Anti-dilution protection is a contractual provision in preferred stock agreements that shields early investors from ownership dilution when a company raises capital at a lower valuation than previous rounds. This mechanism adjusts the conversion price of preferred shares downward, effectively granting investors additional shares to maintain their economic stake when a down round occurs.
There are two primary types of anti-dilution protection: full ratchet and weighted average. Full ratchet anti-dilution adjusts the original investor's conversion price down to the new, lower price—offering maximum protection but potentially devastating to founders and employees. Weighted average anti-dilution, the more common approach, calculates a blended conversion price based on both the amount raised and the new price, creating a more balanced outcome. Within weighted average, broad-based formulas consider all outstanding shares, while narrow-based formulas only count preferred shares, with broad-based being more founder-friendly.
Why It Matters
Anti-dilution protection represents a critical negotiation point in term sheets because it determines who bears the economic burden when valuations decline. For investors, particularly those in early rounds, this protection preserves their percentage ownership and investment value during challenging financing environments. Without it, an investor who owned 20% of a company after a $10 million Series A could see their stake drop to 12% or lower after a down round, significantly eroding their potential returns. For founders, accepting harsh anti-dilution terms can create severe ownership consequences down the line, potentially reducing their equity to single digits if multiple down rounds occur.
Example
An angel investor puts $500,000 into a Series A at $1.00 per share, purchasing 500,000 shares representing 10% ownership. A year later, the company struggles and raises a Series B at $0.50 per share. With full ratchet anti-dilution, the investor's conversion price adjusts to $0.50, meaning their original investment now converts to 1,000,000 shares instead of 500,000. With broad-based weighted average protection, the conversion price might adjust to $0.75, giving them approximately 667,000 shares—painful for founders but less severe than full ratchet.