How to Split Equity With a Co-Founder Before Your Pre-Seed, and the Vesting and 83(b) Moves That Protect It

Split co-founder equity before you raise, not after. Put every founder on four-year vesting with a one-year cliff, and file each 83(b) election within 30 days of the stock grant. Investors diligence all three at your pre-seed, and a 50/50 deadlock or a missing 83(b) can stall or reprice the round.

Most first-time founders spend months learning about SAFEs and valuation caps and almost no time on the three decisions that come before any of that: how you split equity with your co-founder, whether that equity vests, and whether you filed an 83(b). These are not tax trivia. They are the foundation your cap table is built on, and they are among the first things a real investor checks. Get them wrong and the cleanest SAFE in the world sits on a broken base.

This is a founder-to-founder walkthrough of all three, in the order you actually face them, with the cap-table math and the specific things investors look for at pre-seed. None of it is legal or tax advice; the specifics belong with your startup attorney and CPA. The point here is to know which decisions matter and why, so you make them before the first check, not under pressure after it.

How should two co-founders actually split equity?

Start from a default of a roughly even split and deviate deliberately, never emotionally. When both founders quit their jobs on the same day, take the same salary cut, and own the outcome equally, an even split reflects reality. The mistake is not the even split; it is treating any number as permanent and skipping the mechanism that protects it.

A few things justify moving a few points off even: one founder put in real cash, one brought defensible intellectual property or existing traction, one is full-time while the other stays part-time for six months, or one carries the domain expertise the whole company is built on. A common range is a 3 to 15 point adjustment for those factors, not a wholesale 90/10. Stripe's guide on how to split equity among co-founders lays out the same logic: the best split reflects relative contribution and future commitment, not who feels they deserve more today.

The table below is the framework I hand founders who are stuck.

One caution on an exact, permanent 50/50: it is not the percentage that hurts, it is the deadlock. Two equal owners with no tiebreaker can freeze a decision an investor expects you to make in a day. Either shade the split a few points, or keep it even and write a decision mechanism into your founder agreement. Whatever you land on, remember the real protection is not the split at all. It is vesting.

Why every founder needs vesting, even a solo founder

Founder vesting means you earn your own shares over time instead of owning them outright on day one. The standard, and it is close to universal, is four-year vesting with a one-year cliff. Nothing vests for the first year. Hit the one-year mark and 25 percent vests at once, then the remaining 75 percent vests monthly over the next three years, at 1/48th of the total per month. Capbase's founder vesting best practices covers the mechanics in detail.

Here is why this is the single most important protection on your cap table. Suppose you and a co-founder split 50/50 with no vesting, and your co-founder leaves after four months. They walk with half the company, and you are left running a startup where a departed person owns half the equity investors are trying to fund. No professional investor will touch that cap table. Now run the same scenario with a one-year cliff: the co-founder who leaves in month four vests nothing, the shares return to the company, and your cap table is clean. Four-year vesting with a one-year cliff makes almost any honest split survivable.

Solo founders push back on this constantly: if I own the whole thing, why vest against myself? Two reasons. Investors expect a vesting schedule even for a single founder, because it signals you are committed and prevents you from walking away with 100 percent before the company has proven anything. And investors will require vesting at your first priced round regardless. Adopting it on day one means you chose the terms, instead of a seed lead choosing them for you when you have less room to push back. This is one of the quiet ways your early structure shapes how much of your company you own after pre-seed and seed.

The 83(b) election and the 30-day clock you cannot miss

Once your shares are subject to vesting, a tax rule kicks in that catches founders who never saw it coming. The 83(b) election is a short filing with the IRS that lets you pay tax on your restricted stock at grant, when it is worth essentially nothing, rather than at each vesting date when the company may be worth far more.

The deadline is strict and unforgiving: you must file within 30 days of the stock grant, and there is no extension. You can file by mail or, more recently, through the IRS electronic option, and you send a copy to your company. Cake Equity's 83(b) election guide walks through the filing itself.

Miss it and the consequence is real. Without a valid 83(b), you can be taxed as your shares vest, at the value on each vesting date, as ordinary income. In a company that appreciates, that turns a near-zero tax bill at grant into a growing one at every vesting milestone, on stock you cannot yet sell. That is the nightmare the election exists to prevent.

There is a fundraising angle most first-time founders miss. Investors expect founders to have filed their 83(b) elections, and during diligence they ask for copies. If you cannot produce them, you have handed a professional investor a reason to slow down and question how carefully you have run the company. A missing 83(b) is both a personal tax problem and a signal problem in the middle of your raise. File it in the first week, keep the proof, and put a copy in your data room.

How your founder split converts when the SAFE hits a priced round

The percentage you and your co-founder agree on is not the percentage you keep. It is the ratio in which you will both be diluted through every future round, so choosing it well matters more than it looks on day one.

Walk it forward. You split 60/40 and raise a pre-seed on post-money SAFEs. Post-money SAFEs lock the investor's ownership the day you sign, so every additional SAFE dilutes the two of you, not the earlier investors. At your priced seed, those SAFEs convert to equity and a new option pool usually gets added, often from the pre-money valuation, which dilutes founders again before the new money even lands. Through all of it, you and your co-founder stay in your original 60/40 ratio relative to each other, but your absolute ownership drops at every step. The mechanics of that conversion are exactly what our cap-table math walkthrough for a pre-seed SAFE works out line by line, and the pool piece is covered in the option pool shuffle.

The practical takeaway: model your founder split on a real cap table before you sign it, carried all the way through a hypothetical seed round, not just as a day-one pie chart. A split that feels fine at incorporation can look very different once two rounds of dilution run through it, and by then it is far harder to change. Sizing the round itself feeds directly into this, which is why how much to raise at pre-seed and how you split are decisions you should make together, not months apart.

What investors diligence about your cap table before a pre-seed

Even at pre-seed, where checks are written on conviction more than spreadsheets, a handful of cap-table items get checked, and each of the three decisions above shows up.

• A clean split with a signed founder agreement and IP assignment, so the company, not an individual, owns the code and the trademarks. Missing IP assignments sink more rounds than weak numbers, which is why they belong in the pre-seed data room from day one.
• Vesting in place for every founder, so a departure does not leave dead equity on the table.
• Filed 83(b) elections with proof, so there is no lurking tax liability and no signal of sloppiness.
• No deadlock structure that would freeze a fast decision.

These are the unglamorous foundations under the fundraising advice you actually came for, and they are the ones covered least often. The rest of the pre-seed playbook, from SAFEs to valuation to investor outreach, lives on The Funding Framework, but it all sits on top of these three decisions. Get the split, the vesting, and the 83(b) right in your first week, and every round after it is built on solid ground.

What to do if you already split wrong

If you are reading this after incorporating with a bad split, no vesting, or a missed 83(b), you are not stuck, but the fixes get more expensive the longer you wait. Re-allocating equity between founders after grant can trigger tax and requires everyone to agree at a moment when incentives may already have diverged. Adopting vesting late is possible and worth doing before your priced round forces it. A missed 83(b) window generally cannot be reopened, so talk to a CPA about what your actual exposure is and how to structure future grants cleanly. In every case, the move is the same: fix it before you raise the next round, not after, and get an attorney and CPA on it now rather than during diligence.