Equity Dilution Calculator
Estimate how a new share issuance affects ownership. Compare pre- and post-money ownership, see the new holder’s percentage, and calculate pro-rata shares needed to maintain your current ownership.
100% Client-Side Processing
All calculations happen in your browser. No cap table or financial data is sent to any server.
Current cap table
Your ownership input
Your pre-money ownership percentage
Dilution event
For an option pool increase or other reserve created at the same time
Enter your cap table and dilution event details above to see the results.
Assumptions:
- Dilution assumes you do not participate in the new issuance (no pro-rata exercise).
- Pro-rata shares to maintain ownership are calculated as: your shares × (new shares ÷ pre-money shares).
- Implied valuations use the price per share multiplied by share counts; actual valuations may differ based on liquidation preferences, participation rights, and other terms.
- Additional reserved shares (e.g., option pool) are treated as part of the post-money share count and dilute all existing holders proportionally.
- This calculator does not model SAFEs, convertible notes, or instruments with discounts/caps—those require separate conversion calculations.
Table of Contents
What is dilution?
Dilution happens when a company issues new shares and existing holders keep the same number of shares. Your share count stays the same, but your ownership percentage drops because the total share count increases.
This calculator assumes you do not participate in the new issuance. If you do, your post-money ownership can be higher (or unchanged) depending on how many shares you purchase.
How the calculator works
Ownership percentage
Ownership is calculated as (shares owned ÷ total shares).
Post-money shares
Post-money total shares are pre-money shares plus any newly issued shares and any additional reserved shares (like an option pool increase).
Pro-rata shares to maintain ownership
To keep the same percentage ownership, you would need to buy enough shares so your ratio stays constant. The calculator estimates this as: (pro-rata shares = your shares × (new shares ÷ pre shares)).
Frequently Asked Questions
Use fully diluted shares if you want to include all options, warrants, and other convertible instruments as if they were already shares. If you only use outstanding shares, you may understate the true dilution.
This is an optional input for shares created alongside the financing but not issued to the investor—commonly an option pool increase. These shares increase the total share count and can dilute existing holders too.
This calculator computes new holder ownership from the new shares created at the round price: (new shares ÷ post shares). If you're modeling a SAFE or convertible note with a discount/cap, the effective share price differs and the share count will change.