Case Interview Math: Complete 2025 Guide

Case interview math is one of the most critical skills you'll need to succeed in consulting interviews at McKinsey, BCG, Bain, and other top firms. This comprehensive guide covers everything you need to know.

Why Case Math Matters

In almost every case interview, you'll encounter numerical analysis. Whether it's calculating market size, determining profitability, or evaluating an investment, you need to be fast, accurate, and confident with numbers.

Core Formulas You Must Know

Profitability

• Profit = Revenue - Costs
• Revenue = Price × Quantity
• Gross Margin = (Revenue - COGS) / Revenue × 100%
• Operating Margin = Operating Income / Revenue × 100%

Breakeven Analysis

• Breakeven Units = Fixed Costs / (Price - Variable Cost per Unit)
• Breakeven Revenue = Fixed Costs / Contribution Margin %
• Contribution Margin = Price - Variable Cost per Unit

Growth & CAGR

• Growth Rate = (New Value - Old Value) / Old Value × 100%
• CAGR ≈ (End Value / Start Value)^(1/n) - 1
• Rule of 72: Years to double ≈ 72 / growth rate

ROI & Payback

• ROI = (Gain - Cost) / Cost × 100%
• Payback Period = Investment / Annual Cash Flow

Mental Math Tips

1. Round strategically: 47 × 23 ≈ 50 × 23 = 1,150
2. Break down complex calculations: 15% of 80 = 10% + 5% = 8 + 4 = 12
3. Use benchmarks: Know that 1/3 ≈ 33%, 1/6 ≈ 17%, 1/8 ≈ 12.5%
4. Practice daily: Speed comes from consistent practice

Practice Now

Ready to put these concepts into practice?

• Mental Math Sprint → - Build raw calculation speed
• Case Math Drills → - Practice business scenarios
• Brain Teasers → - Sharpen logical thinking

Next Steps

1. Bookmark this guide for reference
2. Start with the 14-Day Foundation curriculum
3. Practice 15-30 minutes daily
4. Track your progress with a free account

Ready for the next step? Check your consulting CV →

Considering finance roles too? The math skills here transfer directly. For IB/PE-specific prep, see Finance Interview Prep.