Master case interview math, under pressure.

Numbio is a mental math trainer for consulting candidates. Timed drills on the arithmetic that actually shows up in McKinsey, BCG and Bain cases: percentages, ratios, money, large numbers, fractions. Five minutes a day, no calculator, no paper.

Practice the math that gets you hired at top firms:

Practice the math that gets you hired at:

$Three Numbio exercise cards: multiplying whole numbers, multiplying euro amounts, and a fraction task$

Trusted by Thousands Worldwide

More than 40,000 people open Numbio every month, in over 40 countries, and it has earned over 5,000 five-star ratings along the way.

Smiling young man in a gray suit and light blue tie on a cream background

Daniel S.

May 1, 2025

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Germany

I could structure a case but kept stalling on the arithmetic inside it. Five minutes of daily drills moved the math into reflex. By my final round I was thinking about the business problem instead of the numbers.

Pauline0987
May 3, 2025
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Germany
“It really helped me with my case interview preparation, brushing up my mental math. The leaderboards keep you training.”
Eb7.1262
Sep 12, 2024
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France
“Perfect application for training during strategy consulting interviews.”
D_st1.98
Feb 10, 2026
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Germany
“Ideal for preparing for an aptitude test with demanding mental arithmetic questions… even in the free version.”
vane_btw
Dec 13, 2024
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Germany
“I’m using the app to prepare for an aptitude test, and it has got me further already.”
VVN Kumar
Feb 10, 2026
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India
“Very useful for those who are preparing for competitive exam. Helps a lot in increasing speed.”
Moniika_12_
Jul 14, 2024
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India
“I am preparing for bank exams and this app is helping me so much in improving my calculation speed.”

4.6

8K+ Ratings

1 M+

Users Globally

Trained Out Loud

Case math is heard and answered aloud, never typed into a screen. Numbio reads exercises to you, blurs the numbers, and takes your spoken answer, so the interview room isn't the first time you do it live.

Numbio exercise card with the numbers blurred out and a speaker icon, while a spoken answer, "thirty-six", is marked correct.

Numbio trick card solving 36,000 × 250 by multiplying by 1,000 and dividing by 4, with 9M marked correct.

Big numbers, made simple

Cases don't run on times tables. Learn the mental math tricks that crack five-digit multiplication and quick percentages, then drill each one until the awkward numbers stop being awkward.

Close enough counts

Interviewers want a defensible estimate in seconds, not four decimal places. Numbio's tolerance setting accepts answers that are close, so rounding becomes a skill you train on purpose.

Numbio estimation card for 4,870 × 21 where the answer 100K is accepted because it falls within a ±5% tolerance band.

Numbio percentile chart comparing your 0:47 time with your age group, placing you in the top 12% of players.

Know where you stand

Guides can't tell you if you're ready. Numbio can. See how your speed ranks against your age group and players worldwide, and watch the number climb as you close in on interview pace.

Every calculation a case throws at you

Drills for each type of case math, plus the tools that tell you when you're ready.

Percentages

Growth rates, margins and market shares.

Huge numbers

Millions and billions, for market sizing.

Money and decimals

Prices, unit costs and revenue per customer.

Fractions

Reduce and compare them without paper.

Rule of three

Ratios and proportions for scaling any number.

Chain calculations

Keep a result in your head across steps.

Custom trainings

Build a set around your weakest operations.

AI trick picks

Shortcuts chosen for the mistakes you make.

Daily reminders

Five minutes a day, up to your final round.

Crunch the Numbers Before They Crunch You!

Try it free and start sharpening your case math today.