Cap Table, SAFE & Convertible Note Dilution Waterfall (Excel)

Description
Three facts in a priced round depend on each other at the same moment. The price per share is the pre-money valuation divided by the fully diluted share count. The shares issued to a discounted SAFE or note depend on that price per share. The option pool top-up is sized as a percentage of the post-round total, which includes both of the above.

Written straight into a spreadsheet that is a circular reference, and Excel refuses to calculate it until you enable iterative calculation - a setting that travels with the file on some machines and not others, that changes the answer depending on the maximum-iterations value, and that a diligence reader is entitled to distrust.
Most cap table templates avoid the problem by ignoring it. They price the round off the pre-round share count, which overstates the price per share and understates founder dilution, every time.

This workbook puts the loop on the page. The Conversion Engine tab solves it across twelve visible columns with a residual you can watch fall to zero, and an integrity check confirms it converged. Iterative calculation is never touched.

WHAT IT HANDLES
Post-money SAFEs converting at their cap to a fixed percentage of the company - the standard YC behaviour, solved in closed form. Pre-money SAFEs converting at the better of cap price and discount, with the winning leg shown. Convertible notes with accrued interest. Uncapped and MFN instruments. The option pool shuffle, created before or after the round. And an exit waterfall with liquidation preference, participation and caps.

THE WORKED EXAMPLE
Three founders, a one million share pool, six SAFEs, two notes, and a six million dollar round at a twenty million pre-money. Price per share settles at 1.6666, post-money at twenty-six million, and the founders go from 88.9% to 51.3% - a thirty-eight point drop that no pre-round calculation would have shown them.

TWELVE INTEGRITY CHECKS
Every one must read PASS before you quote a number: the iteration converged, price per share times the pre-money share count equals the pre-money valuation, every holder's shares sum to the fully diluted total, the pool lands exactly on its target percentage, each converting dollar buys exactly the shares its own price implies, and seven more.

Live formulas throughout. No macros, no add-ins, no external links, no password protection, no locked cells. Opens identically in Excel, LibreOffice, Numbers and Google Sheets.

This workbook models the arithmetic of your own cap table. It is not legal or investment advice.