BCG & Bain Case Math: Examples + 14-Day Plan

While BCG and Bain are distinct firms, their case interview math styles share similarities that differ from McKinsey's approach. Here's what to expect and how to prepare.

How BCG/Bain Math Differs from McKinsey

What this means: You'll often need to decide *what* to calculate, not just *how* to calculate it.

Common Question Patterns

1. Profitability Breakdowns

"The client's profit declined 20% last year. What could be the drivers, and how would you quantify them?"

You need to:

• Structure revenue vs. cost analysis
• Identify which levers to pull
• Calculate impact of each driver

2. Breakeven Decisions

"The client is considering a new product line. What would you need to know to determine if it's worthwhile?"

You need to:

• Identify required data points
• Set up the breakeven calculation
• Make assumptions where needed

3. Options Comparison

"We have three strategic options. How would you compare them financially?"

You need to:

• Define comparison criteria (ROI, payback, NPV)
• Calculate metrics for each
• Make a recommendation

Speed vs Structure Trade-off

BCG/Bain cases require balancing:

Structure: Taking time to set up the problem correctly

Speed: Not losing momentum with slow calculations

Best practice: Spend 15-20 seconds structuring your approach, then execute calculations efficiently.

14-Day BCG/Bain Math Plan

Week 1: Build Speed

Days 1-3: Mental Math Foundation

• Daily: 2 × Mental Math Sprints (start easy, progress to medium)
• Focus: Percentages, multiplication, division

Days 4-5: Business Calculations

• Daily: Case Math Drills (Profitability topic)
• Focus: Margin calculations, revenue breakdowns

Days 6-7: Integration

• Practice cases with math components
• Focus on structuring before calculating

Week 2: Add Complexity

Days 8-10: Multi-Step Problems

• Case Math Drills (Growth topic)
• Practice CAGR, compound growth
• Work on explaining your math

Days 11-12: Estimation

• Market sizing problems
• Practice making and stating assumptions
• Sanity check every answer

Days 13-14: Full Cases

• Complete 2-3 full practice cases
• Time yourself
• Review and address weak points

Example Questions & Solutions

Example 1: Profit Decline Analysis

"A retailer's profit dropped from $50M to $40M. Revenue stayed flat at $500M. What happened?"

Approach:

1. Profit margin dropped: 10% → 8%
2. Since revenue flat, costs increased
3. Cost increase: $10M on $500M revenue = 2% cost increase
4. Investigate: Was it COGS or SG&A?

Example 2: Investment Comparison

"Option A: Invest $10M, returns $3M/year for 5 years. Option B: Invest $15M, returns $4M/year for 6 years."

Calculations:

• Option A: Total return $15M, Profit $5M, ROI 50% over 5 years = 10%/year
• Option B: Total return $24M, Profit $9M, ROI 60% over 6 years = 10%/year
• Option A payback: 3.3 years | Option B payback: 3.75 years

Recommendation: Similar annual ROI, but A has shorter payback (lower risk). Choose A unless scale matters.

How to Use Case Math Drills for BCG/Bain

Recommended focus areas:

1. Profitability & Margins — Core to most cases
2. Growth & CAGR — Common in market entry cases
3. ROI & Payback — Investment decisions

Practice mode: Set topic filter, work through 10 questions, review explanations.

Key Takeaways

1. BCG/Bain expect you to structure the math problem
2. Open-ended questions require you to define the approach
3. Balance speed with accuracy
4. Practice explaining your reasoning
5. Estimation skills are important

Build your skills: Start Case Math Drills →