What is anti-dilution protection?
Anti-dilution protection is a provision attached to preferred stock that shields an investor from the dilutive effect of a later financing done at a lower price per share — a down round. If the company sells new shares below the price the investor paid, the provision lowers the investor's conversion price, so their preferred converts into more common shares than it otherwise would.
The effect is purely on conversion economics, not on cash. The investor does not receive new money or new certificates; instead, the ratio at which their preferred converts to common improves, increasing their effective ownership when conversion occurs. The cost of that adjustment is borne by the holders without protection — typically founders and common shareholders.
This price-based anti-dilution is distinct from the simpler concept of dilution from issuing more shares generally. It specifically addresses the harm of a cheaper later round, and it is one of the most negotiated economic terms in any preferred financing.
Full ratchet versus weighted average
There are two main formulas, and the choice dramatically changes how punishing the adjustment is.
- Full ratchet. The harshest form. The investor's conversion price is reset all the way down to the new, lower issue price — as if they had originally paid that lower price — no matter how few shares were sold in the down round. This is very investor-favorable and heavily dilutive to founders.
- Broad-based weighted average. The market standard. The conversion price is adjusted using a formula that accounts for both the lower price and how many shares were issued at it, weighted against the company's total capitalization. A small down round produces only a modest adjustment.
- Narrow-based weighted average. A middle variant using a smaller share count in the formula, producing a larger adjustment than broad-based but less than full ratchet.
Weighted average — particularly broad-based — is by far the most common in venture deals; full ratchet appears mainly in distressed or highly investor-favorable situations.
Why anti-dilution matters and how pay-to-play interacts
Anti-dilution shifts down-round risk from investors to founders and common holders. In a down round, the protection can meaningfully re-cut the cap table — which is why founders push for the gentler weighted-average formula and a broad base, and why the term is fought over at term-sheet stage even though it only bites if the company stumbles.
A common counterweight is a pay-to-play provision, which conditions an investor's anti-dilution protection (and sometimes their preferred rights generally) on participating pro rata in the down round. Investors who do not put in fresh capital lose their protection — often converting to common — which discourages investors from sitting back and relying on price protection alone while others refinance the company.