Quick guide
How to use this calculator
- Gather Existing holder shares, Pre-pool fully diluted shares, and New option-pool shares for the same business scenario before calculating.
- Keep pre-money and post-money values, cash and non-cash expenses, current and fully diluted ownership, and one-time versus recurring flows distinct.
- Apply the displayed option pool dilution result to the stated decision only after checking every entered assumption.
Calculation method
Calculation method
Post-pool ownership = existing holder shares ÷ (pre-pool shares + new pool shares).
The calculation uses these named inputs: Existing holder shares, Pre-pool fully diluted shares, and New option-pool shares. No market rate, benchmark, tax rule, or accounting classification is inserted automatically.
Fixed-decimal arithmetic remains exact through display unless a result is explicitly labelled approximate, such as a square-root inventory quantity.
Startup runway and fundraising
Where the Option Pool Dilution Calculator helps
Estimate existing-holder dilution from creating or expanding an option pool.
Use the result to make an entered cash, burn, dilution, valuation, or fundraising scenario explicit for discussion.
- Prepare a board cash scenario
- Compare financing terms on the same capitalization basis
- Test how hiring or revenue timing changes runway
Interpretation check
How to audit the result
Recalculate the scenario when any of these inputs changes: Existing holder shares, Pre-pool fully diluted shares, and New option-pool shares.
Keep this formula beside the result: Post-pool ownership = existing holder shares ÷ (pre-pool shares + new pool shares). Then compare the output with the source records and the calculator-specific assumption below.
- Confirm that all amounts use one currency and reporting period.
- Check that rates, counts, and quantities describe the same population or transaction set.
- Save the entered assumptions with the decision; the result alone is not reproducible evidence.
Worked example
Worked example
A holder with 600 of 1,000 shares before a 200-share pool moves from 60% to 50%.
Post-pool ownership = existing holder shares ÷ (pre-pool shares + new pool shares).
Supported inputs
Precision and limits
Visible input limits
Fixed decimals accept up to 30 digits and 12 decimal places and are capped at an absolute value of 1e12 per input. Rates are capped at 1000%; percentage shares and method-specific domains may be narrower.
International scope
No currency, tax jurisdiction, accounting framework, payroll rule, marketplace fee schedule, financing term, or industry benchmark is selected automatically.
Decision boundary
Use the result to make an entered cash, burn, dilution, valuation, or fundraising scenario explicit for discussion. Results remain arithmetic scenarios, not accounting records, forecasts, valuations, legal interpretations, professional advice, or recommendations.
Calculator-specific assumptions
This is a scenario from visitor-entered values. Keep currencies, periods, accounting classifications, and operating definitions consistent. It is not accounting, tax, legal, investment, or business advice.