Free calculator · Venture & Startup Finance
Founder Dilution Across Rounds
Compounds founder ownership downward across successive financing events, multiplying retained ownership by one minus each round’s dilution. Inputs are the dilution percentages for the option pool, seed SAFEs, Series A, and Series B.
By Devon Coombs, CPA, MBA · Assistant Teaching Professor of Finance, Santa Clara University · Reviewed October 2026
From the author: Devon Coombs, CPA, MBA teaches finance at Santa Clara University and works with corporate teams on practical AI.
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How much ownership do founders keep after several funding rounds?
Multiply the ownership retained at each step. A 20% dilution means existing holders retain 80% of their previous stake. Adding dilution percentages together gives the wrong answer because each round changes the ownership base.
Interactive Tool
Founder Dilution Across Rounds
Founder ownership after all rounds
36%
started at 100%
Dilution compounds: each round's percentage is taken on a base that already includes every prior round, so a string of ordinary rounds carries founders from 100% to a minority stake faster than the individual numbers suggest.
Understand the numbers
A worked example, step by step
Start at 100% founder ownership. Enter 10% option-pool dilution, 10% seed dilution, 20% Series A dilution, and 15% Series B dilution.
This fixed teaching example is separate from your saved calculator inputs. Enter the assumptions above to reproduce it.
- After the option pool: 100% × 90% = 90%.
- After seed and Series A: 90% × 90% × 80% = 64.8%.
- After Series B: 64.8% × 85% = 55.08%.
Founders retain 55.08% collectively
What the result tells you
The founders collectively retain 55.08% of the modeled fully diluted ownership, assuming they do not buy additional shares. Individual cofounder stakes depend on their original split.
Assumptions to check
The inputs are incremental dilution at each step, not SAFE valuation caps or dollar investments. Actual SAFE conversion, option-pool top-ups, pro rata participation, and financing terms require a cap table. Ownership percentage alone does not determine voting control or exit proceeds.
Try one change
Change Series A dilution from 20% to 30%. Retained founder ownership becomes 48.195%. Consider both the ownership given up and what the new capital lets the company accomplish.
Test it in the calculator ↑Learn the concept
This calculator comes from the free Entrepreneurial Finance course, where the concept is taught with readings, worked examples, and practice questions.
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Built by Devon Coombs, CPA, MBA, Assistant Teaching Professor of Finance at Santa Clara University.