Equity dilution: what actually shrinks, and what does not.

The mechanism is one line of arithmetic

Ownership is a fraction: the shares you hold, over the total outstanding. Dilution is what happens when the company issues new shares — the numerator stays where it was and the denominator gets bigger. Nobody takes anything away from you. Everything else written about dilution is a variation on that one fraction.

This guide assumes the US default: a Delaware C-corporation, common stock for founders and employees, preferred stock for investors. Delaware law puts the authorized share count and the classes in the certificate of incorporation, and changing either — more authorized shares, or a new series for a round — runs through the amendment procedure in DGCL §242, which needs board and stockholder action. The mechanics generalise elsewhere; the statutory references do not.

Financing percentages are quoted fully diluted — options, warrants and convertible instruments counted as if already converted — because that is what the round is priced against. That ledger is covered at /equity/cap-table; why the authorized count is not the denominator is at /equity/authorized-vs-outstanding-shares.

A priced round, worked end to end

Take a fully diluted cap table of 8,000,000 founder shares plus a 2,000,000-share option pool: 10,000,000 in total, so founders are at 80.0% and the pool at 20.0%. The company raises $4,000,000 at a $16,000,000 pre-money valuation. Pre-money plus new money is post-money, so it is priced at $20,000,000 once the round closes.

Why dilution is usually the price of something worth having

Dilution is what capital costs, and the only question is whether the capital buys more than the slice it consumed. Say the company later sells another 20.0% of itself at a $50,000,000 post-money. Founders go from 64.0% to 51.2%, because 64.0% × 0.8 = 51.2%. That 51.2% is worth $25,600,000, against $12,800,000 before. Percentage down another fifth; value doubled. That is the ordinary case, and why percentage alone tells you very little.

Dilution hurts when the second half of that sentence fails. In a down round the company sells shares at a lower price than last time, so the same cash buys more shares, the percentage falls further, and because the price itself is lower the value of the remaining stake falls with it. The same holds for any raise where the money does not add at least as much value as the ownership it cost. Either way, dilution is the receipt, not the problem.

The three things that dilute you

New rounds of stock

This is the worked example above. A round almost always creates a new series of preferred rather than more common, and DGCL §151(a) is what permits it: a corporation may issue classes of stock, or series within a class, with voting powers that are full, limited or none, and with the preferences and special rights stated in the certificate of incorporation. So a Series A does not only add shares — it adds a rights stack sitting above the common. See /equity/common-vs-preferred-stock.

Option pool creation or expansion

Reserved employee shares count in the fully diluted denominator, so creating or topping up a pool dilutes for the same reason a round does. The wrinkle is timing: when an investor requires the pool to be set inside the pre-money, the shares are added before the price is struck, so existing holders absorb the whole cost and the incoming investor absorbs none. The shuffle is worked through at /equity/option-pool. Options are separately granted at a strike equal to fair market value, established by a valuation intended to satisfy 26 U.S.C. §409A — which changes what an option is worth, not how much it dilutes.

SAFEs and convertible notes converting

These are not on the equity line until they convert, so a cap table showing only issued shares systematically overstates what everyone owns. A valuation cap makes the instrument convert at a lower effective price per share than the round price; a discount does the same by another route. Either way the holder gets more shares than the headline price implies, and the extra shares come out of everyone already there. How much depends entirely on the cap, the discount and the round price, so model your own terms — /tools/safe-note-calculator does that arithmetic.

What does not dilute you

Three events change share counts without diluting anyone. They get confused with dilution constantly.

Anti-dilution protection is not what the name suggests

Preferred stock issued in a financing frequently carries a price-based anti-dilution adjustment. It does not stop new shares being issued and it does not preserve anyone’s percentage. It changes the rate at which preferred converts into common if the company later sells stock below the price the earlier investor paid. Broad-based weighted average is the common formulation, adjusting the conversion rate by reference to how many shares were sold and at what price. Full ratchet is the aggressive version, resetting the rate as if the earlier investor had paid the new, lower price.

Two consequences are easy to miss. The adjustment protects the preferred holder, and the extra common shares they receive on conversion come at the expense of common stockholders and option holders — founders and employees. And it is not protection against ordinary dilution from an up round; it engages only when a later round prices below an earlier one. The formula is negotiated, so read the charter language rather than the label. /equity/common-vs-preferred-stock has the rest of the preferred rights stack.

Percentage is not control, and not proceeds

A smaller share of a larger company can come with less control, but the two move independently. Voting power is a property of the share class: DGCL §151(a) lets a corporation create a class or series whose voting powers are full, limited, or none. Board composition is set separately, in the charter and the financing documents. In practice the protective provisions in a preferred financing — the actions needing preferred consent — often matter more than any ownership number. /equity/share-classes covers both.

Percentage is also a poor predictor of what a holder is paid. The SEC’s investor education material puts the ordering plainly: if a company goes bankrupt and its assets are liquidated, common stockholders are last in line — bondholders are paid first, then holders of preferred stock. Liquidation preferences follow the same shape in a sale, which is why two people holding the same percentage can be paid very different amounts.