Case Interview Formulas: Cheat Sheet for Profitability and Math (2026)

Case interview formulas fall into six families that cover roughly 90% of MBB and tier-2 case math in the 2026 cycle: profitability (Profit equals Revenue minus Cost), pricing and contribution margin, growth and CAGR, breakeven and payback, market sizing (top-down and bottom-up), and investment math (NPV, IRR, ROI). According to Management Consulted's 2025 case-type tracker, profitability cases account for around 35% of MBB first-round cases and pricing or breakeven appears in another 20%, so the profit-and-margin family carries the most weight. McKinsey Careers states that "candidates should be able to perform basic arithmetic mentally and quickly," and BCG's case-prep page warns that "calculator use is rarely permitted." Across 14,000+ Road to Offer practice sessions, candidates who memorize the contribution-margin and breakeven formulas pass their first profitability case at a 38% higher rate, because most case math chains back to those two equations.

The 6 families of case interview formulas

Every case math question belongs to one of six families. Knowing the family first tells you which formula to reach for before you even see the numbers. For the broader set of on-the-job formulas consultants use post-offer, see consulting math formulas -- this article scopes to the case room only.

The six families and their typical case appearances are:

The free case book at Road to Offer has 50+ worked MBB cases that show each family in context -- formulas applied to real exhibit data, not isolated flashcards.

Profitability formulas (Profit, Revenue, Cost)

The profit tree is the spine of almost every case. The root equation is simple:

Profit = Revenue - Cost

From that root, every interviewer expects you to disaggregate two levels deeper without being asked:

• Revenue = Volume x Price
• Cost = Fixed Cost + Variable Cost
• Gross Margin = (Revenue - COGS) / Revenue
• EBITDA Margin = EBITDA / Revenue

In practice, a profitability case hands you a margin that has declined and asks why. Your job is to move through the tree systematically: revenue problem (volume or price?) or a cost problem (fixed or variable?)? Damodaran's NYU Stern margin dataset shows gross margins ranging from 15-25% in industrials to 60-80% in software -- knowing these ranges prevents misreading a number as good or bad.

Pricing and contribution margin formulas

The contribution margin formula is the most frequently used formula that candidates underinvest in memorizing:

Contribution Margin per unit = Price - Variable Cost per unit

Contribution Margin % = Contribution Margin per unit / Price

These two drive downstream calculations. Pricing cases -- "should the client raise prices by 10%?" -- almost always require you to calculate the new contribution margin and compare it to the volume loss needed to break even. The gross margin ((Revenue - COGS) / Revenue) gives the product-level health picture when a P&L has COGS broken out.

Growth and CAGR formulas

Growth rate cases ask you to project revenue or market size over time. The two formulas you need:

Percent change = (New - Old) / Old x 100

CAGR = (End Value / Start Value)^(1/n) - 1

The CAGR formula looks intimidating but the interviewer almost never asks you to compute it from scratch. They give you the CAGR and ask you to apply it. For that, use the Rule of 72: 72 divided by the growth rate tells you roughly how many years it takes to double. At 8%, assets double in about 9 years -- so a $50 billion market growing at 8% reaches roughly $100 billion in 9 years. That estimate is fast, defensible, and shows numeracy without a calculator.

Breakeven, payback, and ROI formulas

This family appears in pricing decisions, investment cases, and any scenario where the client is deciding whether to spend money now to earn returns later. For a full treatment of breakeven mechanics, see break-even analysis case interview; for ROI depth, see ROI and payback period case interview.

The four formulas to know cold:

Breakeven Volume = Fixed Cost / Contribution Margin per unit

Breakeven Revenue = Fixed Cost / Contribution Margin %

Payback Period = Initial Investment / Annual Cash Flow

ROI = (Gain - Cost) / Cost

A common variant: the interviewer gives you a price increase and asks how much volume the client can afford to lose before the change hurts profitability. That is a breakeven question in disguise -- set up the equation and solve for lost volume.

ROIC (Return on Invested Capital = NOPAT / Invested Capital) shows up in PE diligence cases where the interviewer wants to assess operational efficiency relative to capital deployed.

NPV and time-value-of-money formulas

Net Present Value is the primary investment filter in capital allocation cases:

NPV = Sum of [Cash Flow / (1 + r)^t] for t = 1 to n

Two special cases to memorize:

Perpetuity value = Cash Flow / r (used when a business generates cash indefinitely at a flat rate)

Growing perpetuity value = Cash Flow / (r - g) (used when cash flows grow at rate g indefinitely)

Per the CFA Institute's time-value-of-money refresher, the perpetuity formula is the foundation of terminal value in DCF analysis -- which means it appears in PE diligence, infrastructure, and long-horizon investment cases even at the case-interview level.

The safe strategy: memorize the NPV formula and both perpetuity variants regardless of target firm. For PE-focused or restructuring interviews (Bain Capital, Parthenon, A&M), NPV fluency is required, not optional.

Market sizing shortcuts and ratios

Market sizing cases use a two-path structure. Choose the path based on which anchor number the interviewer gives you (or which one you can estimate more confidently):

Top-down: Market Size = Population x Penetration Rate x Purchase Frequency x Average Price

Bottom-up: Market Size = Units (stores, customers, firms) x Revenue per Unit

The full methodology is covered in market sizing framework. For the formula-focused view: the top-down path works when you know population and can estimate penetration. The bottom-up path works when you can anchor on a single unit (one store, one customer) and count up.

Common benchmarks worth memorizing for quick estimation:

These ranges come from Damodaran's sector dataset and standard SaaS benchmarks. When a case gives you a margin figure, they tell you whether you are looking at a healthy or distressed business without needing to ask the interviewer for context.

The 1-page memorization sheet and how to drill it

The most effective memorization approach is a single-page reference sheet organized by the six families, not by formula name. Build it in this order: Profit tree first, then contribution margin, then breakeven, then growth/CAGR, then market sizing paths, then NPV/perpetuity. The order matches case frequency.

For mental math speed -- rounding, percentage estimation, and approximation mechanics -- see case interview math mental shortcuts. That article covers the calculation techniques; this one covers what to calculate.

The drilling protocol: flashcard definitions for 3-5 days until you can write each formula from memory, then timed case math problems where you apply it within 60 seconds. The bottleneck is almost never formula recall -- it is translation speed (seeing a scenario and knowing which formula fits). That skill comes from repetition.

The Road to Offer consulting toolkit bundle includes a printed one-page math reference with the six families on one side and worked examples on the other.

Frequently Asked Questions

What formulas do I need to know for a case interview?

Six families cover around 90% of case math: profitability (Profit equals Revenue minus Cost and its disaggregations), pricing and contribution margin, growth and CAGR, breakeven and payback, NPV and time-value-of-money, and market sizing shortcuts. The contribution-margin formula is the single highest-leverage one because most case math chains back to it.

Are calculators allowed in case interviews?

Rarely. McKinsey, BCG, and Bain require mental arithmetic in the live first and final rounds. Some online assessments (BCG Casey, McKinsey Solve) provide an in-app calculator or scratch pad. The default assumption is no calculator unless the interviewer explicitly offers one.

What is the most important formula in a case interview?

Profit equals Revenue minus Cost, with the second-derivative tree underneath: Revenue equals Volume times Price, Cost equals Fixed plus Variable. Most profitability and pricing cases reduce to one or two pulls on this tree. The contribution-margin formula (Price minus Variable Cost per unit) is the next most-used.

How do I memorize case interview formulas?

Build a 1-page reference sheet, drill flashcards on definitions for 1 week, then run 10-15 timed cases focusing on math execution. Active recall beats re-reading. Across 14,000+ Road to Offer practice sessions, candidates who memorized contribution margin and breakeven first passed profitability cases at a 38% higher rate.

What math do I need for market sizing?

Top-down: Population times Penetration times Frequency times Price. Bottom-up: per-unit revenue times number of units (stores, customers, transactions). The Rule of 72 is useful for doubling time. Estimation accuracy matters less than visible structure on the way to the number.

Do I need NPV and IRR for case interviews?

For most generalist MBB cases, NPV and IRR show up in roughly 10-15% of cases (typically PE due-diligence or capital-investment cases). For tier-2 corporate-finance and PE-focused interviews (Bain Capital, Parthenon, A&M restructuring), NPV is required. Memorize the NPV formula, perpetuity, and growing perpetuity.

Sources and Further Reading (checked 2026-05-01)

• McKinsey Careers -- Tips for the case interview: https://www.mckinsey.com/careers/interviewing/the-case-interview
• BCG Careers -- Interview prep: https://careers.bcg.com/global/en/interview-prep
• Management Consulted -- 2025 Case Type Distribution: https://managementconsulted.com/case-interview/
• Damodaran (NYU Stern) -- Margins by sector dataset: https://pages.stern.nyu.edu/~adamodar/New_Home_Page/datacurrent.html
• CFA Institute -- Time Value of Money refresher: https://www.cfainstitute.org/insights/professional-learning/refresher-readings/quantitative-methods
• Road to Offer -- Platform data: 14,000+ practice sessions, contribution margin and breakeven memorization rate study