Glossary · Shareholder rights & company governance

Dilution

Also called: equity dilution · ownership dilution

Dilution is the reduction in an existing shareholder's percentage ownership when a company issues new shares, including through financing rounds, conversion of simple agreements for future equity (SAFEs) and notes, option grants, warrants and anti-dilution adjustments.

Publisher: Altss LLCContent modified 2026-10-01

ALTSS-VC-028

A shareholder's slice of the company gets smaller every time new shares are created for someone else. Whether the slice is also worth less depends on the price of the new shares: selling shares at a fair price shrinks the percentage but not the value of the stake; selling them cheaply shrinks both.

Formulas

Ownership after an issue

New ownership = old ownership × old shares / (old shares + new shares)

o₀, o₁: ownership before and after the issue
S₀: total shares before the issue, on the same basis as o₀ (usually fully diluted)
N: new shares issued to others

Measure o and S on the same basis. Ownership on an issued-and-outstanding basis is higher than on a fully diluted basis, and the two dilute differently when options are granted from an existing pool.

Cumulative dilution across rounds

Ownership after n rounds = starting ownership × product of (1 − fraction of post-round shares sold or added in each round)

f_i: new shares in round i (including any pool increase) as a fraction of post-round fully diluted shares

Assumes the holder does not participate in any round.

Percentage dilution and value dilution

Every issue of new shares to someone else reduces existing holders' percentage. It reduces the value of their stake only if the new shares are issued for less than they are worth. Issuing shares at the round price in an up round is value-neutral at the moment of issue and usually funds growth; value dilution comes from issues below value: down rounds, discounted conversions of SAFEs and convertible notes, anti-dilution shares, and options granted as compensation.

Sources of dilution

New primary shares in a priced round; conversion of SAFEs and notes; creation or enlargement of the option pool; exercise of warrants; anti-dilution adjustments; shares issued in acquisitions. Who bears each source depends on the terms: a pool increase inside the pre-money dilutes existing holders only, post-money SAFEs place the dilution from later SAFEs on existing holders, and anti-dilution adjustments shift dilution from protected preferred to everyone else.

How investors manage it

Venture investors model ownership from entry to exit because fund returns depend on the percentage held when a company is sold. They use pro rata rights and follow-on reserves to limit dilution in their best companies, and accept it in the rest. Founders track cumulative dilution because control and incentives depend on it.

Dilution in public company accounting

In financial reporting, "dilution" also appears in diluted earnings per share, an accounting measure of profit per share. That measure answers a different question: how much profit is attributable to each share, not what fraction of the company a holder owns.

Worked examples

Illustrative single round

A founder owns 4,000,000 of 10,000,000 fully diluted shares (40%). The company issues 2,500,000 new shares. The founder now owns 32%. If the shares were sold at $4.00, the pre-money was $40m and the founder's stake was worth $16m; post-money is $50m and 32% of it is still $16m. The percentage fell; the value did not.

Three rounds

A founding team owns 60% after its seed round. A Series A sells 20% of the post-round company, and a Series B sells 15%, each including any pool top-up. The team keeps 0.80 × 0.85 = 68% of its stake through both rounds and ends at 60% × 0.80 × 0.85 = 40.8%. Had there been a further 20% round before the A, the same arithmetic would leave it at 32.6%.

Examples are illustrative; figures are not market data.

Not the same as

Anti-Dilution Protection: Anti-dilution protection is a contractual remedy for one kind of dilution, issuance below a protected price.
Fully Diluted Shares: Fully diluted shares is the share count used as the denominator; dilution is the change in a holder's share of it.
Write-Down: A write-down reduces the carrying value of a holding; dilution reduces ownership percentage and may or may not reduce value.

Common mistakes

Treating every dilutive round as a loss of value.
Measuring ownership on issued shares while measuring dilution on fully diluted shares.
Leaving unconverted SAFEs and notes out of the dilution analysis.
Adding round percentages together instead of multiplying the retention factors.

Questions

Does dilution reduce the value of my shares?

Not necessarily. Shares issued at a fair price reduce a holder's percentage but not the value of its stake; shares issued below value reduce both.

How much dilution is normal per round?

It depends on the company and the market; there is no standard. Model each round from its actual terms rather than a rule of thumb.

Sources

Glossary (capital formation terms). U.S. Securities and Exchange Commission, Page last updated 2024-02-02. Status: current (checked 2026-10-01). entry: Dilution (page updated 2024-02-02) — supports: Dilution occurs when a company issues new shares, leaving existing stockholders with a smaller percentage ownership interest

6 terms

3 terms

Concept record

Concept ID: ALTSS-VC-028
Classification: Shareholder rights & company governance
Topics: Venture capital & startups
Version: 2.0.0
Last reviewed: 2026-10-01
Structured data: JSON