Equity Dilution

Quick Definition

The reduction in existing shareholders' ownership percentage when new shares are issued.

What is Equity Dilution?

Equity dilution happens when a company issues new shares, reducing every existing shareholder's ownership percentage. Your share count stays the same, but the total pie gets bigger, so your slice gets smaller.

Dilution is a normal part of startup growth. Every funding round, option pool increase, and convertible instrument conversion creates dilution. The question isn't whether you'll be diluted. It's how much.

Why Dilution Matters

A founder who starts at 100% might own 30-40% by Series A and 10-20% by Series C. Each round chips away at ownership. The goal is to make sure the value of your smaller percentage grows faster than the percentage shrinks.

Owning 15% of a $500M company ($75M) beats 80% of a $5M company ($4M). Dilution is worth it when it funds real growth.

Common Sources of Dilution

• Priced equity rounds (Series Seed, A, B, etc.)
• Option pool creation or expansion
• SAFE and convertible note conversions
• Warrant exercises
• Anti-dilution adjustments for prior investors

Formula

Dilution % = New Shares Issued ÷ (Existing Shares + New Shares Issued)
Post-Dilution Ownership = Original Ownership × (1 - Dilution %)
Or more directly:
Post-Dilution Ownership = Your Shares ÷ New Total Shares

Example

Founder owns 5,000,000 of 10,000,000 total shares (50%).
Series A investor buys 2,500,000 new shares.

• New total shares: 12,500,000
• Founder's new ownership: 5,000,000 ÷ 12,500,000 = 40%
• Dilution: 50% - 40% = 10 percentage points (or 20% relative dilution)

If the company also creates a 10% option pool (1,250,000 shares) from pre-money:

• New total shares: 13,750,000
• Founder's ownership: 5,000,000 ÷ 13,750,000 = 36.4%

The option pool added another 3.6 percentage points of dilution on top of the round itself.

Related Terms

Anti-Dilution
Protection that adjusts an investor's share price if the company later raises money at a lower valuation.
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Option Pool
A percentage of company equity reserved for future employee stock option grants, typically 10-20% of fully diluted shares.
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Preferred Stock
A class of stock with special rights including liquidation preference and anti-dilution protection, typically held by investors.
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