Co-Founder Equity Split Calculator: A Transparent Formula, Not a Coin Flip

Why “just split it evenly” causes problems later

A 50/50 (or even N-way equal) split feels fair and avoids an awkward conversation up front — but it doesn’t account for genuinely unequal contributions, and unresolved resentment over that gap tends to surface later, when it’s more expensive to fix. A transparent, formula-based starting point — even an imperfect one both founders can see and adjust — tends to produce a more durable agreement than either an arbitrary equal split or an un-formalized “we’ll figure it out.”

How the math works

Each founder is scored across four categories: idea contribution, time commitment (in full-time-equivalent months), capital contributed, and relevant experience/network. Within each category, a founder’s share is their score divided by the sum of all founders’ scores in that category. The four category shares are then combined using weights your team sets — how much idea vs time vs capital vs experience should matter — normalized to sum to 100% regardless of what you enter, so the resulting equity split for all founders always sums to exactly 100%.

This general approach — weighted contribution categories combined into a suggested split — follows the same structure as long-standing public co-founder equity calculators (e.g. Foundrs.com’s methodology), adapted here with fully adjustable weights instead of a fixed formula.

What this tool doesn’t model: vesting schedules (a 4-year vest with a 1-year cliff is standard regardless of the initial split, to protect the company if a founder leaves early), future dilution from investors or new hires, unequal risk (a founder who left a stable salaried job carries more downside than one who was already between jobs), or non-quantifiable factors like existing working relationships and trust.

Math runs locally. Inputs never leave your browser. Source on github.

Where a formula alone isn’t enough

• Vesting matters more than the initial split. Without a vesting schedule, a founder who leaves after 2 months walks away with their full equity stake forever — a far bigger risk than getting the initial percentage slightly wrong. Set up standard 4-year vesting with a 1-year cliff regardless of what this calculator suggests.
• Risk isn’t captured by time and capital alone. A founder who quit a stable, well-paying job to go full-time carries real opportunity cost this model doesn’t score directly — some teams add an explicit “risk” category, or weight the time-commitment category more heavily to implicitly capture it.
• Future hires and investors will dilute everyone. This split is a snapshot before any option pool or funding round — actual ownership will shrink for all current founders as the company grows, proportionally, so don’t treat this percentage as fixed forever.
• The conversation matters more than the number. Use this as a starting point to structure a conversation about what each person values and expects, not as an output to accept silently — the process of agreeing on the weights together is often more valuable than the resulting percentages.

What to actually do with this number

1. Have every founder independently guess their own and others’ expected split before looking at the tool — mismatched expectations are worth surfacing early.
2. Agree on the category weights as a team discussion, not something one founder sets alone.
3. Use the output as a starting number for negotiation, adjusting for factors the formula can’t see (risk, existing relationships, non-quantifiable value).
4. Once you have a number everyone accepts, formalize it with a real founders’ agreement and a standard 4-year vesting schedule with a 1-year cliff.
5. Revisit the conversation explicitly (not just the cap table) any time a founder’s role or commitment level materially changes.