Jane Street Interview Guide
How to crack the code at the world's most prestigious prop trading firm.
Jane Street is unique. They don't just ask you to calculate numbers; they ask you to bet on them. Their interview process is designed to test your intuition for Expected Value (EV) under uncertainty. Unlike other firms that might focus on obscure math tricks, Jane Street cares about how you think and how you communicate your thought process.
The Roles
Jane Street hires primarily for three technical roles. Knowing which one you fit into is step one.
- Quantitative Trader: The person making the decisions. You will be managing risk, updating parameters, and communicating with the team. Interviews focus on probability, betting games, and rapid mental math.
- Quantitative Researcher: The person building the models. You will use data (mostly Python/OCaml) to find signals. Interviews focus on statistics, data analysis, and deeper math.
- Software Engineer: The person building the systems. Jane Street is famous for using OCaml. You don't need to know OCaml beforehand, but you need to be willing to learn. Interviews focus on algorithms, functional programming concepts, and systems design.
The Interview Process
The funnel is standard, but the questions are not.
Stage 1: The Screen
Usually a mental math screen (e.g., arithmetic in your browser) or a recruiter chat. For SWEs, it might be a HackerRank style OA.
Stage 2: Phone Interviews (1-2 Rounds)
These are 45-minute technicals. For traders, expect a probability puzzle. Example: "I roll a die. Only even numbers count. What is the expected value of the sum until I get a 6?"
Stage 3: The Onsite (Superday)
3-4 back-to-back rounds. This is where it gets intense. You will play "market making" games where the interviewer acts as the market and you have to quote prices.
Detailed Question Walkthroughs
1. The "Make Me a Market" Game
The Question: "Make me a market on the number of windows in this building."
What they are testing: Not your window-counting skills. They are testing your ability to create a confidence interval and update it based on new information.
The Strategy:
- Fermi Estimate: "This building has 40 floors. Each floor is maybe 100x100 meters..." → "I estimate 2000 windows."
- Set Width Confidence: "I'm not very sure. So my 90% confidence interval is [1000, 3000]."
- Listen to the Bid/Ask: If the interviewer buys at 3000, they think there are MORE. You must shift your market up immediately!
2. The "Biased Coin"
The Question: "I have a coin that lands Heads with probability $p$. I flip it $N$ times. What is the probability I get exactly $k$ heads?"
What they are testing: Your command of the Binomial Distribution formula: $\binom{n}{k} p^k (1-p)^{n-k}$. They might then ask: "What happens to this probability if $N$ goes to infinity?" (Central Limit Theorem intuition).
Compensation & Perks
Jane Street is consistently top-of-market.
- New Grad Base Salary: Typically $200k - $250k.
- Signing Bonus: $50k - $100k.
- Performance Bonus: This is the big one. Can range from 50% to 100%+ of base salary. First year total compensation (TC) often exceeds $400k.
- Perks: Free breakfast, lunch, and dinner. Incredible office views. A culture that encourages intellectual curiosity (chess tournaments, puzzle hunts).
Culture: "Intellectual Honesty"
The biggest cultural value at Jane Street is "Intellectual Honesty". It means being willing to admit you are wrong immediately. If you make a bad trade, you don't hide it—you fix it and learn. In the interview, if you realize your math is wrong, say so! "Wait, that doesn't make sense because..." is a positive signal, not a negative one.
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