Cap Table Mechanics

How Dilution Compounds Across Funding Rounds

Silicon Fund Editorial Updated August 23, 2026 8 min read

Founders often think about dilution round by round: "this round costs me X percent." But dilution compounds. Each round dilutes the percentage set by every round before it, and each option pool top-up, SAFE conversion, and priced round all interact with each other in ways that are easy to underestimate without a proper model.

Dilution is a percentage of a percentage

When a company sells new shares, everyone who already held shares owns a smaller percentage of the company, because the total number of shares outstanding has grown. If a founder owns 100 percent before any outside capital and gives up 20 percent in a first round, they hold 80 percent. If the next round dilutes the company by another 20 percent, the founder doesn't drop to 60 percent, they drop to 80 percent of 80 percent, which is 64 percent. Each subsequent round dilutes what's left, not the original whole.

SAFEs add dilution that isn't visible until conversion

A stack of outstanding SAFEs represents future dilution that hasn't happened yet on paper, since SAFEs don't convert into shares until a triggering event occurs. This can create a real gap between what a cap table shows today and what it will show once every outstanding SAFE converts at the next priced round. Founders who don't model this in advance are sometimes surprised at how much smaller their post-conversion ownership looks compared to their pre-conversion cap table.

Option pool top-ups are a common, underestimated source

Investors in a priced round frequently require the option pool to be refreshed or expanded before the round closes, so there's enough equity available to hire the team the new capital is meant to fund. That expansion is usually carved out of the pre-money valuation, which means the dilution from the pool top-up lands on existing shareholders, primarily founders, before new investor money is even added. This is one of the least visible but most consistent sources of founder dilution across financing rounds, and it directly interacts with how the option pool and vesting are structured going forward.

The round you're negotiating rarely dilutes you by the number in the term sheet alone. The pool top-up and the SAFE conversion sitting behind it usually cost more than the headline percentage.

Fully diluted ownership is the number that matters

A cap table that only shows currently issued shares understates real ownership dynamics. Fully diluted ownership accounts for everything that could become shares: all outstanding options (vested and unvested), any warrants, and every SAFE or convertible note as if it had already converted. This is the number serious investors calculate during due diligence, and it's the number founders should be tracking themselves, not just the simpler "shares issued today" view.

A simplified example of compounding

Consider a founder who starts at 100 percent ownership. A pre-seed SAFE round eventually converts and costs 15 percent of the company. A subsequent option pool top-up for the seed round costs another 10 percent of what remains. The priced seed round itself costs a further 20 percent. None of these percentages simply add up to 45 percent; each one is applied to what's left after the previous one, compounding down through the company's history. This is exactly why what founders retain in an exit depends on the full sequence of dilution events, not just the size of the most recent round.

How to actually track it

• Maintain one current, fully diluted cap table model, not a static snapshot that gets manually rebuilt each time an investor asks.
• Model every outstanding SAFE's conversion at a range of plausible future valuations, not just the current round's expected price.
• Include the expected size of a future option pool top-up when projecting what a new round will actually cost, not just the new investor's stated check size.
• Revisit the model after every grant, SAFE, or round, not only when preparing for the next fundraise.

Dilution is a normal, expected part of raising outside capital, and it isn't inherently bad: a smaller slice of a much larger, well-capitalized company can still be worth considerably more than a larger slice of a company that never raised the capital it needed to grow. The goal isn't to avoid dilution, it's to understand exactly how it compounds so there are no surprises when the next round, or the next exit, actually happens.