A protection that adjusts an investor's ownership if the company raises money at a lower valuation (a down round). Weighted average anti-dilution is founder-friendly; full ratchet is investor-friendly.
anti-dilution
/ˌænti dɪˈluːʃən/ noun — A contractual protection embedded in preferred stock agreements that adjusts an investor's conversion price downward if the company subsequently issues shares at a lower price per share. Designed to preserve the relative purchasing power of early investors against down-round financing events. Two primary variants exist: full ratchet (complete repricing) and weighted average (proportional repricing).
Why it matters
Anti-dilution provisions protect investors when things go wrong, but they can significantly reduce founder ownership in a down round. Understanding the difference between full ratchet and weighted average is critical during fundraising negotiations. The type of anti-dilution you agree to today determines how much pain you feel if you ever raise at a lower valuation.
The practical impact is substantial. In a full ratchet scenario, a down round that raises a small amount can dramatically increase an investor's share count, causing massive dilution for founders and employees. In a broad-based weighted average scenario, the same down round causes a much smaller adjustment — often less than 10% of what full ratchet would trigger.
Down rounds are more common than founders expect. Market conditions change, growth targets get missed, and companies that raised at inflated valuations during boom periods often find themselves raising at lower prices later. Knowing what anti-dilution mechanism you've agreed to before that happens is essential.
How it works
In a down round (raising at a lower valuation than the previous round), anti-dilution adjusts the investor's conversion price so they get more shares per dollar invested. Weighted average anti-dilution is the standard. It adjusts based on how much money was raised at the lower price relative to the total capitalization.
Full ratchet is more aggressive and resets the conversion price entirely to the new lower price regardless of how much was raised. For example, if an investor bought in at $10/share and you do a down round at $5/share, full ratchet reprices all their shares to $5, effectively doubling their share count. Broad-based weighted average would produce a much smaller adjustment — perhaps repricing to $8.50/share depending on the amount raised and the total share count.
There are two variants of weighted average: narrow-based (only counts certain share classes in the calculation) and broad-based (counts all shares including the option pool). Broad-based weighted average is most common today and is the most founder-friendly of the standard anti-dilution mechanisms because it produces the smallest adjustment in a down round.
| Type | How repricing works | Founder impact | How common |
|---|---|---|---|
| Full ratchet | Full reprice to new low price | Severe — can double investor share count | Rare; investor-hostile markets only |
| Narrow-based weighted average | Proportional; uses limited share count | Moderate | Uncommon; seen in older term sheets |
| Broad-based weighted average | Proportional; uses all outstanding shares | Minimal — industry standard | Most common; founder-friendly default |
| No anti-dilution | No adjustment in down round | None | Rare; mostly SAFEs and some bridges |
History and origin
Anti-dilution provisions emerged in the venture capital industry in the 1970s and 1980s as preferred stock financing became the standard structure for startup investment. Early VC firms, drawing from private equity traditions, recognized that companies could raise subsequent rounds at lower valuations — intentionally or not — and sought contractual protection for their invested capital.
Full ratchet was the original dominant form, borrowed from corporate finance instruments used in public markets. It was heavily criticized by founders for its harsh impact and began falling out of favor in the late 1990s as the balance of negotiating power shifted toward promising startups during the dot-com boom. Weighted average became the standard during this period because it was seen as more equitable to all parties.
The 2001 dot-com bust provided a real-world stress test. Many companies that had raised at astronomical valuations were forced into down rounds, and investors with full ratchet provisions exercised them aggressively, often wiping out significant founder ownership. This experience accelerated the industry-wide shift to broad-based weighted average, which is now the default in National Venture Capital Association (NVCA) model documents and Y Combinator term sheets.
Frequently asked questions
What is anti-dilution protection?
Anti-dilution protection is a clause in a preferred stock agreement that adjusts an investor's conversion price if the company later raises money at a lower valuation. It protects investors from losing purchasing power in a down round. Without it, an investor who paid $10/share in a Series A would see their position severely diluted if a later round prices shares at $5.
What is the difference between full ratchet and weighted average anti-dilution?
Full ratchet reprices the investor's entire position to the new lower price regardless of how much was raised. Weighted average is more balanced: it adjusts the conversion price based on the size of the down round relative to total outstanding shares. A small down round causes a smaller adjustment under weighted average.
Which type of anti-dilution is better for founders?
Broad-based weighted average anti-dilution is significantly more founder-friendly than full ratchet. Founders should push back hard against full ratchet provisions in term sheets — they are rare in normal market conditions and represent substantial downside risk if the company ever needs to raise at a lower valuation.
What is a down round?
A down round is a fundraising round where the company raises capital at a lower price per share than a previous round. Down rounds can happen when a company misses growth targets, market conditions worsen, or a previous round was priced too aggressively. Anti-dilution provisions exist specifically to protect investors who invested at the higher valuation in previous rounds.
Do common stockholders have anti-dilution protection?
No. Anti-dilution protection is a feature of preferred stock. Common stockholders — including founders and employees — have no anti-dilution protection. In a down round, founders bear the brunt of dilution while preferred investors have their positions partially protected.
What is a pay-to-play provision?
A pay-to-play provision requires existing investors to participate in a down round to maintain their anti-dilution protection. If they decline, their preferred shares convert to common stock, losing their anti-dilution and other preferred rights. Pay-to-play provisions encourage existing investors to support the company through difficult fundraising environments.
Can anti-dilution provisions be waived?
Yes. Investors can waive anti-dilution protection, and they often do in friendly down rounds where they want to support the company. Waivers require written consent and are typically negotiated alongside the down round terms. Some investors agree to waive in exchange for other consideration — additional shares, warrants, or more favorable new round terms.
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