Startup Equity Dilution
Calculator

When a startup raises money by issuing new shares, everyone who held shares before the round ends up owning a smaller percentage of the company — even though they still own exactly the same number of shares. This is called dilution. The math is straightforward: post-money valuation = pre-money + investment. The new investor's percentage equals investment ÷ post-money. All existing holders — founders, employees, previous investors — are diluted pro-rata by the same factor of (1 − new investor %).

Option pool top-ups are typically added before the round closes (the "pre-money option pool shuffle"). Investors require a certain pool size on a post-money basis, so the pool expansion is carved out of the pre-money cap table — meaning founders bear its full dilution, not new investors. This calculator follows that standard convention: enter the additional option pool percentage you're granting in a given round and it will be deducted from existing holders before new investors are added.

Dollar values shown are illustrative: founder's stake ($) = post-money valuation × founder %. This is your paper value at each round's price — not the proceeds you'd receive in a liquidation (which depends on preferences, participation rights, and other terms not modeled here). Use this tool to understand the ownership mechanics; work with your lawyer and investors for the full picture.