Seed to Series B: A Founder's Stake Can Shrink to 65% of Its Starting Size Before Any Option Pool Refresh

We ran the 2026 median deal terms through three rounds and a 100% stake fell to 65.6%

Starting from a 100% stake, a $2M seed round at an $18.4M pre-money valuation (2026 median) dilutes to 90.2%. Layer on an $8M Series A at a $45M pre-money valuation and it drops to 76.6%. A $20M Series B at a $120M pre-money valuation brings it to 65.6% — worth roughly $91.9M at the Series B’s $140M post-money valuation. Three rounds, and a bit over a third of the original stake is gone to new investors — before any option-pool refresh is even considered.

That 65.6% figure is deliberately optimistic. Published survey data puts median founder retention at roughly 56% after seed alone, 36% after Series A, and 23% after Series B — all lower than this tool’s simplified math, because investors commonly require the option pool to be topped up from existing shareholders’ stakes as a condition of the round, on top of the raise itself. This tool shows the dilution from the raise; real dilution is usually worse.

How the math works

1. Post-money valuation = pre-money valuation + amount raised.
2. New investor share = amount raised ÷ post-money valuation.
3. Ownership after the round = ownership before the round × (1 − new investor share).
4. Stake value = ownership after the round × that round’s post-money valuation.

Sources: WaveUp Startup Dilution Benchmarks (2026) for median round sizes, pre-money valuations, and dilution percentages by stage; CRV’s public equity-dilution research for the founder-retention-by-stage figures cited above.

The honest limit: real cap tables are more complicated than sequential pro-rata dilution. Option-pool refreshes, pro-rata rights, anti-dilution provisions, and convertible-note conversion mechanics all affect the real number — this tool is a planning-level illustration of the base mechanic, not a substitute for a real cap-table model before signing term sheets.

Math runs locally. Inputs never leave your browser. Source on github.

Where this calculation doesn’t apply

• Your round includes an option-pool refresh. This is the biggest gap between this tool and reality — investors commonly require a new or expanded option pool carved out of existing shareholders’ stakes before their money comes in, which dilutes founders beyond what the raise amount alone implies.
• You’re raising on a SAFE or convertible note. These convert into equity later, often at a discount or valuation cap, with mechanics this simplified priced-round model doesn’t capture.
• You have multiple co-founders with different individual stakes. Run this per-founder using each person’s own starting ownership percentage — the dilution multiplier applies equally to everyone, but the dollar and percentage-point outcomes differ by starting stake.
• Pro-rata rights or anti-dilution provisions apply. Some investors have contractual rights to maintain their percentage ownership in future rounds, or protection against down-round dilution — neither is modeled here.

What to actually do

1. Model your own actual round terms, not the defaults — pre-money valuation and raise amount vary widely by company and market conditions.
2. Ask your investors directly whether an option-pool refresh is a condition of the round, and if so, how large — then treat this tool’s output as an upper bound on your post-round ownership.
3. Before signing a term sheet, get a real cap-table model (many legal/finance tools exist specifically for this) that accounts for pool refreshes and any preference stack.
4. Revisit this after each actual round closes to track real dilution against what was modeled going in.