Concept

Pre-money vs post-money

Pre-money is company value before new capital; post-money is pre-money plus the check. Ownership is investment divided by post-money. Confusing the two is how founders celebrate a headline and give away an extra third of the company.

Where founders get this wrong

Treating a '$90M valuation' as interchangeable when pre vs post changes ownership by a full slice.
Pitching post-money language while investors model dilution on pre-money — and not catching the mismatch.
Skipping a simple ownership table before agreeing to the number in the room.