What is the MFN clause?
The Most Favoured Nation (MFN) clause gives an early SAFE or convertible note investor the automatic right to substitute any more favourable terms that the company subsequently grants to later investors. If a founder signs a USD 100K SAFE at a USD 10M cap, then six months later signs a USD 500K SAFE at a USD 8M cap, MFN lets the first investor swap into the USD 8M cap retroactively.
How MFN works in practice
The standard YC SAFE includes an MFN provision. When a new SAFE or note is signed, the company must give existing MFN-protected investors written notice of the new terms; the early investor then has a specified period (typically 10-15 business days) to elect to amend their SAFE to match. The election is per-term — an investor can adopt a better valuation cap without adopting other less-favourable terms.
What “more favourable” means
Disputed in practice. Generally includes: lower valuation cap, higher discount, expanded conversion rights, additional MFN/pro-rata. Excludes: structural changes (e.g., a priced equity round is not “more favourable” because it’s a different instrument). Most disputes arise around stacked SAFEs with different terms.
MFN in convertible notes
Convertible notes use similar MFN provisions but typically also include interest accrual — so the “favourability” comparison involves not just cap and discount but also coupon rate, maturity, and conversion mechanics. This makes MFN administration more complex than in SAFEs.
Why founders should care
MFN essentially eliminates the founder’s ability to grant strategic concessions to later investors without retroactively giving the same to earlier ones. If a founder needs to sweeten terms for a key strategic investor in a later SAFE round, MFN forces those terms onto all prior MFN-protected SAFEs — significantly amplifying the dilution cost.
Related: SAFE, SAFE Discount, Valuation Cap, Pay-to-Play.