Founders end up owning far less of their company than they started with. The mechanics are straightforward arithmetic, though several details make the outcome less intuitive than it first appears.
New shares reduce everyone's proportion
Raising money issues new shares to investors. The existing shares are unchanged in number, so their share of a larger total is smaller.
Nothing is taken from existing holders directly. Their proportion falls because the denominator grew, which is why the effect is called dilution rather than transfer.
Whether that is good or bad depends entirely on what the company does with the money, since a smaller share of a larger business can be worth considerably more.
The option pool is usually created before the round
Companies reserve shares to grant to employees, and investors typically require that pool to be established or expanded as a condition of investing.
Where the pool is created before the new money is counted, the dilution falls on existing shareholders rather than being shared with the incoming investor.
This detail moves ownership meaningfully and is frequently negotiated separately from the headline valuation, which is why two offers at the same valuation can differ materially.
Convertible instruments dilute later
Early funding often uses instruments that convert into shares at a subsequent priced round rather than setting a valuation immediately.
Because conversion happens later, the dilution they cause appears at the next round and is sometimes larger than founders expected when the instrument was signed.
Discounts and valuation caps in those instruments increase the number of shares issued on conversion, which compounds the effect.
Preferences change what a percentage is worth
Investors usually hold shares with a preference entitling them to receive their investment back before other shareholders participate in a sale.
Ownership percentage therefore describes the split only above that threshold, and in a modest outcome the preference can consume most of the proceeds.
The number that matters is fully diluted
Counting only issued shares understates the position, because options, convertible instruments and reserved pools will all become shares eventually.
The fully diluted count includes them, and it is the basis on which valuations and per-share prices are calculated in practice.
Anyone assessing their own position needs that figure alongside the preference terms, since the two together determine outcomes far more than the percentage on its own.