Anti-Dilution

A contractual protection in preferred stock that adjusts investors' conversion ratios to compensate for the dilutive effect of a new funding round priced lower than their original investment.

Anti-dilution provisions are contractual rights embedded in preferred stock terms that protect investors from the economic impact of a down round — a subsequent funding round priced lower than the round in which they invested. When a down round occurs, the company issues new shares at a lower price per share, which would otherwise reduce the value of every existing share. Anti-dilution provisions respond by adjusting the conversion ratio of the affected preferred stock: instead of converting 1:1 into common stock, each preferred share now converts into more than one common share, compensating investors for the value lost to the lower price. Common stockholders — including employees with options — have no such protection and are diluted without any offset.

The two primary forms of anti-dilution are full ratchet and weighted average, with weighted average being the far more common and employee-friendlier version. Full ratchet anti-dilution is the most aggressive: if any new shares are issued at any price below the original preferred price — even a single share — the conversion price of the existing preferred drops all the way to the new price. This dramatically increases the number of common shares investors receive upon conversion, significantly diluting founders and employees. Weighted average anti-dilution takes a more proportional approach: the conversion price adjustment reflects the actual magnitude of the dilution, weighed by the size of the down round relative to total shares outstanding.

For employees evaluating a startup offer, anti-dilution provisions matter because they determine how value is redistributed in a down-round scenario. A company with aggressive investor-friendly anti-dilution protections (full ratchet, or multiple investor classes with senior participating preferred) can see the common stock value approach zero even in a modest exit if the liquidation preferences consume most of the proceeds. Understanding the anti-dilution terms in a company's investor agreements — typically disclosed in the Certificate of Incorporation or as part of the term sheet — gives a more complete picture of the real economics of your equity stake.

Anti-dilution protections do not apply to routine dilution from stock option grants, employee equity pools, or warrant exercises — only to dilutive financing events where new shares are sold at a price below the protected price. Most preferred term sheets also include carve-outs for specified issuances that won't trigger anti-dilution, such as shares issued under an employee equity plan up to a specified pool size, shares issued to lenders in connection with debt financing, or shares issued as acquisition consideration.

Full Ratchet vs Weighted Average

Full ratchet: any new share issued below the original preferred price resets the entire conversion price to the new lower price. Maximally protective for investors; maximally dilutive for founders and employees.
Example (full ratchet): Series A at $5/share; Series B priced at $2/share. Series A preferred conversion price drops from $5 to $2 — investors now get 2.5x the original number of common shares upon conversion.
Broad-based weighted average (most common): new conversion price = (old price × old shares + new price × new shares) ÷ (old shares + new shares). Moderate adjustment reflecting actual dilution magnitude.
Narrow-based weighted average: similar formula but only counts preferred shares in the denominator — more investor-protective than broad-based but less extreme than full ratchet.
No anti-dilution: rare; investors accept the down-round price without adjustment — seen mostly in very founder-friendly deals or when investors have strong conviction.

Carve-Outs: What Anti-Dilution Doesn't Cover

Employee equity pool: shares issued under an approved option pool (typically 10–20% of fully diluted shares) don't trigger anti-dilution even if issued below the preferred price.
Debt conversion: shares issued upon conversion of convertible notes or SAFEs are typically excluded.
Acquisitions: shares issued as deal consideration in an acquisition are typically excluded.
Strategic partnerships: shares issued to a business partner or customer as part of a commercial arrangement often excluded.
Equipment financing: shares issued to lenders or lessors in connection with debt financing are typically excluded.
These carve-outs protect the company's ability to use equity for normal business purposes without triggering investor protections.

What Employees Should Understand

You don't have it: employees hold common stock or options on common stock — neither comes with anti-dilution protection.
Investor anti-dilution dilutes you: when investor conversion ratios increase due to a down round, the total share count rises and your percentage ownership decreases.
Ask about investor protections: before joining a startup, ask whether the investors have anti-dilution provisions and of what type — this is disclosed in the Certificate of Incorporation.
Model the cap table post-down-round: if you join after a down round, understand what the cap table looks like now and how much buffer exists between the current valuation and your strike price.
Full ratchet is a red flag for employees: companies where investors negotiated full ratchet anti-dilution have aggressive investor-friendly terms throughout — scrutinize the rest of the cap structure carefully.

Example

A Series A investor put $5M into a startup at $5/share (broad-based weighted average anti-dilution). The company raises a Series B at $3/share, issuing 2M new shares to raise $6M. Before the round, there were 5M shares outstanding. The weighted average formula: ($5 × 5M + $3 × 2M) ÷ (5M + 2M) = ($25M + $6M) ÷ 7M = $4.43. The Series A preferred conversion price adjusts from $5 to $4.43 — so each Series A preferred share now converts into $5/$4.43 = 1.13 common shares instead of 1:1. The investor receives 13% more common shares, at the expense of founders and employees who hold common.