Dilution
Also known as Equity Dilution, Founder Dilution, Ownership Dilution
Dilution is the reduction in an existing shareholder's ownership percentage when a company issues new shares. The share count grows, the held shares stay constant, so the percentage falls. Priced rounds, option pool expansions, and SAFE or note conversions are the three common sources.
Formula
New Ownership % = Old Shares / (Old Shares + Newly Issued Shares)- Old Shares
- The holder's existing share count, unchanged by the new issuance
- Newly Issued Shares
- Total new shares issued in the event (priced round, pool top-up, or conversion)
- New Ownership %
- The holder's percentage after the new shares are outstanding
In depth
Dilution happens any time the share count grows and your share count does not. Three things grow the share count: a priced round (new preferred issued to investors), an option pool top-up (new common reserved for employees), and a SAFE or note conversion at a priced round (existing instruments convert into preferred at a discounted price). All three are mechanically the same: denominator goes up, your numerator stays put, your percentage falls.
The order in which dilution events stack matters. Option pool expansions almost always happen inside the pre-money valuation, so the cost lands on existing holders. SAFE conversions happen at the priced round, often at a cap well below the new round price, so each $1M of converting SAFE creates more shares than $1M of new money. Anti-dilution provisions on preferred can absorb dilution that would otherwise land on preferred and push it back onto common. The end result is that common stockholders, mainly founders and employees, see dilution roughly 1.3-1.5x the headline new-money percentage at a typical Series A with normal terms.
Why it matters
Dilution is the single biggest determinant of founder wealth at exit, and it compounds across rounds. Carta's 2025 Founder Ownership Report shows median founder ownership at 56.2% after seed, 36.1% after Series A, and 23% after Series B. A founder who raises five rounds before IPO routinely ends with 10-15% ownership even with strong execution.
For LPs and IC members, dilution math also drives ownership-target discipline: a fund that wants 15% ownership at exit on a company that will raise four more rounds needs to enter with closer to 25-30% to absorb the dilution stack, or commit to a substantial follow-on reserve to maintain pro-rata.
Worked example
A founder starts with 10,000,000 shares (100%). Track four rounds:
| Round | Pre-money | Raised | Post-money | New shares | Pool change | Founder % |
|---|---|---|---|---|---|---|
| Founding | n/a | n/a | n/a | 10,000,000 | 0% | 100.0% |
| Seed | $8M | $2M | $10M | 2,500,000 + 10% pool inside pre-money | +10% pool | 70.0% |
| Series A | $30M | $10M | $40M | 25.0% new round | no change | 52.5% |
| Series B | $80M | $20M | $100M | 20.0% new round | +2% pool top-up | 41.2% |
| Series C | $200M | $50M | $250M | 20.0% new round | no change | 33.0% |
After seed : 100% * (1 - 0.20 - 0.10) = 70.0%
After Series A : 70.0% * (1 - 0.25) = 52.5%
After Series B : 52.5% * (1 - 0.20 - 0.02) = 40.95% (round 41.2%)
After Series C : 41.2% * (1 - 0.20) = 32.9% (round 33.0%)
After four rounds, the founder holds 33% of a $250M company, or roughly $82.5M on paper. The starting 100% of a $1M company was worth $1M. The math works because per-share value rose faster than the ownership percentage fell. The math breaks for founders who raise too much, too fast, into option pools that compound, in down rounds where anti-dilution accelerates common-stock dilution.
Frequently asked
What is typical founder dilution per round?
Carta's data shows median Series A dilution of about 17.9% in Q1 2025, down from 20.9% a year earlier. Seed rounds dilute roughly 15-20%, Series A 15-20%, Series B 12-18%, and later rounds 10-15%. Cumulative founder ownership across stages: ~56% after seed, ~36% after Series A, ~23% after Series B, falling toward 10-15% by IPO for a typical founding team.
Is dilution always bad for founders?
No. Dilution is the price paid for capital, and the test is whether the per-share value grows faster than the percentage shrinks. A founder owning 100% of a $1M company who dilutes to 25% of a $100M company holds $25M instead of $1M. The math is bad only when round-over-round value growth lags the dilution rate.
How does the option pool create dilution?
Option pools are usually expanded inside the pre-money valuation, which means the dilution from the pool comes out of existing holders, not the new investor. Cooley GO calls this the option pool shuffle. A typical Series A might require a 10% post-close pool, which can transfer 5-8% of the company from founders and prior investors to the option pool with no new cash entering the company.
How do SAFEs and convertible notes dilute founders?
SAFEs and notes don't dilute until they convert. At the next priced round, they convert into preferred shares based on their valuation cap or discount, often at a much lower price than the new investors are paying. The resulting share count can be larger than founders expect, and the dilution lands entirely on common holders. Stacking multiple post-money SAFEs compounds this.
What is anti-dilution protection?
Anti-dilution adjusts preferred-shareholder conversion prices downward if the company later raises at a lower valuation (a down round). Broad-based weighted-average is the NVCA default and the market standard. Full-ratchet exists but is rare. Anti-dilution protects preferred from new-round dilution at the cost of additional dilution to common.