How to Evaluate Growth Stocks: Revenue, TAM, and the Rule of 40

Why Growth Stocks Are Different

Evaluating growth stocks requires a different framework than traditional value investing. Many fast-growing companies aren't profitable yet — they're investing aggressively in expansion. You can't use a P/E ratio when there are no earnings. Instead, growth investors focus on revenue growth rates, total addressable market, unit economics, and the Rule of 40.

Revenue Growth: The North Star Metric

For growth companies, revenue growth rate is the most critical metric. A company growing revenue at 40% per year is doubling in size every two years. Look for consistency — not just one great quarter, but sustained strong growth over multiple years. When growth begins to decelerate significantly below 20%, valuation multiples typically compress sharply.

Total Addressable Market (TAM): How Big Can It Get?

TAM defines the ceiling for a company's growth. A business with a $5 billion TAM can never become a $50 billion revenue company. Great growth stocks typically operate in massive, expanding markets. Be critical of management's TAM claims — look for credible independent evidence the market is as large as stated.

The Rule of 40: Balancing Growth and Profitability

Add the company's annual revenue growth rate to its operating profit margin. If the result is 40 or higher, the business is considered healthy. A company growing at 50% with a -15% margin scores 35 — below threshold. A company growing at 30% with 15% operating margin scores 45 — healthy. This balances both growth and profitability in one number.

Valuation: Price-to-Sales for Pre-Profit Companies

For companies with no earnings, price-to-sales (P/S) is the primary valuation tool. Context matters enormously — a P/S of 15x on a company growing 60% annually is very different from 15x on a company growing 10%. Dividing P/S by the growth rate (a PEG-style adjustment) helps normalize across different growth rates for useful comparison.