The broad-based weighted average anti-dilution formula lowers a preferred investor’s conversion price after a down round using the equation CP2 = CP1 × (A + B) / (A + C), where the fraction is always less than one because the new round priced shares below the old conversion price. The lower conversion price means each preferred share converts into more common shares on exit. The “broad-based” label refers to how variable A is defined: it counts the company’s fully diluted share base, which keeps the adjustment moderate compared with harsher alternatives.1Carnegie Mellon University. Weighted Average Anti-Dilution Protection
What Each Variable Means
Four inputs drive the calculation:
- CP1 is the current conversion price before the down round, usually the price per share paid in the previous financing.
- A is the number of fully diluted shares outstanding immediately before the new issuance.
- B is the number of shares the new investment would have bought at the old conversion price, calculated as total new money divided by CP1.
- C is the actual number of new shares being issued in the down round, calculated as total new money divided by the new price per share.
Because the new price is lower than CP1, C is always larger than B, so (A + B) / (A + C) is always less than one. Multiplying CP1 by that fraction produces a lower conversion price, and the lower conversion price is what entitles the investor to more common shares on conversion.1Carnegie Mellon University. Weighted Average Anti-Dilution Protection
The formula self-calibrates. A small down round barely moves the price because C stays small next to A. A large round at a deep discount moves it noticeably because C swamps A. The adjustment tracks the real economic impact of the dilution rather than reacting to the discount alone.
What Counts in the Broad-Based Share Count
Variable A is where “broad-based” earns its name. The count is calculated on a fully diluted basis and includes all outstanding common stock, all preferred stock on an as-converted basis, and all outstanding options and warrants on an as-exercised basis.1Carnegie Mellon University. Weighted Average Anti-Dilution Protection Outstanding convertible notes and other convertible instruments also factor in because they represent potential equity claims. Shares that will be issued in the current down round itself are excluded from A, since including them would double-count the dilution the formula is trying to measure.
The sharpest negotiation point is the employee option pool. Including the unallocated portion of the pool, not just granted options, inflates A. A larger A pushes the fraction closer to one and softens the adjustment, which is why founders generally argue for including the full authorized pool. Many term sheets define the broad-based count to include the entire pool regardless of whether options have been granted.
Narrow-Based Weighted Average
A narrow-based weighted average uses the same formula but strips things out of A. It typically excludes the option pool and sometimes certain classes of preferred or warrants. A smaller A pushes the fraction further below one, producing a larger adjustment and a lower conversion price. Narrow-based favors the investor at the common holders’ expense and shows up far less often in modern venture financings because founders and their counsel push back on it during term sheet negotiation.
A Worked Example
A company closed its Series A at $1.00 per share. An early investor holds 400,000 Series A preferred shares. The company has 1,000,000 fully diluted shares outstanding. A new investor now puts in $500,000 at $0.50 per share.
- CP1 = $1.00
- A = 1,000,000
- B = $500,000 ÷ $1.00 = 500,000
- C = $500,000 ÷ $0.50 = 1,000,000
CP2 = $1.00 × (1,000,000 + 500,000) / (1,000,000 + 1,000,000) = $1.00 × 1,500,000 / 2,000,000 = $0.75.
The conversion price drops from $1.00 to $0.75. The investor’s 400,000 preferred shares now convert into 533,333 common shares (400,000 × $1.00 / $0.75) rather than the original 400,000. That is an extra 133,333 common shares at no additional cost.1Carnegie Mellon University. Weighted Average Anti-Dilution Protection
Notice how moderate the adjustment is. The new round priced shares at half the old value, but the conversion price only fell 25%. That tempering effect is the defining feature of the weighted average method.
How This Compares to Full Ratchet
Full ratchet anti-dilution ignores the size of the down round entirely and simply resets the conversion price to the new, lower price. In the example above, full ratchet would drop CP2 straight to $0.50. The 400,000 preferred shares would convert into 800,000 common rather than 533,333. Full ratchet treats a $500,000 bridge round at a discount the same way it treats a $50 million round at the same price.1Carnegie Mellon University. Weighted Average Anti-Dilution Protection
The downstream impact on founders is large. In a multi-round scenario modeled by Carnegie Mellon, the weighted average method left the entrepreneur with roughly 25 to 30 percent of the company, while the full ratchet method left them with about 10 percent.1Carnegie Mellon University. Weighted Average Anti-Dilution Protection
Issuances That Do Not Trigger the Formula
Not every new share issuance activates the adjustment. The certificate of incorporation lists specific “excluded issuances” that are carved out because they serve operational purposes rather than representing a repricing of the company’s equity. Standard carve-outs include common stock or options issued to employees, directors, or consultants under a board-approved compensation plan; stock issued on conversion of existing preferred, warrants, options, or convertible notes; shares issued in stock splits or stock dividends that affect holders proportionally; and shares issued for equipment leases, bank debt, acquisitions, joint ventures, or licensing arrangements that the board approves.
These exceptions are negotiated when the original investment is papered. How broadly or narrowly they are drafted matters, because any issuance that falls outside the carve-outs will trigger a recalculation even when the shares are issued for a legitimate business purpose.
Pay-to-Play Can Switch the Protection Off
Some charters condition anti-dilution protection on the investor actually participating in the down round. If the investor declines to buy their pro rata share, their preferred stock converts into common stock, or into a junior class of preferred that keeps some economic rights but loses the anti-dilution adjustment. The conversion usually runs one-to-one.
Pay-to-play counterbalances anti-dilution. Without it, a passive investor can sit out a difficult round, put in no new money, and still ride the price adjustment that active investors funded. The provision forces investors to either write a new check or accept the dilution alongside the founders. An investor who loses preferred status through a pay-to-play conversion also gives up the liquidation preference, board designation rights, and protective voting rights that attached to the preferred class.
What the Adjustment Does Not Change
The new conversion price changes the conversion economics only. The investor still holds the same number of preferred shares with the same dollar-for-dollar liquidation preference. The extra shares only materialize if the investor actually converts to common, which typically happens on an exit large enough that the bigger common position is worth more than the fixed preference amount. On the capitalization table, the conversion ratio for each affected series updates to reflect the new price; in the worked example, the ratio shifts from one-to-one to roughly 1-to-1.33.