What Is Anti-Dilution Protection?
Anti-dilution is a contractual right that gives preferred shareholders extra shares (or a lower conversion price, which is the same thing) if the company later raises at a lower valuation than they paid. It protects the price-per-share they bought at — not the percentage of ownership they hold.
There are two flavours: full ratchet and weighted average. They sound similar and produce wildly different outcomes. Weighted average is the market standard and what every founder should push for. Full ratchet is brutal and only appears in distressed rounds, structured growth deals, or when founders signed a term sheet without reading it.
Anti-dilution only triggers on a "dilutive issuance" — a new round priced below the prior round. Issuing options from the employee pool, exercising warrants, or converting existing convertibles does not trigger it (these are usually carved out explicitly).
How Anti-Dilution Works
Full ratchet resets the investor's conversion price to the new round's price. If they paid €10/share and the next round prices at €4/share, their conversion price becomes €4 — meaning their original €5M investment now converts as if they had bought at €4, giving them 2.5× more shares. This dilutes the founders heavily.
Weighted average uses a formula that blends the old and new prices, weighted by how much new money was raised and how many shares were already outstanding. Broad-based weighted average (the founder-friendly version) includes the entire cap table on a fully diluted basis in the denominator; narrow-based excludes the option pool, producing a slightly more aggressive adjustment.
The formula for broad-based weighted average: New Conversion Price = Old Price × (A + B) / (A + C), where A = shares outstanding before the new round (fully diluted), B = shares that would be issued if the new money was raised at the old price, C = shares actually issued in the new round.
Key Terms and Definitions
Conversion price — the price at which a preferred share converts to common. Lower conversion price = more common shares per preferred share = more dilution for everyone else.
Broad-based vs. narrow-based — refers to which shares are counted in the formula denominator. Broad-based includes the entire fully diluted cap table (founder-friendly). Narrow-based excludes options and warrants (investor-friendly, produces a larger adjustment).
Dilutive issuance — a new share issuance at a price below the preferred class's current conversion price. This is the trigger event.
Carve-outs — categories of share issuance explicitly excluded from triggering anti-dilution. Standard carve-outs include: ESOP grants, warrants issued to lenders, shares for acquisitions, and conversions of existing convertibles.
Pay-to-play — a clause that forces existing investors to participate pro-rata in the down round or lose their anti-dilution protection (and sometimes their preferred status). See [recapitalization](/captable/recapitalization) for related mechanics.
Why Anti-Dilution Matters for Founders
The big mistake is treating anti-dilution as a binary "do we have it or not" question. It is always there — the negotiation is over which flavour and how broad the carve-outs are. A founder who accepts narrow-based weighted average instead of broad-based has signed up for material extra dilution in any future down round, and most founders cannot articulate the difference.
The second mistake is signing full ratchet under pressure. Full ratchet exists; investors sometimes propose it; it should be a non-starter except in genuine rescue financings. The realistic concession ladder runs: broad-based weighted average (default), narrow-based weighted average (acceptable under pressure), full ratchet (only as the price of saving the company).
Carve-outs matter as much as the formula. Push for explicit exclusion of: option pool top-ups (your team needs to be paid in equity even in tough times), conversion of existing notes and SAFEs (those were already priced in), strategic warrants, and acquisition-related issuances. Without these carve-outs, every routine cap table action drags you toward a partial adjustment.
Common Scenarios
Bridge before down round: company raises a small convertible note to extend runway. If the note converts at a lower implied price than the Series A conversion price, the anti-dilution mechanism may trigger. This is why carve-outs for convertible note conversion matter.
Recap with new lead investor: existing investors take a haircut as part of the cleanup. Pay-to-play forces them to participate or lose anti-dilution protection. Founders sometimes regain meaningful ownership through this process. See [recapitalization](/captable/recapitalization).
Flat round dressed as a down round by the option pool shuffle: a new round at the same headline price-per-share, but with a large pre-money option pool top-up that effectively lowers the price. The anti-dilution math depends on how the pool is treated in the formula. See [option pool shuffle](/captable/option-pool-shuffle).
How CAPLINK Helps You Manage Anti-Dilution
CAPLINK's cap table module stores the anti-dilution clause type, base, and carve-outs for every preferred class. When you model a new round, the scenario engine automatically applies the correct anti-dilution adjustment to every prior class and shows you the resulting fully diluted cap table — so a "what if Series B prices at €4 instead of €8?" question takes 30 seconds, not 30 minutes of careful Excel work that is wrong half the time.
This matters most when you are mid-negotiation on a difficult round and need to understand how much existing-investor dilution buffer you have to negotiate against. It also matters during due diligence: prospective Series B investors will model your downside themselves, and a cap table where the anti-dilution effect is pre-modelled and documented in the [data room](/dataroom) avoids hours of back-and-forth.
Read the [liquidation preference guide](/captable/liquidation-preference) for how preferences and anti-dilution compound at exit, and [equity dilution](/captable/equity-dilution) for the broader picture of founder ownership across rounds.