Best Practice Approach for Case Interview Math + Tips and Examples


Our best practice approach for case interview math will help you show that you can make precise calculations when required while finding shortcuts when you’re short on time. Since consulting is all about fact-based problem solving, you need to show that you are strong at quant. The most straightforward way to assess your quant skills is through your calculations during the case interview. During the case interview, the interviewer assesses your ability to make accurate calculations and your ability to make practical estimations. 


Best Practice Approach: Case Interview Math

As mentioned above, two types of math skills are assessed in a case problem: precision and estimations. 

Unless the interviewer explicitly asks otherwise, you can assume that you are required to make a precise calculation. However, if the numbers seem challenging, you can ask if it’s okay to proceed with an estimation. If your interviewer confirms it, you can round the numbers by +/- 5%. 


Helpful Tips: Case Interview Math


Use abbreviations for high numbers. For instance, M (or 106) for million and B (or 109) for billion. That’s how you can simplify the numbers and make the calculations easier to follow. 



If you’re on a video interview, the interviewer will not be able to see your calculations. Take advantage of that situation by cross-checking your numbers on paper, not via a calculator which is not allowed, before telling the interviewer. Most candidates rush to say the solutions, but it pushes them to make mistakes.


Keep track chronologically

Make your calculations on the same sheet as the case solutions. This helps you to keep track of your solutions chronologically. 


Case Interview Math: Best Practice Examples 

Below, you can find two different examples demonstrating precision and estimation problems.


For precise math, suppose that you are given information about the battery market size in the world and asked to do an accurate calculation. The data is composed of the following:

1. World population: 7.9B

2. Proportion of people in need of devices with portable batteries: 40%

3. Number of portable batteries annually demanded per eligible person: 0.15

  • Total=$7,900M*40%*0.15
  • =$3,160M*0.15
  • =$474M


If you’re allowed to round the figures, you can do the following: 

  • Total=$8B*40%*0.15=$320M*0.15=$480M
  • As you can see, the results are almost the same, and it takes much shorter to estimate. 


Case Interview Math: How to practice

You can use Prepmatter materials to practice all aspects of case interview math. First, you can use our free math drills to brush up on your math skills and financial acumen. Our Get the Offer Course includes 100 quantitative questions, 50 exhibit drills, 10 detailed market sizing questions, and 40+ cases, which are heavily quantitative. In addition, our online assessment package includes four numerical assessment tests, each with 23 questions. 


Looking for more practice opportunities?

We recommend utilizing online resources to practice mental math questions. You can also ask your Prepmatter coach to train you specifically on math precision and estimation. 


Remember, case interview math is a critical part of consulting. Using our tips and resources will help you succeed in showing accurate calculations and practical estimations.