The calculation is straightforward: if a startup has a pre-money valuation of $4 million and receives a $1 million investment, the post-money valuation is $5 million. The new investors then own 20% of the company ($1 million divided by $5 million), while existing shareholders see their ownership diluted proportionally.
Why It Matters
Post-money valuation directly impacts your ownership stake and potential returns as an angel investor. A $100,000 investment at a $5 million post-money valuation gives you 2% ownership, while the same investment at a $10 million post-money valuation yields only 1% ownership—cutting your potential returns in half. Understanding this distinction helps you negotiate effectively and model your expected returns accurately. The post-money valuation also sets the benchmark for future funding rounds, influencing whether your investment appreciates or faces down-round dilution.
Example
Sarah wants to invest $250,000 in a SaaS startup. The founders propose a $3 million pre-money valuation. After Sarah's investment, the post-money valuation becomes $3.25 million, giving her 7.69% ownership ($250,000 ÷ $3,250,000). Two years later, the company raises a Series A at a $15 million post-money valuation. Sarah's stake, though diluted to approximately 6.2% after the new round, is now worth $930,000—a 3.7x return on her initial investment. If the founders had instead insisted on a $5 million pre-money valuation, Sarah would have owned only 4.76% initially, and her stake at the Series A would be worth significantly less despite the same company performance.