Understanding how to calculate and present Total Addressable Market (TAM) is crucial for startups during investor conversations.There are two popular approaches to building a TAM: top-down and bottom-up, each with their own advantages and disadvantages.Top-down TAM involves taking the total market size and estimating your share of the market based on analyst firm forecasts.Bottom-up TAM pulls from your existing customers and sales, providing more credibility, but requires more data.