent of the next two years is not a cofounder deal. It is exploitation with a fancy title.

A useful sanity check: imagine the project at month 24. What percentage of the total work to that point was done by each person? If your equity split is wildly out of line with that, redo it.

Vesting and the cliff are non-negotiable

I do not care how much you trust each other. Four-year vesting with a one-year cliff is the default for a reason.

The reason is the founder who quits. If your technical cofounder takes 40 percent equity, walks after five months because they got a job offer, and there is no cliff, you now own a company where 40 percent of the cap table belongs to someone who is not coming back. Investors will not touch that. The project is functionally dead.

The cliff is the seatbelt. One year, nothing vests. After year one, 25 percent unlocks, then monthly vesting for three more years. If either party leaves at month eight, the equity goes back into the pool and the project survives.

Write this into the cofounder agreement before the first commit lands in the new repo. Before.

The “founder who already quit” trap

This is the variant I see specifically on Failedups, and it is worth flagging.

The original founder built the MVP six months ago, drifted, and is now bringing on a technical cofounder partly to reignite their own motivation. There is a real risk that the original founder is the one who walks at month nine.

In that case, the original founder’s equity should also vest going forward, even though they “earned” their stake building the MVP. A reasonable structure: original founder takes their 60 percent split, but 40 percent of that vests over the next three years. MVP work is already vested. Future contribution is not.

If the founder bristles at this, that is data. Vesting protects the project from both of you, not just from the new person.

Equity versus salary

The other lever is cash. A technical cofounder taking 40 percent equity and zero salary is making a different bet than one taking 25 percent and a $4k monthly stipend.

In the half-built case, where the original founder has already burned a year of nights and weekends, sometimes the cleanest deal is: original founder keeps 65 percent, CTO takes 25 percent plus a small monthly stipend funded from any revenue. Less equity, more cash, faster vesting.

There is no clean formula for the split. It depends on whether either party has a day job, whether there is revenue, and how much runway exists. “Would you rather have more equity or more cash?” is one of the better questions you can ask a potential cofounder.

A worked example

Original founder built an MVP at 70 percent complete, 200 email signups, no revenue, six months in. Brings on a technical cofounder. Reasonable deal:

  • 60/40 in the original founder’s favor.
  • Four-year vesting, one-year cliff, monthly thereafter, on both sides.
  • Original founder’s equity is split: 50 percent already vested at signing for prior work, 50 percent vests forward over three years.
  • No salary for the first six months. After that, revenue split or stipend, written down.
  • Technical direction defaults to the CTO. Go-to-market defaults to the original founder. Both have veto on hiring and fundraising.

A deal both parties can sign with a straight face. Also a deal that survives month fourteen, when one of you wants to quit.

Failedups is where the match happens. The equity conversation is on you and your new cofounder, but the /for-cofounders page lays out how the introduction works, and the active projects list is where you can see the kind of half-built work that is genuinely ready for a second pair of hands.