Went through BCG and Bain final rounds within the same month earlier this year. Both for associate/consultant-level. Here's what was actually different, not the stuff everyone already writes about.
BCG final round: Two cases plus a PEI (Personal Experience Interview). The cases skewed more quantitative in my experience. One was a classic profitability case with a multi-step market sizing component. The second was a M&A scenario that required some back-of-envelope NPV thinking. Your math needs to be fast and you need to narrate while you calculate, not go silent.
The PEI is genuinely important at BCG. Three themes they probe: leadership, personal impact, teamwork. You need distinct stories for each. They do follow up questions and they will poke holes if your story is vague. Had a partner push back with "but what did YOU specifically do" twice.
Bain final round: Also two cases but one of mine was a Bain-style written case where you read a bunch of slides and then present findings. That format requires different prep than a live case. You have to structure your time, synthesize quickly, and present confidently to a partner who is looking for business judgment not just analytical mechanics.
Bain's behavioral questions felt more culture-fit oriented. They care a lot about teamwork stories and seem to penalize answers that feel like solo-hero narratives. Frame everything as "we" with your specific role clearly identified.
What was similar: Both loops had partners who interrupted my case to go in a different direction. This is intentional. They want to see how you handle pivots. If you get defensive or lose your thread, that's a red flag.
Timeline: BCG was faster. Offer came 4 business days after the final round. Bain took 10 days, which I was told is normal for them.
Net: BCG = more quant pressure + rigorous PEI. Bain = more presentation format + teamwork framing. Both are hard. Prep for both even if you think you know which one you prefer.