What's the best approach to getting ready for Market sizing questions at EY financial services consulting ?

Hi Solene,

For EY Financial Services, market sizing is less about clever tricks and more about clear structure, realistic assumptions, and business logic. Here’s how to prepare effectively for the final round.

Best approach to market sizing

• Always start with a simple top-down structure and say it out loud before calculating
• Use a standard formula such as
  market size = number of customers × usage frequency × price
• In financial services, anchor your assumptions in real-world behavior (e.g. number of bank accounts per person, average transaction values, penetration rates)

What EY specifically looks for

• Clean, logical structuring before math
• Reasonable assumptions that you can justify
• Comfort with ambiguity rather than perfect precision
• Clear synthesis at the end (“This implies a market of roughly X, which is attractive / small / risky because…”)

How to practice in the days before

• Redo classic FS market sizings (retail banking products, insurance policies, payments, lending)
• Practice talking through the math calmly under time pressure
• Focus on rounding, order-of-magnitude accuracy, and keeping numbers simple
• Always close with a business takeaway, not just a number

If you want, I can help you practice FS-specific market sizings and pressure-test your structure.

Best,

Evelina

That feedback is a huge win—it tells you exactly where the gaps are, which is rare this late in the game. You should treat that specific instruction on market sizing and structuring as your final exam syllabus.

For market sizing, the goal in the final round is not mathematical accuracy; it is the transparency and logic of your assumptions. Practice stating your initial assumptions clearly (e.g., population segmentation, usage rates) before you start calculating. For EY FS, make sure your practice cases use relevant metrics: measuring the market size for blockchain adoption among mid-tier banks, estimating AUM migration post-merger, or calculating the annual spend on regulatory compliance software. Use simple, round numbers so you can perform the math confidently without a calculator.

The "structuring" feedback is usually the more significant hurdle. It means the interviewer wants to see you take ownership of the problem and lead the solution, rather than just waiting for prompts. When you get the case prompt, your immediate goal should be to quickly build a framework (MECE is paramount) and verbally check the framework with the interviewer. Do not just present a list of buckets; explain why those buckets are important and how they flow together to answer the client’s core question. This demonstrates executive presence and logical command.

You’ve clearly demonstrated the raw analytical horsepower to get through four cases already. Focus your final prep time entirely on practicing these components out loud with a partner—specifically the introduction, structuring, and assumption-setting phases of the case.

All the best in the final round!

First of all, it’s great that you received specific feedback, that’s very actionable and absolutely fixable with focused practice.

For market sizing at EY FS, I’d focus on the following:

• Practice market sizings regularly and memorize a few key reference points (e.g., population sizes, GDP per capita). These anchors help you calibrate assumptions, do quick sanity checks, and feel more confident under pressure.
• Be comfortable with both approaches:
  Top-down and bottom-up. In interviews, top-down is often faster and cleaner, but knowing both allows you to adapt and shows flexibility. Practice until switching between them feels natural.
• Always lead with logic before math. Clearly explain your structure and assumptions before calculating. This communication piece is essential and often underestimated. Interviewers want to follow your thinking, not just see a number.
• Remember: it’s not about getting the “right” number. It’s about making reasonable, defensible assumptions and simplifying a complex problem in a structured way.

What really helps build confidence is integrating market sizing into everyday life:
for example, estimating how many patients a doctor sees per day/month while you're waiting in the waiting room. This trains structured thinking beyond formal case practice.

For business case structuring, targeted practice is key. Focus specifically on building clear, MECE frameworks and articulating why your structure answers the question, not just listing buckets or memorizing frameworks.

Overall, the feedback you received is a strong signal: it tells you exactly where to focus, and with a bit of deliberate practice, this is very doable. If you want to practice market sizing or structuring together, feel free to reach out.

Hope this helps!

Hi Solene, 

some thoughts around your question below (good luck for the final interview!!).

Market Sizing

• Understand top-down and bottom-up (supply vs. demand): Size the market using the approach for which you have the most general knowledge or best assumptions, or apply both to triangulate the market size from two perspectives 

  • Simplified exemplary top-down logic: Total population × penetration rate × average price

  • Simplified exemplary bottom-up logic: # of players × average customers per player × average price

• Decompose the drivers ("peeling the onion"): Break the market into its key levers and underlying drivers to demonstrate business acumen (e.g., further segment customers or tier market players)

• Sanity check the results (reality check): Validate your estimates by comparing them against proxy benchmarks to ensure they pass the “smell test” (e.g., cross-reference your calculated total market value with the size of a representative player in the market you might know and derive the implied market share)

Business Case

• Establish the financial core: Build a simplified paper model covering revenue, operating costs, and implied profit over the time horizon, while accounting for one-off investments (CAPEX) – Include relevant KPIs such as break-even point, return on investment, profit margins etc.

• Think in scenarios (sensitivity analysis): Always think in scenarios (base, bull, bear case) and clearly articulate which assumptions change, along with the resulting sensitivities and implications (e.g., a recession leads to lower-than-expected transaction volume, reducing ROI by X%)

• Craft the narrative ("the movie"): Don’t just adjust numbers; tell the strategic story behind each scenario (e.g., in the launch phase, we offer a “Zero Fee” promotion. This results in initial losses but accelerates customer acquisition. The “movie” is that we are building a large user base early to cross-sell other profitable products later

Get practical as much as possible (solo or with peers from PrepLounge) or learn from consultants by watching mock case interviews (I personally found "Management Consulted" on YouTube very helpful). Develop a rough understanding of market sizes, key players, and value drivers relevant for FS projects (e.g., insurance, banking). Online market research, annual reports, and casing books can serve as good first sources.