Ownership dilution.

Equity dilution calculator measures ownership reduction from new share issuance. Holding 100,000 shares at company with 1M total. Company issues 200,000 new shares: total now 1.2M. Your share = 100,000 / 1.2M = 8.3%. Dilution = (200k / 1.2M) = 16.7%. Your ownership decreased from 10% to 8.3%.

Sources of dilution: (1) Funding rounds (new investor shares). (2) Employee stock option exercises. (3) Convertible note conversions. (4) Warrant exercises. (5) Acquisitions paid in stock. Each issuance dilutes existing shareholders proportionally. Track 'fully diluted' ownership (assuming all options/warrants/converts exercised) for accurate picture.

Anti-dilution protections (in preferred stock): allow investor to maintain ownership % through additional shares at reduced price during down rounds. Standard for VC investments. Common stock holders (founders, employees) typically have NO anti-dilution protection - bear full dilution impact. Always model dilution impact when joining startup as employee or investor: significant difference between 0.5% on hire and 0.2% at IPO is the dilution journey.

A worked example

Try the defaults: your current shares of 100,000, new shares issued of 200,000, current share price of 10. The tool returns 66.67%. You can adjust any input and the result updates as you type — no submit button, no reload. That's the real power here: seeing how sensitive the output is to one or two assumptions.

What moves the number most

The result responds to Your Current Shares, New Shares Issued (Total), and Current Share Price. Not every input has equal weight. Flip one at a time toward extreme values to feel which ones move the needle most for your situation.

The formula behind this

Dilution % = new shares / (current + new shares) × 100. Everything the calculator does is shown in the formula box below, so you can check the math against your own spreadsheet if you want.

Using this well

Treat the output as one point on a wider map. Run it three times — a pessimistic case, a central case, and a stretch case — and plan against the pessimistic one. That habit alone separates people who stick with an investment plan from those who bail at the first wobble.

What this doesn't capture

Steady-rate math ignores real-world volatility. Actual returns are lumpy; sequence-of-returns risk matters most in drawdown; fees and taxes drag on compound growth; and behaviour changes in drawdowns can reduce outcomes below the projection. Treat the number as one scenario, not a forecast.