Tracking founder and early-investor ownership as a biotech raises Seed, Series A, B, and C — and where an option pool refresh quietly bites everyone
Every capitalization table begins the same way: at incorporation, the entire equity of the company — 100% of it — is split between the founders and, almost always, an initial option pool set aside to attract the first employees. Everything that happens afterward, across every future financing round, is a story about how that original 100% gets divided among an ever-growing list of stakeholders.
A capitalization table (cap table) is simply a ledger: who owns what percentage of the company, expressed in shares, and how that ownership is expected to change as new securities are issued. At founding it is trivially simple — a small number of rows, usually just the founders and a reserved option pool, summing to 100%. The complexity that makes cap tables notoriously hard to reason about arrives only once financing rounds begin issuing new share classes, each carrying its own price, its own preferences, and its own effect on everyone else's percentage.
A critical early distinction is between basic share count and fully-diluted share count. Basic shares are what has actually been issued and is currently outstanding. Fully-diluted shares add in everything that could be issued in the future: the entire authorized option pool (not just options already granted), outstanding warrants, and any convertible instruments assuming their conversion. Ownership percentages quoted casually almost always mean the fully-diluted number, because that is the figure that matters at an exit — but the two numbers can diverge meaningfully, and confusing them is one of the most common errors non-specialists make when reading a cap table.
The option pool is equity carved out of the founders' ownership and reserved, unallocated, for future employees, advisors, and consultants. It is typically sized as a percentage of the fully-diluted cap table — commonly 10–20% at founding, sometimes smaller and grown later — and its purpose is straightforward: a startup competing for engineering, scientific, and commercial talent against larger, better-resourced companies needs equity compensation as a lever, and that equity has to come from somewhere before any revenue exists to fund cash bonuses.
The size of the option pool matters far beyond the initial round. Because investors in every subsequent financing round will insist the pool be large enough to cover several years of anticipated hiring, and because — as later sections show — that pool is frequently refreshed pre-money at each new round, the option pool functions as a recurring, compounding source of dilution that is easy to underestimate if a founder only tracks the percentages associated with named investors.
A useful mental model: founders do not really own "90%" of the company at founding if a 10% option pool sits alongside them — they own 90% of a pie that already has a slice permanently reserved for people who have not been hired yet. Every option granted from that pool, once vested and exercised, converts into real, counted shares.
The Seed round is usually the first time outside capital enters the cap table, and it introduces the mechanic that governs every subsequent round: new investors receive newly issued shares in exchange for cash, and because the total number of shares outstanding grows, every existing shareholder's percentage ownership falls — even though the number of shares they personally hold has not changed at all.
Dilution is pure arithmetic, and understanding it precisely removes most of the mystery around cap tables. A company agrees on a pre-money valuation — what it is deemed to be worth before the new investment — and investors put in a specific dollar amount. Post-money valuation is simply pre-money plus the new investment. The percentage the new investors receive equals their investment divided by the post-money valuation, and every existing shareholder's stake is multiplied by (1 − new investor percentage) to reflect the larger share count now outstanding.
Critically, dilution does not reduce the number of shares any existing holder owns — a founder with one million shares before the round still has exactly one million shares after it. What changes is the denominator: the total shares outstanding grows to make room for the new investors' shares, so that same one million shares now represents a smaller slice of a larger whole. This is why cap table conversations are conducted in percentages and share counts simultaneously — the share count tells you what you actually hold; the percentage tells you what that holding is worth relative to the whole company at any given moment.
In a "clean" round with no pool refresh and no special protections, every existing shareholder is diluted by exactly the same percentage: if new investors take 20% of the post-money company, founders and the existing option pool both shrink by multiplying their pre-round percentage by 0.80. This proportionality is not a law of nature — it is the default outcome only when no other mechanic intervenes. The two mechanics that most commonly break this simple proportionality are an option pool refresh (Stage 3) and pro-rata investment rights (Stage 4), both of which redistribute dilution unevenly across the cap table rather than spreading it evenly.
Biotech Seed rounds carry a distinctive feature worth noting: because the "product" being funded is often a preclinical asset years from any revenue, valuations are driven less by traditional metrics (revenue multiples, comparable transactions) and more by the strength of the underlying science, the experience of the founding team, and the size of the addressable indication — making Seed-stage biotech valuations both higher-variance and more negotiation-dependent than in many other sectors.
A Seed round diluting founders from 90% to roughly 72% is not a sign anything went wrong — it is the mechanical, expected consequence of trading equity for the capital needed to fund the next several years of R&D. The number to watch is not the dilution itself but whether the capital raised is buying enough value-creating progress to justify it.
Series A is where most founders first encounter the "option pool shuffle" — a widely used but frequently misunderstood negotiating mechanic in which the option pool is topped up before the new investment is priced, so that existing shareholders, not the incoming investors, bear the cost of refilling it.
When a new investor negotiates a Series A term sheet, they typically require that the option pool be topped up to a target size — say, 15% of the fully-diluted post-money cap table — before their investment is priced. Because this top-up is structured as a pre-money event, the additional pool shares dilute the pre-money shareholders (founders and existing investors) exactly as if it were a separate, earlier financing round, before the new investor's percentage is even calculated.
The consequence is that the new investor's stated pre-money valuation is not quite what it appears to be. If a term sheet offers a $30M pre-money valuation but also requires a fresh 15% option pool carved out of that pre-money value, the founders are effectively receiving a lower true valuation for their shares than the headline number suggests — the pool refresh is, in economic substance, a valuation discount that happens to be denominated in dilution rather than in dollars.
From the investor's perspective, the pool refresh is defensible: a growing biotech genuinely will need meaningful equity compensation to hire the clinical, regulatory, and manufacturing talent required to advance a pipeline, and an investor does not want their own new investment diluted by option grants issued after they invest — they would rather that dilution be absorbed by the existing cap table before their money comes in. From the founder's perspective, the right response is not to reject pool refreshes outright (they are close to a market standard at priced rounds) but to negotiate the size of the pool actively, sized realistically to the actual hiring plan for the specific period until the next round, rather than accepting a round, padded number by default.
The practical negotiating lever is to model the hiring plan in detail — roles, timing, typical grant sizes by seniority — and argue the pool size down to what is actually needed, since every percentage point of unnecessary pool size is a percentage point of avoidable founder dilution. Sophisticated founders and their counsel will often present this hiring-plan model directly to the new investor as the basis for the negotiated pool size.
The single most important number to negotiate at Series A is often not the price per share or the headline valuation — it is the size of the pre-money option pool refresh, because it dilutes only the existing cap table and is frequently glossed over in term sheet discussions that focus on valuation as if it were the whole story.
As a company matures into Series B and Series C, dilution continues with every new round — but the cap table also starts to show the effect of pro-rata rights, contractual provisions negotiated by earlier investors that let them invest again in later rounds specifically to defend their existing ownership percentage against further dilution.
A pro-rata right, typically negotiated into the preferred stock terms of a Seed or Series A investment, gives that investor the option — not the obligation — to purchase enough shares in each future financing round to maintain the ownership percentage they held immediately before that round. It does not grant them extra shares beyond what is needed to hold their position steady; it simply gives them the standing right to participate rather than being forced to negotiate access to a hot round after the fact.
Exercising a pro-rata right requires real, additional capital at every subsequent round — an investor who put in $2M at Seed to get 8% may need to write meaningfully larger checks at Series B and Series C just to keep that same 8%, since later rounds are priced at higher valuations. This is precisely why pro-rata defense is described as "partial": an investor without a follow-on capital reserve, or a fund strategy that deliberately caps follow-on investment, will let their percentage dilute like everyone else's even if the contractual right to defend it exists.
Because pro-rata participation is selective — some investors exercise it fully, some partially, some not at all, and founders and the option pool essentially never have a pro-rata right of their own — later-round dilution is not spread evenly the way a clean Seed round is. Investors who exercise pro-rata rights are diluted less than the round's stated new-money percentage would otherwise imply; investors and founders without that protection absorb correspondingly more of the round's dilutive effect to make the arithmetic balance.
This creates a structural pattern across financing rounds: the earliest, highest-conviction investors — the ones most likely to have both the contractual right and the capital reserve to exercise it — tend to see their ownership percentage decay more slowly across the company's life than a purely proportional model would predict, while founders, who almost never have an equivalent right, see their percentage decay at something closer to the full, undefended rate at every single round.
Pro-rata rights are one of the main reasons two rounds with an identical headline dilution percentage can produce very different cap tables in practice — the identity of who exercises their pro-rata right, and how fully, determines exactly whose ownership absorbs the difference.
At exit — an acquisition or an IPO — the fully diluted cap table is finally settled: every option, warrant, and convertible instrument is accounted for, and the resulting percentages determine exactly how the proceeds of the exit are distributed. Founders who started at 100% frequently end up owning somewhere in the 10–30% range — and, for a well-executed company, that outcome is still usually a very good one.
The single most important intuition for interpreting an exit cap table is that percentage ownership and dollar outcome are not the same measurement, and only the second one pays anyone's bills. A founder holding 90% of a company worth $5M at incorporation and a founder holding 18% of the same company, now worth $400M at exit after four financing rounds, is the same person on the same journey — and the second number is worth roughly eighteen times more in absolute dollars despite representing a fraction of the original percentage.
This is why experienced operators evaluate a financing decision not by asking "how much will I be diluted" in isolation, but by asking whether the capital being raised is expected to increase the company's value by more than the dilution costs — a well-priced round that meaningfully de-risks a clinical program or unlocks a much larger addressable market can be strongly value-accretive to founders even though their percentage ownership falls, precisely because it is expected to grow the size of the pie by more than it shrinks their slice of it.
At exit, every previously unexercised option in the pool, every warrant, and every outstanding convertible note or SAFE converts (or is deemed to convert) into common or preferred stock, and it is this fully-diluted share count — not the basic, currently-outstanding share count — that determines each party's actual share of the proceeds. This is also the moment liquidation preferences are triggered: preferred stockholders from later rounds typically have the contractual right to receive their original investment back (often 1x, non-participating, in a clean structure) before common stockholders — including founders — receive anything, meaning that in a modest or "soft" exit, the fully-diluted percentage on paper can overstate what founders and common shareholders actually receive once preference stacks are paid out first.
Understanding this distinction — basic vs. fully-diluted shares, and ownership percentage vs. actual proceeds after liquidation preferences — is the final and most consequential piece of cap table literacy: the donut chart of ownership percentage tells a founder how the pie is sliced, but the waterfall of who gets paid in what order, at what preference multiple, tells them what each slice is actually worth when the company is finally sold.
The complete arc — from 100% of a company with no proven value, through successive rounds each trading a slice of ownership for capital and validation, to a much smaller percentage of a company that is, if all goes well, worth vastly more — is not a story of founders losing control of their company. It is the standard, expected mechanism by which early, illiquid, high-risk ownership is converted into a real, liquid, and hopefully far larger outcome.
| Product | Indication | Trial Design | Key Result |
|---|---|---|---|
| Founding | |||
| Seed | |||
| Series A | |||
| Series B | |||
| Series C |