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Startup Dilution Calculator

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

Planning estimate

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.

Planning comparison only. Check estimates, omitted costs, timing, and constraints before making an operating decision.

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

  • Estimating business pricing, margin, retention, runway, dilution, revenue, or profitability before an operating decision.
  • Comparing base, conservative, and optimistic assumptions with the revenue, cost, churn, or payment timing visible.

Before relying on it

Check first

  • Mixing cash flow, accounting profit, bookings, revenue recognition, one-time fees, and recurring revenue.
  • Leaving out taxes, refunds, discounts, churn, payment delays, support cost, contractor cost, or owner time.
  • Using one optimistic case as the operating plan without checking downside assumptions.

Details

What to know before using the result

Scenario inputspre-money valuation, investment amount, and option pool increase

Keep pre-money valuation and investment amount aligned to the same scenario so ownership after dilution represents a consistent calculation.

Method checkStartup dilution formula

The tool applies Investor ownership = investment / (pre-money valuation + investment) to the entered values, then keeps ownership after dilution, examples, assumptions, and limits visible for review.

Benchmarks

How to read the result

Small round: Lower dilution.

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

Large round: Higher dilution.

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

Option pool: Check timing.

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

Calculator accuracy

Methodology and assumptions

Formula, inputs, limitations and review record
Formula

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

Inputs used

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

Limitations

Business results depend on contracts, accounting treatment, taxes, payment timing, refunds, collections, and operating assumptions.

Review record

Catalog QA baseline on June 6, 2026. This date marks the catalog-wide automated and editorial QA baseline, not a tool-specific expert review.

Cite this page

Toolkit Shelf. Startup Dilution Calculator. 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.