Advice on business sense and guesstimates

indeed - even if your structure is solid, weak numbers can hurt a guesstimate. 

good news is that it's just a muscle you can train;

estimations

• keep simple benchmarks in your head: e.g., a small city ~1m people, average coffee spend ~$10/week, revenue per store ~$1m/year
• round numbers to make math easier (47,300 → 50,000)
• sanity-check your final number. e.g., 2m cups/week for 1m people? probably off.
• practice different types of guesstimates. since you have a biochemistry background, try healthcare/science ones: “how many vaccines needed per year?” or “how many lab tests in a hospital per day?”

business sense

• read short articles or reports: McKinsey Insights on consumer goods, BCG Perspectives on healthcare, FT summaries
• pay attention to key metrics: growth, revenue, margins. e.g., startup with $1m revenue and $0.5m costs → 50% margin—does it make sense?
• think like a scientist: form hypotheses, test assumptions, draw conclusions
• practice cases with a peer or coach. e.g., “should this pharma company launch a new drug?” estimate market size, pricing, competition

small daily exercises and a few focused cases go a long way to strengthen both your estimation and business intuition.

If your structure is good but your estimates are off, you just need better starting points to work from. This is something you can build. And your biochemistry background isn't the problem you think it is.

Here's what helps with estimation:

You need a few key numbers in your head. Population of your country and big cities. Average household size. What people earn. What things cost: coffee, rent, a car, a flight.

When you know these, you can build estimates from something real instead of guessing.

Here's how I'd practice:

Spend 10 minutes a day for two weeks. Look up a number, memorize it, then use it in a quick estimate.

Example: How many coffees are sold in London daily? Start with population, filter to adults, then coffee drinkers, then how often they buy. Check your answer against real data. The gap shows where your thinking was off.

On building business sense:

Read The Economist or Financial Times for 15 minutes a day. Don't memorize. Just absorb how businesses talk about growth, costs, and competition. After a few weeks, it starts to click.

One more thing, your biochemistry background helps:

You already think in systems and variables. Business is the same: inputs, outputs, and trade-offs. Use that.

That feeling is entirely understandable. It's frustrating when you nail the structure, which is the hardest part, but get dinged on the numbers. The key distinction here is that while the interviewer is testing your logic, they are also testing your judgment about the real world.

When we talk about "weak estimations," it usually means your assumptions were unanchored, not that your math was flawed. The interviewer doesn't care if the final number is $10M or $12M. They care if you assumed 50% market penetration for a niche product in year one, or that the average American household has 10 people. The fastest fix is to create a personal fact base of anchor numbers. Memorize five things: the US population, the number of households, the rough split of the US GDP by sector (services, manufacturing), the rough margins for major industries (tech vs. retail), and standard growth rates (what is "good" growth vs. "hyper-growth"). Use these to benchmark every assumption you make in a guesstimate.

As for boosting your business sense coming from biochemistry, think of it as quickly learning a new language: the language of the P&L. You don't need an MBA right now. You need exposure to metrics. Every day, spend 30 minutes reading the Financial Times or The Economist. Crucially, don't just read the stories; pay attention to the quantification: What are the market sizes, what are companies paying for customer acquisition (CAC), and what are typical annual growth rates (CAGR)? This structured immersion will quickly give you the intuition needed to make grounded, reasonable assumptions, which is exactly what interviewers define as "business sense."

All the best on your next round!

Hi there,

To improve at guesstimates, it helps to practice with a small number of classic examples that build intuition. For instance, you could regularly estimate how many cups of coffee are sold in a city per day or how many smartphones are sold in a country each year. These types of questions train you to think in terms of population, usage, and frequency.

It’s also useful to practice an operational estimate, such as how many packages a delivery driver can realistically deliver in a day. This helps you get comfortable breaking capacity and time into simple, defensible assumptions.

When practicing, the goal isn’t to hit the “right” number but to use reasonable anchors, round numbers, and clean math. Always sanity-check the result by asking whether it feels too large or too small for the context. Over time, this repetition is what builds business intuition.

If helpful, I’m happy to suggest a short daily guesstimate routine to help you build speed and confidence quickly.

Best,
Evelina

hey! 

I would recommend the following to improve guesstimates and business sense:

• For guesstimates: always structure first (clear buckets), state assumptions out loud, use simple round numbers, and do a quick “does this feel too big/small?” check at the end.

• Practice 1–2 guesstimate questions daily (market size, number of customers, revenue) and review where your assumptions were unrealistic.

• For business sense: start reading short summaries of business news in sectors you know (biotech, pharma), and for each story ask: Who is the customer? How do they make money? What risks are they managing?

• Use your biochemistry background by focusing on questions like “How does this science save time, reduce risk, or make money for someone?” and train yourself to phrase answers in those terms rather than technical detail.

Let me know if you have questions!

Best, Alessa 

Hi there,

It will be hard to give sound advice without more details on why you think your estimates were weak. Otherwise, good northern star is to ask yourself whether you'd be able to reasonably defend the number that you're assuming.

That's a great question.

Exercise is an obvious one. Just practise more. Get feedback. Read the answers in whatever book you're practising with. You will steadily get better. At least until a certain point.

Another thing to do is to get expert feedback. Based on how you're describing it, your technique for generating assumptions is leading you down the wrong path. I doubt it's your lack of business knowledge, because unless they are interviewing you for a specialist role, they don't expect you to have any specific business knowledge. It's rather your approach to estimation that is problematic (e.g., not using a personal sample as a benchmark for the first assumption).

And yet another way of checking the assumptions is to flip them around (e.g., bottom-up to top-down).

If you want to work on this, drop me a line. 

Best,
Cristian

Some hypothesis:

- You are providing awkward assumptions. Either using random numbers, and not being able to justify why you are picking a certain number --> Please make sure your assumptions are grounded on something and validate them with the interviewer

- You are not considering the implications arising from your estimations. When you finish the estimation you have to ask two questions: 

1. Does this number make sense? I.e., is it the right order of magnitude? Do a quick check (e.g. compare to what would be the average spend per capita on the product)
2. How does this change the recommendation? Make sure you understand the implications of the number

Having said this - I have tens of drills for market estimates and regularly run sessions specifically customized for people who need to improve their market estimate skills. Feel free to reach out if you want to know more about it.