Key Takeaways
- Anti-dilution protection lowers the conversion price of preferred stock when a company later issues shares at a lower price — a down round — so preferred holders convert into more common shares
- It does not issue new preferred shares; it changes how many common shares each preferred share converts into, and the extra shares come out of everyone else's ownership
- Broad-based weighted average is the market standard and the formula in the NVCA model charter; it moves the price part of the way toward the new price, scaled by how much stock was sold
- Full ratchet resets the conversion price all the way to the new lower price regardless of how few shares were sold, and is rare outside distressed financings
- Narrow-based weighted average uses a smaller share count in the formula and produces a bigger adjustment than broad-based
- Down rounds were 12.1% of deals in Cooley's Q2 2026 report, so the clause is not theoretical
- Founders should accept broad-based weighted average, negotiate carve-outs for option grants and conversions, and refuse full ratchet outside a rescue round
Anti-dilution protection is a clause in a company's charter that lowers the conversion price of an investor's preferred stock if the company later sells shares at a lower price. Broad-based weighted average, the market standard, adjusts the price modestly based on how much stock the down round sold. Full ratchet resets it entirely to the new price and shifts far more ownership away from founders.
This guide is general information, not legal advice. The exact formula, share-count definitions and carve-outs live in your certificate of incorporation, and your counsel should model them against your cap table.
What Is Anti-Dilution Protection?
Anti-dilution protection compensates preferred investors for a down round by letting them convert their preferred stock into more common shares than they originally bargained for. It is negotiated in the term sheet and written into the company's certificate of incorporation.
Every share of preferred stock is convertible into common stock. The number of common shares it converts into is the original purchase price divided by the conversion price. At closing, both numbers are the same, so one preferred share converts into one common share.
If the company later sells stock at a lower price, the anti-dilution clause lowers the conversion price. Lower conversion price means each preferred share converts into more common. As Cooley's broad-based weighted average glossary entry and AngelList's guide to anti-dilution protection both describe, the adjustment works through conversion, not through new preferred shares being issued.
This is a different problem from ordinary dilution. The SEC's investor education site defines dilution as the reduction in ownership percentage when new shares are issued. Every round dilutes everyone. Anti-dilution protection does not stop that. It only protects against the price of new shares being lower than what the investor paid.
There are two separate kinds of adjustment in most charters:
How Common Are Down Rounds in 2026?
Down rounds made up 12.1% of the venture financings in Cooley's Q2 2026 data, up from 10.9% in Q1. That is roughly one deal in eight, which is why the anti-dilution formula deserves attention at the seed and Series A stage, not only when a company is in trouble.
Cooley's Q2 2026 Venture Financing Report also shows pay-to-play provisions in 8.4% of deals, up from 7% in Q1. Pay-to-play is closely tied to anti-dilution: it strips the protection from investors who do not participate in a later round.
A down round does not need to be a crisis to trigger the clause. A bridge priced below the last round, a strategic investor buying at a discount, or a valuation reset after a hot round can all be a price below the current conversion price.
How Does Broad-Based Weighted Average Anti-Dilution Work?
Broad-based weighted average lowers the conversion price part of the way toward the new price, in proportion to how much new stock was sold relative to the company's whole capitalization. A small down round barely moves the price; a large one moves it more, but never all the way.
The formula used in the NVCA model legal documents, the charter templates most US venture rounds start from, is:
CP2 = CP1 × (A + B) ÷ (A + C)
The logic is simple. If the new investors had paid the old price, they would have received B shares. They actually received C, which is more. The formula moves the price by the ratio of what the company would have issued to what it did issue, weighted against everything already outstanding.
"Broad-based" refers to A. In a broad-based formula, A includes all common stock, all preferred on an as-converted basis, and outstanding options and warrants; many charters also include the unissued option pool. A larger A dilutes the effect of the new shares and produces a smaller adjustment.
How Does Full Ratchet Anti-Dilution Work?
Full ratchet resets the investor's conversion price to the exact price of the new, lower-priced shares, no matter how many shares were sold. Selling a single share at a lower price triggers the full adjustment.
Cooley's glossary entry on full ratchet describes it as the most investor-favorable form of price-based protection. The investor ends up in roughly the position they would have been in had they invested at the down-round price from the start.
The problem is that the formula ignores scale. A $500,000 bridge at a lower price produces the same price reset as a $50 million recapitalization at that price. All of the extra common shares come from the holders who do not have the protection: founders, employees and any investors without it.
Full ratchet also makes the next round harder. New investors pricing a down round have to model a cap table in which earlier investors convert into far more shares, which raises the effective dilution of their own price and can push a marginal deal into a recapitalization.
What Is the Difference Between Broad-Based and Narrow-Based?
Broad-based and narrow-based weighted average use the same formula; they differ only in how many shares count as A. A narrow-based formula counts fewer shares, so the same down round produces a larger price adjustment.
As AngelList's guide explains, a narrow-based approach often counts only outstanding preferred shares. That leaves out common stock, options and warrants, and the calculation lands closer to full ratchet than to broad-based.
Read the definition of "outstanding shares" in the draft charter, not just the label in the term sheet. A term sheet that says "broad-based weighted average" while the charter excludes the option pool from A is narrower than it sounds.
Worked Example: How Much Does Each Formula Cost Founders?
In this illustrative example, the same down round adds 652,174 shares to the Series A investor under broad-based weighted average, 1,875,000 under narrow-based, and 5,000,000 under full ratchet. The numbers are a hypothetical cap table built to show the mechanics, not a real company.
The setup:
Without any anti-dilution adjustment, the company has 26,000,000 shares after the Series B and the founders own 38.5%.
Broad-based weighted average
Narrow-based weighted average
Full ratchet
The comparison in one place:
Run your own numbers before you sign. The GIGABOOST dilution calculator models round-by-round ownership, and the option pool shuffle explains another place where the share count quietly moves value.
Which Issuances Should Not Trigger Anti-Dilution?
Carve-outs, called exempted or excluded securities, list the share issuances that never trigger a price adjustment, even if they happen below the conversion price. Without them, routine events like an option grant at a low 409A price could technically trigger the clause.
The NVCA model charter includes a standard list. Confirm at least these are excluded:
Also negotiate a waiver mechanism. Most charters allow the holders of a defined majority of preferred to waive an adjustment for the whole class. That lets a down round close when the majority agrees, instead of every investor holding a veto. Changes to the preferred's rights generally require a charter amendment, which in Delaware runs through the class-vote rules in Subchapter VIII of the Delaware General Corporation Law.
Do SAFEs and Convertible Notes Have Anti-Dilution Protection?
A standard post-money SAFE has no price-based anti-dilution clause of its own; it converts into preferred stock in the next priced round and picks up whatever protection that round's preferred carries. The same is generally true of convertible notes.
The Y Combinator SAFE documents define how the SAFE converts — at the valuation cap or discount — but do not adjust the cap if the company later raises at a lower price. Once the SAFE converts into a series of preferred, the anti-dilution terms in the charter for that series apply.
SAFE holders still face dilution from later SAFEs and the option pool. That is a separate calculation, covered in how SAFE dilution works.
What Should Founders Accept in a Term Sheet?
Accept broad-based weighted average with a full set of carve-outs; push back on narrow-based; refuse full ratchet unless the round is a rescue financing with no alternative. That position matches the NVCA model documents and what most institutional leads expect.
A practical checklist for the anti-dilution section of a term sheet:
The best protection against anti-dilution costs is not negotiating a down round at all. A defensible valuation at each round keeps the clause dormant. The GIGABOOST AI company valuation tool benchmarks your valuation before you set a price, so the next round has room to be an up round.
Price your next round so the anti-dilution clause never fires
GIGABOOST benchmarks your valuation, reviews your deck and matches you against 340,000+ verified investors scored on 25 fit factors. $1 for the 7-day trial, 15 investors revealed.Frequently Asked Questions
What is anti-dilution protection in venture capital?
Anti-dilution protection is a charter provision that lowers the conversion price of an investor's preferred stock if the company later sells shares at a lower price. The investor's preferred then converts into more common shares, which offsets part or all of the loss in value from the down round. The extra shares reduce the ownership of founders, employees and any holders without the protection.
What is the difference between full ratchet and weighted average anti-dilution?
Full ratchet resets the conversion price to the new, lower price no matter how many shares were sold. Weighted average moves the conversion price only part of the way, in proportion to how much new stock the down round issued relative to shares already outstanding. Weighted average, especially the broad-based version, costs founders far less ownership.
Which anti-dilution formula is standard for startups?
Broad-based weighted average is the market standard in US venture financings and is the formula used in the NVCA model certificate of incorporation. Narrow-based weighted average and full ratchet appear less often and usually signal either investor leverage or a distressed financing.
Does anti-dilution protection issue new shares to investors?
No. The adjustment changes the conversion price, so each existing preferred share converts into more common stock when it converts. No new preferred shares are issued at the time of the down round. The economic effect is still a transfer of ownership away from holders without the protection.
Can anti-dilution protection be waived?
Yes. Most charters allow holders of a defined majority of the preferred stock to waive an anti-dilution adjustment for the entire class. Lead investors in a down round often require existing investors to waive as a condition of closing, sometimes through a pay-to-play structure.
Do SAFEs have anti-dilution protection?
A standard Y Combinator post-money SAFE does not adjust its valuation cap if the company later raises at a lower price. When the SAFE converts into preferred stock in a priced round, it takes on whatever anti-dilution protection that round's preferred carries under the charter.