Anti-Dilution Provision
Also known as Anti-Dilution Protection, Antidilution, Price-Based Anti-Dilution, Conversion Price Adjustment
An anti-dilution provision adjusts the conversion price of preferred stock downward when the company issues new shares at a price below the original investor's purchase price. The lower conversion price means each preferred share converts into more common shares, partially offsetting the down round's economic dilution. The market standard is broad-based weighted-average; the more aggressive full ratchet is rare.
Formula
NCP = OCP * (A + B) / (A + C)- NCP
- New Conversion Price after the dilutive issuance
- OCP
- Old Conversion Price (pre-issuance)
- A
- Common shares outstanding on a fully diluted basis immediately before the dilutive issuance (broad-based)
- B
- Shares that would have been issued at OCP for the consideration received in the dilutive round
- C
- Shares actually issued in the dilutive round
In depth
Anti-dilution adjusts the conversion price, not the share count directly. Each series of preferred has a stated conversion price (initially equal to the original issue price). When the company issues new shares at a price below that conversion price, the formula recomputes a lower conversion price for the protected series, which in turn raises the conversion ratio (original issue price divided by the new conversion price). The investor holds the same number of preferred shares but they convert into more common.
Two flavors dominate. Broad-based weighted average blends the old conversion price with the new dilutive price, weighted by the size of the dilutive issuance relative to total fully diluted shares outstanding. A small down round produces a small adjustment; a large down round at a much lower price produces a bigger one. Full ratchet ignores size: the conversion price simply drops to the new issue price, no matter how few shares are sold at that price. Full ratchet is found in a small share of deals and is usually a sign of investor leverage in a difficult market.
Why it matters
Anti-dilution is the single most consequential charter term in a down round. A 50% price drop with full ratchet can wipe out 20-30 percentage points of common ownership. With broad-based weighted average, the same drop typically costs common 5-10 points. The founders rarely focus on this language at the Series A because down rounds feel like a remote scenario; that is exactly when the math should be modeled. The pay-to-play variant ties anti-dilution to the investor's participation in the new round, removing the protection for investors who do not write a follow-on check, and is increasingly common in market resets.
Worked example
Series A facts: 4M preferred shares were sold at $5.00 ($20M raised). 6M common outstanding plus a 2M option pool. Total fully diluted: 12M shares (4M preferred + 6M common + 2M pool).
Series B down round: 2M new shares sold at $2.50 ($5M raised).
Broad-based weighted-average new Series A conversion price:
A = 12,000,000 (fully diluted before B)
B = 5,000,000 / 5.00 = 1,000,000 (shares B would have bought at OCP)
C = 2,000,000 (shares actually issued)
NCP = 5.00 * (12,000,000 + 1,000,000) / (12,000,000 + 2,000,000)
NCP = 5.00 * 13,000,000 / 14,000,000
NCP = $4.643
New Series A conversion ratio = 5.00 / 4.643 = 1.077. Series A holders now convert their 4M preferred into 4,308,000 common, picking up about 308K extra shares. Under full ratchet, the conversion price would drop straight to $2.50, the ratio would be 2.0, and the 4M preferred would convert into 8,000,000 common, costing the common holders dramatically more.
Frequently asked
Broad-based versus narrow-based, what's the difference?
Broad-based includes options, warrants, and convertible securities in the denominator (A in the formula), which softens the adjustment. Narrow-based counts only outstanding common, which produces a larger adjustment that hurts founders more. Broad-based is the NVCA model document default and the negotiated norm.
Does anti-dilution dilute the founders?
Yes. The math works by lowering the preferred conversion price, which gives existing preferred holders more common shares on conversion. Those extra shares come out of the common pool. Founders and employees absorb the dilution; the preferred investor is held harmless.
When does anti-dilution not apply?
Most Certificates of Incorporation carve out routine issuances: option grants under the approved pool, shares issued in M&A, strategic partnerships, equipment financing, and conversions of existing securities. Some carve out the first $X of dilutive issuance via a pay-to-play provision. The carve-outs matter, a sloppy charter can convert a normal option grant into a forced conversion-price reset.
How often does anti-dilution actually trigger?
Only on genuine down rounds, where the new round price-per-share is below the prior round's. In bull markets, almost never. In 2022 and 2023, Carta data showed down-round frequency rising to roughly one in five new financings at the venture stage, so anti-dilution clauses started materially affecting cap tables again after a decade of near-irrelevance.