MBB vs Big 4: what's actually different

1. MBB firms are far smaller — which is why they're more selective

This is the fact that explains most of the others. The top three strategy firms are roughly a tenth of the size of the Big 4.

As of 2018, McKinsey had around 27,000 employees, BCG around 20,000 and Bain around 8,000. Deloitte, PwC, KPMG and EY each employed somewhere between 200,000 and 300,000 people.

The consequence is arithmetic. The Big 4 must recruit a very large number of people every year just to sustain their size. MBB need far fewer. So purely as a numbers game, MBB are more selective — not necessarily because the people are categorically different, but because there are fewer seats.

Worth knowing, though: the Big 4's consulting divisions are bigger than MBB — by headcount and by revenue. For Deloitte and PwC in the UK, consulting is among the largest revenue drivers, bigger than audit. The "Big 4 are just accountants" line is a decade out of date, and some of their own clients still believe it.

2. Strategy versus implementation — mostly true, often overstated

Most of what McKinsey, BCG and Bain do sits on big strategic questions: strategy, organisation, marketing, operations, digital, M&A. C-suite problems. They don't offer audit, assurance or tax.

The Big 4's consulting work is concentrated in Advisory and skews towards implementation — answering "help me do it" rather than "what should I do". Rolling out a new process or technology across a business, restructuring business units, running the transformation. Which means Big 4 consultants more often work with the client's middle management than its C-suite.

But the Big 4 absolutely do strategy — Strategy& at PwC, Monitor at Deloitte. It's a smaller share of revenue, and those arms were often acquisitions rather than the core business. Consultants there work across sectors much like MBB.

A warning from my own career, though: I nearly turned down tech consulting because I'd heard it was "just implementation". That was wrong, and it would have cost me the way in.

3. Generalist versus specialist — the difference that shapes your career

This is the one that actually changes what your life looks like, and almost nobody weighs it properly.

Big 4 consultants often spend 6–12+ months on the same client, embedded almost like an employee. You specialise in an industry early. The work can get repetitive — but you develop real depth, and you're still there to see whether what you recommended actually worked.

MBB consultants typically spend 2–4 months on a client, sometimes less, and rarely specialise until much later. The work is more varied. You also frequently leave before your recommendation meets reality.

Neither is better. They suit different people. If you get bored quickly and want breadth, the shorter cycle is a gift. If you want to own an outcome and become genuinely expert in something, the longer engagement is.

So which should you go for?

Go for the one that matches how you want to work, not the one with the better logo in a group chat. And if you're choosing between an offer in hand and waiting a year for a "better" firm — take the offer. A year is an expensive way to buy prestige, and you can always move.

I got into the Big 4 with no business degree and no consulting internship, in tech consulting I initially didn't even want. It worked out.