What it means
When a company raises money at a lower valuation than before, earlier investors watch their percentage ownership shrink and the price they paid look expensive in hindsight. An anti-dilution provision partially compensates them by retroactively adjusting the price at which their preferred shares convert into ordinary shares.
Mechanically, the investor's original conversion price is reset downwards, which means each preferred share converts into more than one ordinary share. Nobody writes a cheque; the adjustment happens entirely in the share register, and the cost is borne by the founders and other holders of ordinary shares whose stake is squeezed further.
This matters in a business context because it shapes who absorbs the pain of a disappointing valuation. Founders negotiating a term sheet should treat the anti-dilution formula as a genuinely material commercial term, not boilerplate, because the difference between two versions of the clause can be several percentage points of the company.
There are two broad families. Full ratchet resets the earlier investor's conversion price all the way down to the new, lower price regardless of how few shares are sold at that price, which is severe and now uncommon outside distressed situations.
Weighted average, the market standard, resets the price only partly, scaled by how much new cheap stock was actually issued relative to the existing share count. Weighted average itself splits into broad-based and narrow-based versions, and the difference is which shares count in the denominator.
Broad-based includes options and other convertible instruments, producing a gentler adjustment, while narrow-based counts only outstanding preferred shares and hits founders harder. A common nuance is the "pay to play" condition, which makes anti-dilution protection conditional on the investor participating in the new round.
Standard carve-outs also exist so that routine issuances, such as shares under an employee option pool or shares issued to a lender, do not accidentally trigger the clause.
In practice
Real-world examples.
Example
A biotech startup raises a Series B at $12 per share, then eighteen months later raises a Series C at $7 after a trial setback. The Series B holders' broad-based weighted average clause lowers their conversion price to about $11.20, cushioning but not eliminating the loss of ownership.
Example
A consumer app company negotiates its seed round and pushes back on a full ratchet clause, arguing that it would leave the founding team with almost nothing after any down round. The investor accepts broad-based weighted average in exchange for a board observer seat.
Example
A hardware manufacturer's cap table shows that a narrow-based clause would cost the two founders roughly four percentage points of ownership in a modelled down round, while the broad-based alternative costs about one and a half. The founders raise this with their lawyer before signing.
Think of it
“Anti-dilution protects investors from losing ownership percentage in later fundraising rounds.
Formula
Calculation
Broad-based weighted average new conversion price: NCP = OCP x (A + B) / (A + C), where OCP is the old conversion price, A is the fully diluted shares outstanding before the new round, B is the number of shares the new money would have bought at the old price, and C is the number of shares actually issued in the new round.
Assume an investor bought preferred shares at $10.00 each, the company has 8,000,000 fully diluted shares outstanding, and it now raises $2,000,000 at $5.00 per share. That gives A = 8,000,000, B = 2,000,000 / 10 = 200,000, and C = 2,000,000 / 5 = 400,000.
NCP = 10.00 x (8,000,000 + 200,000) / (8,000,000 + 400,000) = 10.00 x 8,200,000 / 8,400,000 = $9.76.
An investor holding 1,000,000 preferred shares now converts at $9.76 rather than $10.00. The conversion ratio becomes 10.00 / 9.76 = 1.0244, so those preferred shares turn into about 1,024,390 ordinary shares instead of 1,000,000, an extra 24,390 shares. Under a full ratchet the conversion price would have dropped all the way to $5.00, doubling the position to 2,000,000 ordinary shares, which shows how much harsher that version is.Case study
Seen in the real world.
Pellworth Robotics is a fictional company invented for this illustrative walkthrough. It raised $6,000,000 at $10.00 per share from a single institutional investor, with a broad-based weighted average anti-dilution clause and a standard carve-out for the employee option pool.
Two years later a major customer pulled a contract and the company needed money quickly, accepting $2,000,000 at $5.00 per share from a new backer. The anti-dilution clause reset the original investor's conversion price to $9.76, giving them roughly 2.4% more ordinary shares on conversion than they would otherwise have received.
The founders had budgeted for dilution from the new shares themselves but had not modelled the anti-dilution adjustment on top, and in this illustrative scenario the extra squeeze came as an unpleasant surprise during the closing process. The lesson the fictional board drew was to keep a live cap table model showing the effect of a down round at several price points, so the clause is understood before it is ever needed.
Watch out
Common mistakes.
- Assuming anti-dilution protects against any reduction in ownership percentage, when it only responds to shares issued below the earlier price.
- Treating full ratchet and weighted average as broadly similar, when full ratchet can transfer several times more value away from founders.
- Ignoring the carve-out list, so that a routine option pool top-up or a warrant to a lender unexpectedly triggers an adjustment.
Questions
People also ask.
Does the investor pay anything for the extra shares?
No, the adjustment changes the conversion price on shares already bought, so the value comes out of other shareholders' stakes.
What is a pay-to-play provision?
It makes anti-dilution protection conditional on the investor putting money into the new round, which discourages passive investors from claiming protection while others fund the company.
Do ordinary shareholders ever get anti-dilution protection?
Rarely in this form, since the mechanism works through preferred share conversion rights, though ordinary holders may negotiate pre-emption rights instead.
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