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Business Calculators

Startup Dilution Calculator

Use this startup dilution calculator to estimate how an investment and option pool change ownership percentages.

Reviewed May 25, 2026EstimateFormula shown

Quick answer

Startup Dilution Calculator: what it calculates

Startup Dilution Calculator calculates ownership after dilution from pre-money valuation, investment amount and option pool increase. The core method is Investor ownership = investment / (pre-money valuation + investment).

ResultOwnership after dilution
InputsPre-money valuation, Investment amount, Option pool increase, Current ownership
FormulaStartup dilution formula

Live calculator

Startup dilution

Investor ownership15.79%

$9,500,000.00 post-money valuation.

Ownership after round54.74%

Current ownership after investor dilution.

After option pool49.26%

15.74% total point reduction from current ownership.

Simplified cap table math

This does not model liquidation preferences, SAFEs, convertible notes, pro rata rights, anti-dilution terms, or pre-money option pool negotiation details.

Formula

Startup dilution formula

Investor ownership = investment / (pre-money valuation + investment)

This simplified calculator does not model SAFEs, notes, preferences, pro rata rights, anti-dilution clauses, or detailed cap table terms.

How to use

Steps

  1. Enter pre-money valuation.
  2. Enter investment amount.
  3. Add any option pool increase.
  4. Enter current ownership percentage.
  5. Review investor ownership, post-money valuation, and ownership after dilution.

Example

Sample calculation

Pre-money valuation$8,000,000
Investment$1,500,000
Investor ownership15.79%

Calculator use

Best for

  • Use this startup dilution calculator to estimate how an investment and option pool change ownership percentages.
  • Checking startup dilution formula with the formula and assumptions visible.
  • Comparing the result with the sample calculation and benchmark table before using it elsewhere.
  • Pricing, runway, cash flow, or work assumptions before an operating decision.

Before relying on it

Check first

  • Using the ownership after dilution without confirming that pre-money valuation, investment amount and option pool increase describe the same real-world case.
  • Ignoring that this simplified calculator does not model SAFEs, notes, preferences, pro rata rights, anti-dilution clauses, or detailed cap table terms.
  • Relying on the number without checking whether the visible assumptions match the real-world task.
  • Mixing cash and accounting profit, or monthly recurring items and one-time items.

Benchmarks

How to read the result

The calculator is a decision aid, not a fixed rule. Use the output to compare scenarios and document your assumptions. Benchmark ranges are broad planning heuristics unless this page names a specific source for the range.

Small roundLower dilution

A broad planning signal when investment is small relative to valuation.

Large roundHigher dilution

Investment size, valuation, and pool expansion all change ownership.

Option poolCheck timing

Whether the pool is created pre-money or post-money can materially change dilution.

Calculator accuracy

Methodology and assumptions

The formula, inputs, example, and limitations are shown so the result is checkable, not just a number in a box.

Formula

Investor ownership = investment / (pre-money valuation + investment)

Inputs used

Pre-money valuation, Investment amount, Option pool increase, Current ownership

Limitations

Results are estimates for quick planning and should be checked before important financial, legal, tax, health, or business decisions.

Last reviewed

May 25, 2026

Cite this page

Toolkit Shelf. Startup Dilution Calculator. Retrieved May 25, 2026, from https://toolkitshelf.com/tools/startup-dilution-calculator

FAQ

Common questions

What is startup dilution?

Startup dilution is the reduction in ownership percentage when new shares, investor ownership, or option pools are added.

Is option pool dilution always calculated this way?

No. Option pool timing and negotiation terms matter. This calculator is a simplified planning estimate.

Does this replace a cap table model?

No. Use a detailed cap table model or legal/finance advice for actual fundraising terms.

Can this replace accounting or legal advice?

No. Business calculators are scenario tools. Contracts, taxes, payment timing, accounting treatment, refunds, and legal requirements can change decisions.

What should I do after using a business calculator?

Save the assumptions, compare a conservative scenario, and review the result with actual books, contracts, or an advisor before making a high-stakes decision.

Why might another calculator show a different result?

Different calculators may use different rounding, assumptions, default rates, formulas, or input timing. Compare the visible formula and inputs before relying on the number.