The founders end up building their market size slide the night before the pitch. They Google some industry report, copy the decent-looking number from it, decrease it by several percentages, multiply by another value, and voilà, there you have it- $20 billion. If we win just 1%, that's $200 million of market size. This approach is simple, intuitive, and, from the investor’s perspective, almost insulting.
TAM, SAM, and SOM give you three different perspectives on the same issue, the size of your market and, consequently, the value of your own share of it at a specific moment.
TAM, SAM, and SOM are three concentric market-sizing estimates that help businesses understand the true scale of their opportunity and communicate it credibly to investors. Getting these numbers right is one of the first things a pitch deck reviewer checks. Getting them wrong (usually too large or unsupported) is one of the fastest ways to lose credibility.
The reality is that market sizing is not an analytical exercise in which you try to find the largest receptive market compatible with your product. It is a discovery process where you determine your customer base, its approximate size, and the amount of resources needed to acquire that base.
A thorough market sizing analysis conducted properly will help you build a solid business plan for a significant amount of time even if your project is destined to fail in about a year inside the incubator.
What Are TAM, SAM, and SOM?
| Term | Full Name | Definition |
|---|---|---|
| TAM | Total Addressable Market | The total global or national revenue opportunity if you captured 100% of the market, the theoretical maximum |
| SAM | Serviceable Addressable Market | The portion of TAM your product/service can realistically target given your geography, language, business model, and capabilities |
| SOM | Serviceable Obtainable Market | The portion of SAM you can realistically capture in the near term (3 to 5 years) given your current resources, competition, and go-to-market |
Two Approaches to Calculating TAM
Top-Down Approach
Start with total industry data from research firms (IBISWorld, Statista, Gartner, McKinsey) and narrow down using your market share assumptions.
Example: Global CRM software market = $80B. You are building a CRM for independent insurance brokers in India. India represents ~3% of global SaaS spend = $2.4B. Insurance vertical = ~8% of all CRM use = $192M TAM.
Bottom-Up Approach
- Build from the customer level: number of potential customers × average revenue per customer.
- Example: 45,000 independent insurance brokers in India × $600/year average SaaS spend = $27M TAM. This is lower than the top-down figure, which is more credible because it is built from real unit economics.
The TAM mistake I see most often is a founder who can quote a market size to the dollar but can't say how many customers are in it. The number comes from an industry report, includes segments the product will never serve, and falls apart the first time someone asks what an average customer pays.
Investors don't spend much time on TAM. They go straight to the bottom-up math behind SOM: how many customers, at what price, acquired through which channels, at what cost. If those numbers hold up, the TAM slide rarely gets challenged.
Abhinav Gupta, CPA, CA, MBA · LinkedIn
Worked Example: TAM → SAM → SOM
Business: B2B accounting software for Indian e-commerce sellers
| Metric | Calculation | Amount |
|---|---|---|
| TAM | All Indian e-commerce sellers needing accounting software: 500,000 sellers × $300/year | $150M |
| SAM | Sellers with >$500K/year revenue (your product's fit): 80,000 × $300/year | $24M |
| SOM (Year 3) | Realistic capture with current team and budget: 2,000 customers × $300/year | $600K |
Investors know the TAM is theoretical. The SOM is what they probe. Be ready to defend how you get to 2,000 customers, CAC, channels, conversion rates, and sales cycle.
Common TAM Calculation Mistakes
- Claiming the entire market as TAM: 'The global accounting software market is $20B and we just need 1%', this is not a TAM calculation, it is a wish
- Using top-down only without a bottom-up cross-check: research firm numbers often include segments you cannot serve
- Confusing TAM with SAM: TAM is theoretical total; SAM is realistic target; presenting TAM as your target market inflates the opportunity
- No sources cited: all market size claims need a credible source, IBISWorld, government data, industry associations, or your own primary research
We came to Profitjets with a top-down TAM based on the size of the overall market, but it didn't explain how we would actually reach those customers. Profitjets rebuilt the model from the bottom up using our target customer segments, pricing, and realistic acquisition assumptions. The revised SOM was much more conservative, but it gave us a financial model we could defend in investor conversations and a clearer revenue path to plan around.
Book a free consultation and we will pressure-test the numbers.
FAQs
What is a good TAM for a startup?
It depends on how the business is funded. Venture investors generally look for markets large enough to support a very big company. For a bootstrapped or small business, a smaller, well-defined market is often better, because what matters is whether the SOM supports a profitable, sustainable business.
Which matters more to investors, TAM or SOM?
SOM, backed by a credible plan. Investors know TAM is theoretical. What they want to understand is how many customers you can win, through which channels, at what cost, and how quickly. A realistic SOM with clear math is more convincing than an impressive TAM with no path to it.
Should small businesses bother calculating TAM?
Yes, even without investors. Working through TAM, SAM, and SOM helps you set realistic sales targets, decide which customer segments to focus on, judge whether a new product or location is worth pursuing, and build a more grounded budget.
Where can I find data for market sizing?
For US businesses, useful starting points include government data such as the Census Bureau's business statistics, industry associations, trade publications, and paid research reports. Your own data, including customer interviews, sales conversations, and pricing tests, is often the most credible input for a bottom-up estimate.
How often should I update TAM, SAM, and SOM?
Revisit them at least once a year, and whenever you change pricing, add a product, enter a new region, or prepare to raise money. SOM should be updated most often, because it depends on your actual sales performance and budget.
Written by
Abhinav Gupta, CPA, CA, MBA
Abhinav works with business owners across the US on industry-specific bookkeeping, from dental practices and restaurants to construction and e-commerce. He writes about what each trade's books actually need. Connect on LinkedIn
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