Software businesses operate on a different financial logic than traditional companies. Most of the cost is upfront: research, development, and building the initial product. Once the software is built, the cost to serve one more customer is often close to zero. This creates immense operating leverage—as revenue grows, profits can grow much faster because the costs don't scale at the same rate. The result is typically high gross margins, often in the 70-80% range, which is the engine of value creation.

This structure, however, has a hidden vulnerability: a deep sensitivity to interest rates. Because so much of a software company's value is tied to profits expected far in the future, their present value is highly dependent on the discount rate used to pull those future cash flows back to today. This discount rate is often the Weighted Average Cost of Capital (WACC), which is directly influenced by prevailing interest rates. When rates rise, the WACC increases, and the present value of those distant, high-margin profits shrinks significantly.

While high gross margins are attractive, they don't guarantee success. The other side of the coin is the cost of growth. In software, this is captured by the relationship between two key metrics: Lifetime Value (LTV) and Customer Acquisition Cost (CAC). LTV represents the total revenue a business can reasonably expect from a single customer account throughout their relationship. CAC is the total cost of sales and marketing efforts needed to acquire a single new customer.

A high LTV:CAC ratio is great, but it's only half the story. The time it takes to recover the CAC, known as the payback period, is also critical. A company might have a fantastic 5:1 ratio, but if it takes 36 months to recoup the initial acquisition cost, the business will require enormous amounts of capital to fund its growth.

This brings us to a widely used heuristic for evaluating the health of a SaaS company: the Rule of 40. It provides a simple framework for balancing growth with profitability. The rule states that a healthy software company's annual revenue growth rate plus its profit margin should equal or exceed 40%.

For example, a company growing at 60% annually with a -20% profit margin passes the test. So does a company growing at 15% with a 25% profit margin. In a low-interest-rate environment, investors heavily favoured growth, sometimes overlooking deep losses. However, in the current macroeconomic climate, with a higher cost of capital, the preference has shifted. Profitability and efficient growth are now prized, and companies are under more pressure to demonstrate a clear path to positive cash flow.

Understanding these mechanics—high operating leverage, sensitivity to capital costs, LTV:CAC ratios, and the balance between growth and profit—is key to accurately valuing software businesses.