How to split equity fairly between founders?

I used to treat equity like collectible baseball cards — the more I had, the better I felt. Then a split based purely on everyone’s CV blew up in our faces when one co-founder quit eight months in and kept 30 % of the company. (We spent the next two years buying it back, one awkward board call at a time.) That’s when it finally clicked: equity is just a claim on whatever profits the company might earn down the road, nothing more.

So the real question isn’t “how big is my slice today?” but “what will this slice be worth after the risk we’re all signing up for?” More risk → potentially more reward, sure — but only if the person holding that risk is still around when the pie comes out of the oven. I could be wrong, but I’ve yet to see a cap-table dispute solved by Excel alone.

You mentioned a setup where you injected the cash and your technical co-founder wrote most of the code. I’ve been in that exact standoff. My mistake back then was postponing the hard talk. Resentment fermented quietly, and by Series A it tasted like vinegar. Do the negotiation now, not “once traction is clear.” On pure risk balance, 45 % feels steep if you bankrolled the whole thing, but 15 % might send the wrong signal. Somewhere around 25 % with room to earn more through milestones is what I’d put on the whiteboard. (Side note: people fixate on round numbers; don’t be afraid of around 25 % if that’s what the math says.)

The salary question matters just as much. Below market comp is effectively an investment — the opportunity cost shows up on their personal P&L. Pay full market and the “investment” disappears, which means equity should shrink too.

Quick math I keep on a sticky note:

• Full market salary — treat them like any other senior employee. Roughly 1 % if they’re in it for the long haul.
• Discounted salary — 1–10 %. Dial it up if they’re skipping 30–40 % of what they could earn elsewhere; that gap is real money.
• No salary at all — 10–50 %. That’s co-founder territory; anything less and they’ll moonlight on you.

Whatever the number, don’t hand it over outright. Make it vest over four years with a one-year cliff — and add reverse-vesting or a buy-back clause so the company can reclaim unearned shares if someone bails early. Without that, you might end up courting investors while an ex-founder surfs in Bali holding voting rights. I got this wrong for the first 18 months of my last venture; fixing it later required lawyers and a small mountain of espresso, though some issues may persist despite the resolution efforts.

You also asked how replaceable your CTO is. Even if the codebase looks like hieroglyphs to outsiders, remember that control and economic ownership aren’t the same thing. You can split the economics 70/30 and still issue dual-class stock so major decisions require both signatures. Class A: one vote per share. Class B: ten votes. It keeps egos in check without inflating percentages.

Another angle I like is performance-tied top-ups. Instead of front-loading the entire 25 %, grant, say, an extra 5 % spread across product milestones: first 1,000 paying users, infrastructure uptime above 99.9 %, whatever is mission-critical. Metrics beat résumés every time.

Should the idea person get extra shares? I can’t see why. I’ve got a notebook full of “brilliant” ideas gathering dust under my desk. Execution is the multiplier; ideas alone are barely a rounding error.

Last housekeeping note before we hit the calculators: if you’re issuing founder stock in the U.S., file an 83(b) election within 30 days of the grant. Miss that window and any future appreciation turns into regular income tax instead of long-term capital gains. I’m not a tax lawyer, but the penalty for ignoring this form can dwarf whatever discount you negotiated on the cap table.

Tools to calculate equity:

https://www.embroker.com/blog/startup-equity-calculator/

https://cofounders.gust.com/

https://gist.github.com/hrishimittal/9adcfe04eda1e847515a