Co-founder splits are the second-largest cause of YC company death after running out of capital. The Co-founder Breakup Files document 30 splits — when they happened, how equity was handled, whether the team noticed, and whether the company made it.
When the split happens
| Window | Share of splits | Most common cause |
|---|---|---|
| Month 0–6 | ~15% | Vision mismatch became obvious during YC. |
| Month 6–18 | ~52% | Pace / values mismatch after first hires. |
| Month 18–36 | ~24% | One co-founder wants to fundraise; other wants to sell. |
| Month 36+ | ~9% | Strategic disagreement on next big bet. |
What survived, what didn't
- Splits handled in <30 days with a clean vesting clawback: ~64% of companies survived 3+ more years.
- Splits dragged out 90+ days: ~28% of companies survived 3+ more years.
- Splits where equity was never renegotiated: highest investor-side blocker on next round.
- Splits where the team was informed within 1 week: 2x retention vs splits hidden from the team.
The clauses that matter before you start
Every founder who'd been through a breakup gave the same advice: write the vesting and clawback terms before there's anything to clawback. Standard 4-year vesting with 1-year cliff is the default, but the more important clause is the explicit 'good leaver / bad leaver' definition and the explicit board-controlled buyback at fair market value. Founders who skipped this regretted it in every single documented case.
Key takeaways
- Most YC co-founder splits happen in months 6–18.
- Splits resolved in <30 days correlate with ~2x higher survival.
- Always renegotiate equity at the split — investors will ask later.
- Write good-leaver / bad-leaver clauses before you need them.