TAM SAM SOM: Worked Examples and What Investors Test

The TAM SAM SOM model is three nested market sizes. TAM (total addressable market) is the revenue if every possible buyer bought; SAM (serviceable addressable market) is the part your product, price and channels can serve; SOM (serviceable obtainable market) is the share of SAM you can win in the plan period.

The worked example runs from a real count of UK companies down to the revenue a CEO or CFO has to defend in front of an investor; a marketplace, where supply caps the SOM, follows for contrast.

Investors rarely stop at the TAM. The arguments start at the two steps below it: the filters that turn TAM into SAM, and the sales plan that turns SAM into SOM, the revenue the round is paying for.

How to calculate TAM SAM SOM: what each layer measures

Each layer in the TAM SAM SOM definition above is one multiplication. The table puts TAM vs SAM vs SOM side by side: the question each one answers, its formula and the input an analyst will ask you to source.

5 columns. Drag the table sideways; the first column stays put.

Use the table as a TAM SAM SOM template. Each layer and its figure go on the slide; the formula and the sourced inputs go in the appendix an analyst asks for after the meeting. The last column is your own list to check before the deck goes out.

spectup's pitch deck service sizes the market bottom up from real customers and prices before a single slide is designed: a number that can't be rebuilt from its inputs doesn't go on a page an investment committee will read.

TAM vs SAM vs SOM, worked on one UK software company

Illustrative example. A UK company sells workflow software to medium-sized businesses at GBP 20,000 a year per customer.

At the start of 2025 the UK had 38,435 medium-sized private-sector businesses, firms with 50 to 249 employees, according to GOV.UK's business population estimates. At GBP 20,000 each, that's a TAM of GBP 768.7M.

Assume two filters, each with its own source: 80% of those firms sit inside the sales team's reach, from its territory map, and half of those run the systems the product integrates with, from the integration partners' published customer counts. That leaves 15,374 firms, 40% of the count, and a SAM of GBP 307.5M.

The round funds a sales team that can sign 600 customers by year five, so SOM is 600 x GBP 20,000, or GBP 12.0M: 3.9% of SAM.

3 columns. Drag the table sideways; the first column stays put.

Here SAM is 40% of TAM, and every point of that 40% needs a reason an investor can check. The filters remove GBP 461.2M, more than half the market, and that SAM vs TAM cut is what an investor questions first.

In this TAM SAM SOM example the count is real; the price, the filters and the sales capacity are assumptions the company has to defend.

How do you calculate TAM top-down and bottom-up, and which figure do you carry?

Two methods give two numbers, and they seldom match; the gap shows which assumption carries the size of the market.

Top-down sizing starts from a published total and cuts it down by country, sector and company size. For a European market, a top-down build can start from Eurostat's structural business statistics: 34 million enterprises were active in the EU business economy in 2024, and 5.4 million of them worked in professional, scientific and technical activities.

Bottom-up market sizing counts the buyers and multiplies by a price you can evidence, as the worked example did with 38,435 firms.

• Top-down is fast and carries a third party's name, and it inherits every definition the report used, including segments you don't sell to.

• Bottom-up takes longer, rests on a count and a price you can show, and is the version an investor can rebuild in a spreadsheet.

• Reconciled puts both side by side and explains the gap line by line.

In this video from my channel I go through why a giant top-down TAM no longer convinces investors, and what they check on a market slide.

Illustrative example: a marketplace, sized from the Eurostat count. A marketplace matches EU professional-services firms with freelance specialists and keeps EUR 1,500 a year in fees from each firm that hires through it. Eurostat's 5.4 million firms in those activities give a TAM of 5.4 million x EUR 1,500, or EUR 8.1bn.

Assume two filters: 40% of those firms sit in the three countries the marketplace operates in, a share a real build would read from Eurostat's figures by country, and 60% of them already buy freelance work, from the company's own survey. That leaves 1,296,000 firms and a SAM of EUR 1.94bn, so SAM is 24% of TAM.

In a marketplace the SOM is capped by supply. If the round funds 1,500 vetted specialists by year five, each serving 8 firms a year, SOM is 12,000 firms x EUR 1,500, or EUR 18.0M: 0.9% of SAM, and the investor's first question is where the 1,500 specialists come from.

Illustrative example, back to the UK company. Two paid market reports size its market at GBP 1.0bn to 1.4bn and GBP 1.2bn to 1.7bn. The bottom-up count, priced anywhere between GBP 15,000 and GBP 25,000 a year, gives GBP 577M to GBP 961M.

spectup's rule on the decks it builds is to reconcile two licensed sources against each other, carry the lower figure and name the source it came from.

In the UK example the lower-figure rule lands on the bottom-up count: GBP 768.7M at the GBP 20,000 the signed contracts show, lower than either report. The GBP 15,000 to 25,000 band is the price sensitivity, not a second estimate.

Report A's GBP 1.0bn, the lower of the two reports, sits beside it on the slide as the named cross-check, and the gap is explained by what the reports count and the bottom-up leaves out, such as larger firms or adjacent software categories.

How do investors test the numbers at each round?

The test changes with the round, because each stage has different evidence to check the market against. A Series A investor has a count and a plan to look at; a growth investor has three years of revenue and a budget for outside diligence.

Series A. Is the SAM vs TAM cut made by filters the company states, and is the bottom-up count real? The investor rebuilds the 38,435 x GBP 20,000 line and asks where the 40% comes from.

Series B. Does SOM reconcile with what's already on the books: ARR, pipeline, win rates and cohort retention? A plan for 600 customers needs a win rate and a sales cycle that two years of data already show.

The Series B test ends on two numbers: how big the SAM is, and how much of it the plan needs. Shrink the SAM to GBP 60M and the same GBP 12.0M plan needs 20% of it. A GBP 40M plan on the GBP 307.5M SAM needs 13.0%, and skipping the filters, with the whole GBP 768.7M TAM used as the SAM, makes the plan look like 1.6%.

Growth and private equity. Commercial due diligence, an outside study of the market that the investor pays for, checks the numbers independently. In one Strategy& case for a private equity investor, the team assessed market size and penetration rates in key geographies and determined five-year growth rates.

The market slide is rarely the slide that decides a round. In the NBER survey of 885 venture capitalists, investors rated the management team as more important than business characteristics such as the product or the technology.

A weak market slide still costs the team: the arithmetic is theirs, and the market build sits in the data room for investor due diligence next to the model.

Which TAM SAM SOM mistakes do investors catch first?

A 2025 BCG benchmark of more than 100 private software companies notes that companies moving into adjacent categories are "also looking for a large TAM to highlight to prospective investors", and argues they should first understand their ideal customer profile and the true TAM that results.

Five mistakes an analyst can catch from the deck and its sources:

1. A TAM that counts buyers the product can't serve. The investor asks which of the counted firms have bought, and the answer covers one segment of the count.

2. One source, no date. The analyst opens the report and finds a different year, a different currency or a different definition of the market.

3. A SOM written as 1% of a huge market. A share picked off the top of the market names no customers and no hires, and an analyst asks for both.

4. A SOM bigger than the sales capacity the round pays for. The check is customers per account executive per year, times the hires in the use of proceeds, the sum the worked example runs in the next chapter.

5. A market slide that disagrees with the model. ARR at the end of year five in the model against SOM on the slide: two numbers mean one of them is wrong.

Mistake 5 is settled at the pitch deck outline stage: plan the market slide and the financials slide around one SOM before either is drawn.

Why the market slide and the financial model must show the same SOM

SOM is a revenue line the round pays for: the money hires the sales team, and the customers that team signs are the SOM.

Illustrative example. In the worked example, the round funds a team that signs 40 customers in year one, 70 in year two, 120 in year three, 170 in year four and 200 in year five. With no churn assumed, that's 600 customers and GBP 12.0M of ARR by the end of year five, 3.9% of SAM.

Three account executives already sell, and the use of proceeds hires 2, 4, 6, 4 and 2 more at the start of years one to five. Each signs 10 customers a year at full ramp and 5 in the year they join, after a six-month ramp: year one is 3 x 10 + 2 x 5 = 40, year five 19 x 10 + 2 x 5 = 200.

The same five numbers belong on the pitch deck financials slide and in the revenue tab of the model, and the use of proceeds has to show the hires that sign them. If the model shows GBP 15M of ARR at the end of year five and the slide shows GBP 12.0M, the analyst rebuilds the hires from the use of proceeds to find out which one holds.

How spectup builds a TAM SAM SOM pitch deck slide

spectup works for the company raising the round; the investor is the reader the slide has to convince. Market research is the third step of the deck work, after strategy and story and before design, and our consultants run it.

The market size is built in four layers, each sourced on its own and each a line on the slide:

1. Total market where the company sells, the TAM, from two licensed sizing databases reconciled against each other and against the bottom-up count, with the lower figure carried and named.

2. The segment that can buy, the SAM, from filings and registry counts.

3. What's reachable inside the plan period, the SOM, from the company's own coverage and sales capacity.

4. What's held today, the revenue already under contract, from the signed contracts.

Anything we can't stand up twice is cut. The same research covers the competitive map, with doing nothing plotted as an alternative, and the macro context, with a source behind every number.

The research is covered by the engagement and priced into the pitch deck cost. After delivery, spectup can take the deck to investors as well, on a record of $760M+ advised, raised or placed.

Choose the SOM you can defend before you choose the TAM

Build the TAM SAM SOM slide in reverse. Start with SOM: the hires the round pays for, the customers they can sign each year, the price in your signed contracts.

Size SAM next, from a dated count, and write down every filter with its source. Let the TAM be whatever the sources say, even when it's smaller than the number you hoped to show.

Then put the slide through the six checks an analyst makes before writing the investment memo a committee reads:

• Is the count under your TAM sourced and dated, the way 38,435 is from GOV.UK?

• Is every filter between TAM and SAM written down, with a source an analyst can open?

• Did you run top-down and bottom-up, and can you explain the gap between them?

• Does the slide carry the lower figure and name where it came from?

• Does SOM equal the model's ARR at the end of year five, customer for customer?

• Could an analyst rebuild every number from your appendix without calling you?

GBP 12.0M is 3.9% of a SAM an analyst can rebuild. As 1.6% of an unfiltered TAM it would not survive the first call.