Every deck has a TAM slide. Most of them are wrong.

• Milind Soni
• April 29, 2026
• Blog
• #competewiser, #CompetitiveIntelligence, #MarketResearch, #MarketSizing, #Prodzen, #StartupStrategy, #StrategyConsulting, #TAM, #VentureCapital
• 0 Comments

Not wrong because the analyst is careless, wrong because TAM sizing is genuinely hard to do rigorously under time pressure.

Walk into any investor meeting or board review and you’ll find a market sizing slide. The number looks authoritative, backed by a named research firm, expressed to three significant figures, sometimes accompanied by a satisfying upward-sloping chart. And yet, more often than not, the methodology behind it wouldn’t survive thirty seconds of scrutiny.

That’s not a criticism of the analysts who built those decks. TAM sizing is genuinely difficult to do well under the time pressure most teams are working under. The mistakes that recur aren’t careless ones, they’re structural, baked into how the work gets done.

Here are the four patterns that show up most often.

Mistake 01: Using one approach instead of triangulating

A top-down number from a market report and a bottom-up build from unit economics should arrive at roughly the same place. When they don’t, that gap is the most important data point in the entire analysis, and most decks ignore it entirely. Triangulation isn’t just a validation step; it’s where the real insight lives.

Mistake 02: Accepting published figures without checking the base year

A “2024 market size” sourced from a 2022 report with CAGR applied forward is not the same as verified 2024 data. The distinction matters. They often get treated identically in decks, which means the downstream projections are built on a foundation that was never quite what it claimed to be.

Mistake 03: Confusing TAM with SAM

Total addressable market is not what your client can actually capture. Conflating the two inflates the apparent opportunity and sophisticated buyers notice immediately. The distinction between what the market is worth in aggregate and what’s realistically within reach is not a footnote; it’s the whole point.

Mistake 04: No stated methodology

A number without a methodology is just a number. Research that holds up under scrutiny, in an investor meeting, a board review, a competitive brief, is research where you can show your working. If the methodology isn’t documented, the number can’t be defended, updated, or trusted.

The fix isn’t complicated in principle, even if it’s demanding in practice. Rigorous TAM work needs a top-down data layer anchored to a verified base year, a CAGR-informed projection with stated assumptions, a bottom-up build from unit economics wherever possible, explicit triangulation between the two approaches, and a documented methodology that could survive an adversarial read.

What good TAM work requires 

• A top-down data layer from verified, dated sources
• A CAGR-anchored projection with stated assumptions
• A bottom-up build from unit economics where possible
• Explicit triangulation between both approaches
• A documented methodology that shows the working

When the top-down and bottom-up numbers align, that’s a signal your sizing is credible. When they diverge, that divergence deserves an explanation not a workaround. The gap between approaches is often where the most interesting strategic insight is hiding.

TAM sizing is one of the workflow agents inside CompeteWiser.

We’re opening trial access for research teams who want to run it on a live market, not a demo, your actual brief. There’s a short onboarding call to start. Drop a comment or send a message if you’d like to try it.