Every pitch deck has a TAM slide, and most of them are doing more harm than good. A big total addressable market number impresses nobody who has seen 200 decks, and it pushes the team behind it to sell to everyone, which is the slowest way to sell to anyone. The number that decides whether a startup grows is the SOM, the market you can win in the next 12 to 24 months. Getting there means knowing what each of the three numbers measures and where founders go wrong with them.
TAM counts everyone who could buy, which is why it's useless on its own
Total addressable market is the revenue you'd make if every possible customer bought from you and nobody else. It's a theoretical ceiling, and it's the number most likely to get rounded up before an investor meeting.
Here's what a typical TAM claim sounds like: "18 million businesses could use our product."
Here's what it leaves out: how many of those 18 million have the problem you solve badly enough to pay for a fix this year. Usually that's a small fraction, and the deck doesn't say which fraction. Knowing the market is large only helps if you can reach some of it, and a 12-person startup can't reach 18 million of anything.
TAM is a starting point for market sizing and nothing more. The trouble starts when a founder treats it as the plan.
SAM narrows it to who you can serve, and it's usually still too wide
Serviceable addressable market is the slice of TAM your current product, sales channels, and team can serve. That's a real improvement over TAM. It's also where most startups stop, and the SAM they land on is something like "all companies with 1,000 employees."
That's still too many kinds of buyer. A 1,000-person law firm and a 1,000-person logistics company have different decision-makers, different budgets, and different reasons to buy, and a small team can't run a sales motion that fits both. April Dunford's positioning process puts a whole step on this, which she calls determining who cares a lot: the customers who get the most value from what makes you different. Two questions get you there. Who feels this pain worst? And where can you deliver something the alternatives can't?
Answer those and your SAM stops being a headcount filter and starts being a group of people with a shared problem.
SOM is the market you can win, so it's the number that matters
Serviceable obtainable market is the part of SAM you can realistically take in a set window, say the next 12 to 24 months, with the team and budget you have. It's the smallest of the three numbers and the only one that tells you what to do on Monday.
A useful SOM sits where three things overlap. The customers can pay and want to. You can reach them with the sales and marketing you have now, without a channel you'd need to build first. And there's something about your product they'd pick you for over the current option. Miss any one of those and you're describing a market you'd like to have, which is the TAM problem again in a smaller font.
Geoffrey Moore's word for this segment in Crossing the Chasm is the beachhead, and his instruction is blunt: "Concentrate an overwhelmingly superior force on a highly focused target." The point of the beachhead is that winning it gets you the references, the case studies, and the word of mouth that make the next segment cheaper to win. Moore again: "if we don't take Normandy, we don't have to worry about how we're going to take Paris."
Related: The Essential Guide to Why, When, and How to Niche Down
Founders inflate TAM because narrowing feels like giving something up
Most founders know all this and still put the 18 million on the slide. The reason is usually fear, and it sounds like this: "If we say we're only for medical practices, investors will think the market's too small and customers outside that group won't call."
Both worries are backwards. Investors who've done this before know that a startup owning a segment is worth more than a startup nibbling at a category, and the customers outside your segment weren't going to close anyway. They were going to take three demos, ask for a feature you don't have, and go with the market leader. The wider the target, the longer the sales cycle, the steeper the discount at the end of it, and the more runway spent finding out which buyers were real.
The failure data backs this up. CB Insights' 2026 post-mortem of 385 failed VC-backed startups found that 43% died of poor product-market fit, and two-thirds of those were early-stage companies that never found a market at all. A big TAM is a good way to never find one.
Specific positioning makes the SOM real
Once you've picked the segment, the homepage and the pitch have to say so. Compare two ways of describing the same product.
"A scheduling platform for SMBs."
"Scheduling for medical practices with 10 to 50 employees that are losing patients to no-shows."
The second one tells a practice manager in one sentence that you know her problem, and it tells everyone else to move on, which is the point. Same for the enterprise version: "cloud cost management for enterprise IT" says nothing, and "cloud cost control for DevOps teams in financial services that just got a surprise AWS bill" says everything. Narrow positioning is what turns a SOM from a number in a spreadsheet into a group of people who recognize themselves on your website.
How to size the market you can actually win
Five steps, in order. Skipping ahead is how you end up back at the TAM slide.
- Start from the problem. List who has it worst, how often, and what it costs them. Demand comes from the problem, so that's where the market sizing starts.
- Talk to 20 of them before you scale anything. Pilots and customer calls tell you whether the pain is as sharp and as common as the deck claims. Often it's sharp in one sub-group and mild everywhere else, and that sub-group is your SOM.
- Turn down the customers who don't fit. Every off-target deal costs support time, roadmap space, and a reference you can't use.
- Rewrite the positioning for that segment. Say who it's for and what it fixes in the first sentence of the homepage.
- Plan the second segment, then wait. Win the first one. Get the case studies. Move when the references from segment one are opening doors in segment two on their own.
Related: A Growth Hacker's Guide to Reducing Customer Churn
What to put on the TAM slide instead
Keep the TAM slide. Put the big number on it, then put the SOM right under it, with the segment named and the reason you'll win it. "About 4,000 medical practices with 10 to 50 employees, 60% of which still schedule by phone, and we're the only option that plugs into their existing EHR" beats "18 million businesses" every time, because it tells the reader you know how you're going to get the first 40.
The size of the market has never been the thing that decides whether a startup wins it. The next time you're building the slide, spend the time on the small number.
Subscribe to receive the latest blog posts to your inbox every week.
.jpg)
