What is Dilution?
Short answer: Dilution is a reduction in a holder's percentage ownership, voting power, earnings participation or share of exit proceeds following a change in capitalization. It usually occurs when a company issues shares or when options, warrants, notes or SAFEs convert and the holder does not receive enough additional shares to maintain its percentage. Dilution of percentage ownership does not by itself prove that the holder's stake lost value.
Several forms should be distinguished. Financing dilution comes from shares issued for new capital. Pool dilution comes from creating or enlarging employee equity reserves. Conversion dilution comes from outstanding share-linked instruments. Economic dilution can also arise when a new class has a senior liquidation preference even if voting percentages appear stable. Anti-dilution provisions are contractual price adjustments for specified down rounds, not a general promise against all dilution. Pre-emption or pro rata rights may let a holder invest more to maintain ownership, but they usually require timely exercise and additional cash.
How it works
Choose the denominator before calculating. Issued ownership uses shares legally outstanding. As-converted ownership treats specified convertible securities as shares. Fully diluted ownership may also include options, warrants and an unallocated pool. Build a bridge from the opening share count through each issuance, conversion, cancellation and pool change. For each step, divide the holder's shares by the new total. Model voting, preference and proceeds separately. To calculate how many shares a holder must buy to maintain a target percentage, solve for its target post-issue shares and deduct shares already held, taking account of the new shares it buys in the denominator.
Post-issue ownership = holder post-issue shares / total post-issue shares on the stated basis
Example
A founder holds 720,000 of 900,000 issued shares, or 80%. The company first adds a 100,000-share option pool, taking the fully diluted total to 1,000,000 and the founder to 72%. It then issues 250,000 shares to an investor. The total becomes 1,250,000 and the founder owns 57.6%. If the founder has a valid pro rata right and buys 50,000 of the new shares while the outside investor buys 200,000, the founder holds 770,000 of 1,250,000, or 61.6%. The founder was still diluted from 80%, but participation reduced the decline. A preference waterfall could produce a different economic share at exit.
Why it matters
Dilution analysis helps founders decide the size and timing of a raise, employees understand incentive value, and investors assess follow-on needs. Boards should compare dilution with the value and runway created by new capital. Issuing 20% of the company can benefit existing holders if the funding increases the company's total value sufficiently, but that outcome is uncertain. A financing model should show base, downside and later-round cases, including pool requirements and conversion overhang. It should also identify which holders can participate and how much cash they would need.
The legal share register, constitutional documents and financing agreements determine actual shares and rights. Fully diluted conventions differ, and accounting diluted earnings per share is a separate calculation governed by reporting standards. Anti-dilution formulas vary and may exclude employee grants, acquisitions or other permitted issuances. Option exercise, tax and securities consequences depend on holder and jurisdiction. Percentage calculations can mislead when classes have different votes, preferences or conversion rights. Reconcile the model to authorised capital, board and shareholder approvals, signed instruments and closing records before using it for a decision.