TAM slides are everywhere — and often wildly misleading. In this post, Angus Norton, founder of Bodhi Venture Labs, breaks down why total addressable market estimates are frequently inflated, misunderstood, or just plain wrong. Drawing from real-world experience at Microsoft and Xero, Angus Norton explains how market sizing rooted in real customer behavior, segmentation, and bottom-up logic leads to better GTM strategies and more credible growth plans. If you’ve ever been tempted to say “we just need 1%,” read this first.
If you've been involved with startups, venture decks, or GTM strategy sessions long enough, you've seen it: the oversized TAM slide. A bold number, often in the tens of billions, meant to impress investors or rally internal teams. It's usually followed by a hopeful line about capturing "just 1%" of that enormous market. On paper, that results in significant revenue. In reality, it's mostly noise.
TAM — or Total Addressable Market — has become one of the most overused and often misunderstood concepts in growth planning. While it has a place in strategic planning, it too usually clouds more than it clarifies. Especially when combined with vague "attach rate" assumptions, TAM slides can turn into little more than pitch theater. From my experience — across global platforms like Microsoft and high-growth SaaS companies like Xero — a more grounded, segmented approach to market sizing isn't just more accurate; it's essential for building scalable, focused businesses.
When I was at Microsoft, we thought about the market in terms of "sockets" — essentially, the total global PC installed base. According to IDC at the time, that number was around 1.5 billion units. That's a TAM by volume, not by value. Theoretically, each of those devices was a potential attachment point for Windows, Office, or one of our newer productivity or cloud services.
But we never treated that number as a single entity. We broke it down carefully — by device type, processor architecture, memory, graphics capability, OS version, geography, and channel. A PC running Windows XP in rural India wasn't the same opportunity as a new enterprise-grade laptop in Chicago. The differences in distribution models, customer needs, upgrade readiness, and product-market fit made each segment significantly different.
The more we refined the model, the closer we got to our Serviceable Addressable Market (SAM) — the portion of that 1.5 billion that we could actually serve, given our product fit and distribution reach. And even within that, we drilled further to define our Serviceable Obtainable Market (SOM) — the slice of customers we could realistically capture in a given year, considering our sales capacity, competition, and pricing.
Later, at Xero, the numbers were different, but the illusion of TAM was the same. On the surface, the market seemed limitless. The global small business population exceeded 200 million entities, with more than 30 million in the U.S. alone. That's a massive TAM for accounting software, right?
Not quite. We quickly learned that roughly 70% of small businesses still relied on spreadsheets, paper, or manual methods for their bookkeeping. They weren't in the market for a cloud accounting platform — at least, not yet. Which raised a fundamental question: was our real TAM only the 30% of businesses already using accounting software?
In truth, that 30% was closer to our initial SAM — the segment that was already aware of the category and ready to make a switch. But we didn't stop there. We looked at verticals, tech readiness, regulatory environments, and the role of bookkeepers and accountants in the buying decision. We mapped the ecosystem by behavior, not just headcount. The result was a bottom-up market model that told us where adoption would be fastest, stickiest, and most cost-effective.
That informed not just our market sizing, but our entire GTM strategy — from prioritizing geographies to shaping our partner program.
There's a close relative of TAM inflation that often appears in pitch decks: the attach rate shortcut. The common logic is usually something like this: "There are 10 million potential users, and if we can convert just 5%, that's 500,000 users. At $20 per month, that adds up to $120 million in annual revenue." This type of math might seem neat, but it's rarely accurate. Attach rates aren't random — they result from product-market fit, pricing strategies, user experience, competitive environment, and go-to-market execution. Assuming a uniform attach rate across a loosely defined user base is more wishful thinking than strategic planning. Even worse, it can cause teams to overbuild, overspend, or pursue segments that aren't yet ready to convert.
At Bodhi Venture Labs, we help clients build bottom-up models based on reality, not theater. That starts with defining your ideal customer profile (ICP) — not just by company size or sector, but by tech behavior, purchasing authority, pain points, and buying triggers. From there, we look at how many of those ICPs exist, how many you can reach with your current sales model, and how many are likely to convert based on actual data — not back-of-napkin assumptions.
We often layer in qualitative insights from customer discovery and early sales data to inform assumptions around conversion, usage, retention, and expansion. This results in more focused GTM plans, more defensible growth targets, and more effective fundraising narratives.
Because in the end, investors and boards don't want to be dazzled — they want to be convinced. The best way to do that isn't through inflated TAM slides. It's through credible, segmented, evidence-based planning.
TAM still has a role — especially in showing the ceiling. But strategy happens much lower: in the reachable market, in the real conversion paths, in the behavioral readiness of your buyers. That's where your focus should be.
So next time someone puts a $50B market size on a slide, don't ask, "How big could this be?" Ask instead, "Who exactly is ready to buy this today, and what do we know about how they buy?"
That's not just a better question — it's the foundation of a better business.
