October 1, 2026 · 8 min read
What Is Share Dilution? Definition, How It Works and Examples
Why your slice of a company shrinks each time it raises money, when that costs you value and when it does not.
- Dilution
- Cap tables
- Funding rounds
Share dilution explained in one line: it is the fall in your percentage of a company when the company issues new shares. The new shares come from a funding round, from an employee option pool, or from convertible notes and SAFEs (early investments that turn into stock later). You still hold the same number of shares. The total they are divided by grows.
If you own shares in a private company, as an employee, an early investor or through a fund, a smaller percentage does not mean you lost money. If the new shares sell above the price you paid, your stake can be worth more after the round than before it. Dilution costs you value in a down round, when new shares sell for less than in the last round. Then anti-dilution protection decides who absorbs the loss. Some classes of preferred stock, the shares investors buy, carry it. Others do not.
Stock Dilution Explained: Percentage vs Value
The arithmetic takes one line. Your new percentage is your shares divided by the old total plus the new shares. Say a round issues new shares equal to 25% of the company after it closes. Every existing holder keeps 75% of the percentage they had, so 10% becomes 7.5%.
Whether that is good or bad depends on the price. Hold 10% of a company worth $10M, and your stake is worth $1M. Now the company sells new shares at a $15M pre-money valuation, its value just before the new money arrives. Your 10% shrinks. But your shares are now priced at a valuation 50% higher, so your stake is valued at $1.5M. The percentage fell, and the value rose. The same round at a $6M pre-money valuation would leave you a smaller percentage of a company priced lower. That is dilution and a markdown, a cut in the value of your stake, at once.
Stock dilution in a listed company works the same way. It comes from follow-on offerings (new shares sold after the company has listed), employee share plans and convertible bonds. A listed company reports its share count every quarter. In a private company, new shares are priced in a negotiation between the company and its investors. You see the count only when the company tells you.
Share Dilution in a Private Company, Round by Round
Private company share dilution comes from three sources, and the example below has all three. Two founders hold 8,000,000 shares, with a 1,000,000-share option pool for future staff. An angel investor puts in $1M on a post-money SAFE with a $10M cap, the highest valuation at which it converts. A Series A raises $7.5M at a $22.5M pre-money valuation. Its condition is that the pool grows to 15% of the company after the round. A Series B then raises $15M at a $60M pre-money valuation.
Illustrative numbers for an invented company. Percentages are fully diluted and rounded. Preferred is counted as converted one for one. The SAFE converts at the Series A
Across two rounds, the founders’ percentage falls from 88.9% to 42.7%. Over the same period, the value of their 8,000,000 shares goes from unpriced to $32M. That is share dilution working as intended. See cap table for how each line sits on the register.
SAFEs and Convertible Notes
A SAFE or a convertible note becomes a share only at a priced round. So it is easy to leave off the count, yet it dilutes all the same. The post-money SAFE has been the standard of Y Combinator, a startup accelerator, since 2018. On it, the ownership sold equals the investment divided by the post-money valuation cap: $1M on a $10M cap is 10%. Here it converts into 1,000,000 shares at $1.00, half the Series A price. That takes the founders from 88.9% to 80.0% before the Series A money arrives. A convertible note, a loan that turns into shares, converts its principal plus accrued interest the same way.
The Option Pool Shuffle
The 1,250,000 new pool shares were created before the Series A, inside its $22.5M pre-money valuation. At $2.00 a share, they are worth $2.5M. So for the founders and the SAFE holder, the effective pre-money valuation was $20.0M. The option pool shuffle puts the dilution from future hires on the holders already there, and the new investor avoids it. The size of the top-up is negotiable, if anyone at the table notices it.
What Is Anti-Dilution Protection for Shares? Full Ratchet vs Weighted Average
Anti-dilution protection is a clause in the certificate of incorporation, the company’s charter. It lowers a preferred class’s conversion price when the company later sells shares cheaper than that class paid. The conversion price sets how many common shares each preferred share turns into. A lower price means more common shares, so the protected class keeps more of its percentage. Those extra shares come out of everyone else’s percentage. The clause applies in a down round only. Ordinary dilution at a higher price does not trigger it.
The Broad-Based Weighted-Average Formula
Delaware venture charters filed with the SEC, the US securities regulator, write it as CP2 = CP1 × (A + B) ÷ (A + C), where:
- CP2
- The conversion price immediately after the new issue.
- CP1
- The conversion price immediately before it.
- A
- Common shares outstanding before the issue, counting shares issuable on outstanding options and convertibles. Counting these is what makes the formula “broad-based.”
- B
- The shares the new money would have bought at CP1: the amount raised divided by CP1.
- C
- The new shares actually issued.
A narrow-based version counts fewer shares in A, which gives a larger adjustment. A full ratchet ignores the size of the new issue. It simply resets the conversion price to the new, lower price. Now continue the example with a down round, a round priced below the one before it. A Series C raises $5M at $2.50 a share, below the Series B price of $4.00, and issues 2,000,000 shares. Series B has protection. Series A paid $2.00, so the new price does not affect it.
Illustrative, continuing the example. Weighted average: $4.00 × (18,750,000 + 1,250,000) ÷ (18,750,000 + 2,000,000) = $3.855, rounded
Here, a broad-based weighted average costs the founders three-tenths of a point. A full ratchet costs them almost four points. In a down round, the form of the clause decides how much of the markdown lands on the holders who have no protection.
Pro Rata Rights, and What Dilution Means Through an SPV
The other way to resist dilution is to buy more. A pro rata right lets an investor buy into each new round in proportion to its holding. In the example, the Series A investors hold 25% before the Series B. To stay at 25%, they would buy 937,500 of the 3,750,000 new shares, for $3.75M. Under Delaware law, no stockholder has a preemptive right, a right to buy new shares first, unless the certificate of incorporation grants it. So pro rata is usually a contract in the financing agreements, often limited to larger investors.
Share Dilution Through an SPV
A single-deal vehicle, or SPV, holds a fixed number of shares. So its percentage dilutes exactly like that of any other holder of the same class. Two things decide how much that matters. The first is the class. Common stock bought from an employee on the secondary market, where existing holders sell to new buyers, carries no anti-dilution protection. A series of preferred may carry it. The second is the rights. A pro rata right usually belongs to the original investor and does not automatically come with shares bought second-hand. A vehicle that has already invested also has no new money to use one, unless its documents provide for it. What an SPV is covers who holds the rights. The page on fees and costs lists dilution among the costs nobody charges.
The Rules Behind Dilution and Anti-Dilution, as of October 2026
As of October 2026 · Delaware Code Title 8; SEC EDGAR (filed charter); Y Combinator; NVCA
Common Mistakes About Share Dilution
- Measuring dilution in percent onlyA smaller share at a higher price can be worth more. Price decides whether dilution is a loss.
- Forgetting SAFEs and notesThey dilute at the next priced round, whether or not they appeared on the last cap table you saw.
- Taking the pre-money at face valueA pool top-up inside the pre-money valuation lowers the price existing holders were really paid.
- Assuming anti-dilution protects everyoneIt protects one class. The shares it adds dilute every holder without it, starting with common.
- Treating full ratchet and weighted average as similarIn the example, one moves the founders by 0.3 points and the other by 3.8.
- Assuming a pro rata right existsIt does not exist by default. It also does not automatically travel with shares bought on the secondary market.
Option holders feel dilution through the strike price, the price they pay to buy each share, as well as through the percentage. See 409A valuation for why that price sits below the price of preferred stock, and pre-IPO shares for the share classes themselves.
The Terms This Page Uses
- Fully diluted
- A share count that includes everything that could become a share: options, the unallocated pool, warrants and convertibles. Rounds are priced on it.
- Option pool shuffle
- Expanding the employee pool inside the pre-money valuation, so the dilution falls on the existing holders and the new investor avoids it.
- Post-money SAFE
- A right to future shares that converts at the next priced round. The holder’s ownership is the investment divided by the post-money valuation cap.
- Conversion price
- The price that sets how many common shares each preferred share turns into. A lower conversion price means more common shares.
- Down round
- A funding round priced below the round before it.
- Anti-dilution protection
- A charter clause that lowers a preferred class’s conversion price after a down round, so it converts into more common.
- Full ratchet
- An anti-dilution form that resets the conversion price to the new, lower price, however many shares were sold. It gives a larger adjustment than a weighted average.
- Broad-based weighted average
- The common anti-dilution form. The conversion price moves by a formula that weighs the size of the new issue against all shares outstanding, options included.
- Pro rata right
- A contractual right to buy into later rounds in proportion to an existing holding, so the percentage can be kept.
Questions About Share Dilution
No. If new shares sell above the price you paid, your smaller percentage can be worth more than before. Share dilution costs you value in a down round, when new shares sell cheaper. It also costs you value when the money raised is spent without growing the company.
Divide your shares by the total after the round, counting every new share. That includes the investors’ shares, any pool top-up and any SAFEs or notes that convert. Your new percentage is your old one multiplied by one minus the round’s share of the post-round total. In the example above, 10% × (1 − 0.25) = 7.5%.
It is protection for a class of preferred stock, written into the company’s charter. It lowers that class’s conversion price if the company later sells shares more cheaply. The two main forms are full ratchet and broad-based weighted average.
Yes, exactly as it affects any holder of the class the vehicle owns. The vehicle’s share count is fixed, so its percentage falls when the company issues new shares. Whether any anti-dilution protection applies depends on the class the vehicle holds.
Where the Rules on This Page Come From
Rules and formulas were last checked on October 1, 2026. The dilution examples are illustrative and describe no real company. The weighted-average formula is quoted from a Delaware charter filed with the SEC. Actual charters vary, so read the one that governs your shares.
- 01US Securities and Exchange Commission, EDGAR2016Restated certificate of incorporation (Audentes Therapeutics) — broad-based weighted-average formula CP2 = CP1 × (A + B) ÷ (A + C)
- 02State of DelawareCurrent textDGCL §102(b)(3) — no preemptive rights unless granted in the certificate of incorporation
- 03State of DelawareCurrent textDGCL §151 — classes and series of stock and their rights
- 04Y CombinatorCurrent pagePost-money SAFE — YC standard since 2018; ownership sold equals investment divided by the valuation cap
- 05National Venture Capital Association10.2025Model legal documents — certificate of incorporation, stock purchase and investors’ rights agreements, updated October 2025
This page explains how a market works. It is not investment advice, not a recommendation of any security, strategy or company, and not an offer to sell or a solicitation to buy anything. Private companies may never list or be acquired, positions in them can be illiquid for years, and the entire amount invested can be lost. Figures are accurate as of the dates shown and change. Requirements for investor status, and the tax treatment of a private holding, differ by jurisdiction — the jurisdiction is named wherever this page discusses either. Prepared by the AXEVIL Capital research team.
What closed on the private market in the past two weeks
The rounds that priced, the tender offers that opened and the listings that filed — with the structure of each deal and the date on every figure. Written by the team that reads the paperwork.
Where to go from here
Cap tables & term sheetsWhat Is a Cap Table? Definition, How It Works and ExamplesA cap table lists who owns what in a company: every share class, option and convertible, before and after each round. How to read one, with a worked example.
Pre-IPO basicsWhat Are Pre-IPO Shares? Unlisted Equity ExplainedPre-IPO shares are stakes in a private company whose stock does not trade on an exchange. Types, who holds them, how they change hands and how they are priced.
ValuationWhat Is a 409A Valuation? Definition, How It Works and ExamplesA 409A valuation is an independent appraisal of a private company’s common stock. It sets the price employees pay for stock options. Rules and an example.