If you’re preparing for case interviews, you’ve probably heard of “Consulting Math” – yes, consultants are known for doing fast mental math. But don’t panic, let’s talk about it. Consulting math isn’t about memorizing formulas or proving theorems; it’s about structured, logical problem-solving that helps businesses make decisions quickly.

Why Do Consulting Firms Care About Your Math Skills?

Because consultants work with numbers constantly – whether estimating market size, assessing investments, or projecting revenue. And since clients expect fast updates, being able to do quick, back-of-the-envelope calculations is a key skill. The goal isn’t to get a perfect number but a good enough one to guide decision-making.

Also, clients don’t just want numbers – they want clarity. If your math makes sense but your explanation sounds like a science 101 lecture, you’ll lose their attention. The key is to communicate your approach concisely and clearly so they nod along.

The 5-Step Approach to Ace the Math Question

We will introduce you a simple, structured approach to tackling any quantitative question in a case interview:

1. Understand the Question

Before diving into calculations, make sure you’re solving the right problem. Consultants don’t do unnecessary work (it’s bad for margins and your work-life balance).

• Recap: Summarize what you’ve understood. This buys you time to think and ensures you're aligned with the interviewer.
• Clarify: Ask smart questions about definitions, scope, and high-level assumptions (e.g., timeframe, units, or market segment).

Example:
Interviewer: "Estimate the annual revenue of a small coffee shop in New York."

You: "Just to clarify, are we looking at a single-location coffee shop or a chain location? And should I focus only on coffee sales, or include food and merchandise?"

2. Structure Your Approach

You wouldn’t assemble IKEA furniture without instructions (or maybe you would, but let’s be honest – it rarely ends well). The same applies here: create a framework before jumping into calculations

• Ask for time: "Do you mind if I take a minute to structure my approach?"
• Write it down: Break the problem into logical steps. A well-structured approach shows you think like a consultant.

Example Framework for Coffee Shop Revenue (Bottom-Up Approach):

1. Estimate the number of customers per day
2. Calculate the average spend per customer
3. Multiply by the number of operating days per year

You can also structure your framework using a top-down approach. This method starts with a broad number and progressively narrows it down on logical assumptions. For example, you might begin with the total population of New York and determine: How many people drink coffee? On average, how many cups does each person consume per year? By breaking the problem into these key components, you create a clear and structured path to your estimate.

3. Communicate Your Framework

Before crunching numbers, walk your interviewer through your thought process, including any assumptions you made along the way. It's also a great timing to ask your interviewer for any missing data to support your calculations. If they disagree, it’s better to adjust now rather than after a full calculation.

• Explain step by step: "I'll estimate the daily number of customers, factoring in variations between peak and off-peak hours. Next, I will determine the average spend per customer and finally extrapolate to a yearly figure. Does that approach make sense to you?"

4. Crunch the Numbers

Now it’s time to plug in numbers – but remember, you’re not being tested on your ability to be a human calculator. So keep it simple and make the mental math easy for yourself.

• Make reasonable assumptions.
• Break numbers down for easier calculations.

Example Calculation:

• Customers per day: 200
• Average spend per customer: $5
• Operating days per year: 350

You: “Assuming each coffee takes about 2 minutes to prepare on average, a barista can serve approximately 30 customers per hour during peak hours. If a coffee shop operates from 6 AM to 5 PM, we can estimate around 5 peak hours each day, resulting in 150 customers during peak times. For the remaining off-peak hours, let's assume the shop receives 1 customers every 10 minutes. With 6 off-peak hours in the day, that would add up to around 40 additional customers. Summing both peak and off-peak periods, the total estimated daily customer count would be 190. For simplicity, let's round this up to 200 customers per day. A cup of coffee on average is about $5 based on my experience and assuming the shop operates for 350 day per year (accounting for some holidays), the estimated annual revenue would be 200 × $5 × 350 which equals to $350,000"

5. Sanity Check and Insights

Even if your math is correct, always check if your answer makes sense and its implication to clients. Clients don’t want a consultant who estimates a single coffee shop makes $1 billion a year.

• Reality check: “Given that coffee shops typically have relatively low margins (around 10%), a small shop with one or two employees generating $350,000 in annual revenue seems reasonable”
• Sensitivity analysis: Identify key drivers – if the price per cup increased by 10%, how much would revenue change?
• Provide insights: "To increase revenue, the shop could introduce higher-margin products like pastries or loyalty programs to boost repeat customers."

Final Tips

Mastering math questions in case interviews is about structure, clarity, and confidence, not just speed. By following these five steps, you’ll show your interviewer that you think like a consultant, even if your mental math isn’t lightning-fast.

Now, grab a coffee and start practicing at MECE Academy.