How dilution actually stacks across rounds.

Founder dilution at any single round looks manageable. Carta's median Series A dilution was 17.9% in Q1 2025 and its Series B median 12.9% across 2025, with the median from seed to Series C at about 16%. But rounds multiply rather than add, and any option pool refresh comes on top. In the worked example below, a solo founder ends Series B owning 41%. The math is mechanical, which is why it is worth modelling before the first term sheet rather than after.

Worked example: solo founder to Series B

Solo founder starts with 100% of the company at incorporation. The pre-money figures below are round numbers chosen so the arithmetic stays legible, not the 2026 medians, which are on the benchmarks table, and they are higher at Series A and B than this example. What carries across is the shape: the percentages depend on the ratio of round size to post-money, not on the absolute level, so a company raising at twice these valuations and twice these round sizes ends up in the same place.

Solo founder ends Series B at 41% ownership. The math here is for a single founder; co-founder teams start at smaller percentages and end correspondingly lower. A two-founder team with a 50/50 split at incorporation ends Series B at roughly 20.5% each.

The option pool is the silent dilution

Every funding round refreshes the option pool. The refresh comes out of pre-money allocation, not post-money, which means it dilutes founders, not the new investor. In the seed step above, the pool top-up costs the founder about 6 points of ownership before the investor takes anything, and none of it funds the business.

What founders can negotiate

1. Option pool sizing. Size the pool to a documented hiring plan for the period the round funds, and negotiate from that plan rather than from the investor's opening number.
2. Pool source (pre vs post). The default is pre-money pool refresh (dilutes founders). Negotiate for a portion to come post-money (dilutes the new investor too). This is rare but achievable when the round is competitive.
3. Pre-money valuation itself. Higher pre-money = lower founder dilution per dollar raised. The dilution percentages above scale linearly with the inverse of pre-money.
4. Round size. Smaller round = less dilution but more frequent fundraising. Balance against the operating runway you actually need.

Practical recommendation: Build a cap-table spreadsheet that projects 4 rounds out before you start fundraising. Knowing your projected Series B ownership when you sign the Pre-seed term sheet changes how you negotiate option pools and pre-money. Founders who only model the current round routinely arrive at Series B owning less than they expected.