A cap table, short for capitalization table, is the record of who owns what in a company once equity has actually been issued. It lists every owner (founders, investors, and people holding stock options) and how much of the company each one holds.
Early on it can live in a single spreadsheet. As the company grows it becomes the authoritative source of truth for ownership, and keeping it accurate matters enormously.
It also moves. Every time the company raises money or grants equity, ownership percentages shift. That is dilution: new shares are created, each existing slice gets a little smaller, even as the whole pie usually gets bigger. A smaller slice of a much larger pie is the normal, healthy path of a growing startup, and the cap table is how you watch it happen.
Here is the part founders most often blur.
Before incorporation, there are no shares and no official cap table, because there is no company to own anything yet. What you have is an intended allocation: the founder split you agreed. It is the first draft of a cap table, not the real thing.
Keeping those two ideas separate is healthy. Before incorporation, founders may model an intended allocation. A real cap table starts when a company exists and equity is actually issued. Recording the intended split clearly now, alongside vesting, just means the eventual cap table formalises a deliberate decision rather than a rushed one.
Before the cap table, there is the founder promise.