How It Works
This calculator works in 4 steps.
Enter the shares held
Type the holder's share count.
Enter the total shares outstanding
Type the share count before the issuance, on the basis the user chooses (outstanding or fully diluted).
Enter the new shares issued
Type the number of new shares in the issuance.
Read the results
The calculator returns ownership before and after, the point change, and the relative dilution.
The Formula
The formula divides the holder's shares by the new total share count.
O₁ = S_h / S_totalO₂ = S_h / (S_total + S_new)D = 1 − O₂ / O₁ = S_new / (S_total + S_new)- S_h:
- Shares held by the holder
- S_total:
- Shares before issuance
- S_new:
- New shares issued
A holder of 500,000 of 4,000,000 shares owns 12.5%. After 1,000,000 new shares, ownership is 500,000 / 5,000,000 = 10%, a relative dilution of 20%.
Conversion Table
The conversion table gives ownership before and after issuance for 6 share scenarios.
| Shares held | Shares before | New shares | Ownership before | Ownership after | Relative dilution |
|---|---|---|---|---|---|
| 1,000,000 | 10,000,000 | 2,000,000 | 10% | 8.333% | 16.7% |
| 500,000 | 4,000,000 | 1,000,000 | 12.5% | 10% | 20% |
| 2,500,000 | 10,000,000 | 2,500,000 | 25% | 20% | 20% |
| 100,000 | 1,000,000 | 250,000 | 10% | 8% | 20% |
| 3,000,000 | 8,000,000 | 500,000 | 37.5% | 35.29% | 5.88% |
| 50,000 | 20,000,000 | 5,000,000 | 0.25% | 0.2% | 20% |
What Is the Share Ownership Dilution Calculator?
The Share Ownership Dilution Calculator is a tool that returns a shareholder's ownership percentage after a company issues new shares. Ownership falls when the share count grows and the holder's share count stays the same.
Equity dilution follows the same arithmetic as chemical dilution: the holder's shares stay constant while the total grows. A holder of 1,000,000 out of 10,000,000 shares owns 10%; after 2,000,000 new shares, that holder owns 8.33%. The calculator returns ownership before and after, the percentage-point change, and the relative dilution. Results are arithmetic only and are not financial or legal advice.
Common Uses
There are 5 main uses of this calculator.
Founder planning
Founders see ownership after each planned issuance.
Employee equity
Employees estimate how new rounds affect their grants.
Secondary offerings
Investors estimate dilution from public follow-on offerings.
Board review
Boards compare issuance sizes before approval.
Investor education
Students learn how share issuance changes ownership.