10 Jane Street Quantitative Research (New Grad) Interview Questions (2026)
Jane Street's new-grad quant research loop in 2026 is a coding test, a phone interview, and a multi-round virtual onsite covering probability, mental math, brainteasers, and trading-game mechanics. The bar on math intuition under time pressure is the dominant signal — interviewers care less about whether you remember a specific identity and more about how you reason out loud.
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Loop overview
Typical flow: recruiter outreach → 90-min coding/math screen → first-round probability phone interview (45 min) → onsite of three to five rounds: probability deep-dive, market-making game, mental math sprint, sometimes an OCaml or systems chat, and a fit conversation. Most reports indicate a 4-7 week timeline. Onsites in 2026 are predominantly virtual with optional in-person final at the NY office.
Behavioral (3)
You are market-making on a coin that lands heads with unknown probability p. Bid-ask is your decision. How wide do you quote initially, and how do you update?
Frequently askedOutline
Show meta-thinking: start with a wide spread because you have no information. As trades occur, update via Bayesian intuition — if customers keep buying, p is likely high, raise the bid. Discuss adverse selection (informed traders). Don't try to be exact — interviewers want to see structured reasoning about uncertainty, market microstructure, and risk.
Tell me about a time you made a mistake on a project. What did you learn?
Frequently askedOutline
STAR. Pick a real mistake — Jane Street has a low tolerance for storytellers who can't admit fault. Focus on the introspection: what was your blind spot, how did you catch it, what is your check now. Quant culture rewards epistemic humility.
Why Jane Street rather than a tech company?
Frequently askedOutline
Honest, specific reasons: love probabilistic reasoning, want immediate feedback loop on decisions (P&L), interest in mid-size firm with no clients, attracted to functional programming culture (OCaml). Avoid 'high pay' as the lead. Demonstrate you understand the cost: high intensity, narrow career path early.
Coding (LeetCode patterns) (1)
Write a function that simulates flipping a biased coin (p=0.6) using only a fair coin.
Occasionally askedOutline
Generate uniform random in [0,1) from fair coin flips: each flip is a bit; build a binary fraction. Stop when the partial value is clearly above or below 0.6. Worst case unbounded but expected ~2-3 flips. Mention rejection sampling alternative. Discuss expected number of flips and termination guarantee.
Technical (6)
I roll two fair six-sided dice. What is the probability that the sum is 7, given that at least one die shows a 3?
Frequently askedOutline
Conditional probability. P(sum=7 | at least one 3) = P(sum=7 AND at least one 3) / P(at least one 3). Sum=7 with at least one 3 happens for (3,4) and (4,3) = 2/36. P(at least one 3) = 1 - (5/6)^2 = 11/36. Answer: 2/11. Walk through the sample space explicitly — interviewer wants to hear you enumerate.
A fair coin is flipped until you see two consecutive heads. What is the expected number of flips?
Frequently askedOutline
Standard Markov-chain expected-value problem. Let E0 be expected flips from no progress and E1 from one head so far. E0 = 1 + (1/2)E1 + (1/2)E0; E1 = 1 + (1/2)(0) + (1/2)E0. Solve: E1 = 1 + E0/2 and substitute. Answer: 6. Draw the state machine on paper to avoid algebra errors under pressure.
I am offering a game: roll a fair die; you may take the dollar amount on the die, or re-roll. You can re-roll up to twice. What is the fair price of this game?
Frequently askedOutline
Backward induction. Last roll value is uniform on {1..6}, expectation 3.5. Second-to-last: keep if face > 3.5 (so >=4), else reroll for E=3.5. E2 = (5/6)·avg(4,5,6) + (1/6)·avg(1,2,3)... actually: P(keep)=3/6, average kept = 5; P(reroll)=3/6, E=3.5. So E2 = 0.5·5 + 0.5·3.5 = 4.25. First roll: keep if >=5, average kept = 5.5; else reroll for 4.25. E1 = (2/6)·5.5 + (4/6)·4.25 ≈ 4.67. State the framework cleanly.
What is 47 × 53 in your head?
Frequently askedOutline
Difference-of-squares trick: 47×53 = (50-3)(50+3) = 2500 - 9 = 2491. Practice these patterns; interviewers expect <5 seconds. Other common pairs: 96×104, 28×32, 19×21. State the algebraic identity briefly, then the answer.
Two players take turns drawing one ball from an urn with 3 white and 3 black balls, without replacement. The first to draw a black ball wins. You go first. What is your probability of winning?
Occasionally askedOutline
Enumerate paths. P(win on turn 1) = 3/6 = 1/2. P(win on turn 3) = (3/6)(2/5)(3/4) = 6/40. P(win on turn 5) = (3/6)(2/5)(1/4)(3/3)... compute carefully. Total your wins: 1/2 + 6/40 + smaller terms. Alternative: recursion with state (white_left, black_left, whose_turn). Mention both and pick one. Final answer ≈ 0.65.
You have 100 prisoners and 100 boxes, each with a unique prisoner's name. Each prisoner can open 50 boxes. If every prisoner finds their own name, all are freed. What strategy maximizes survival probability?
Occasionally askedOutline
Classic 100-prisoners puzzle. Each prisoner starts at the box matching their own number, then follows the chain (open box, read name, next box matches that name). All survive iff the random permutation has no cycle of length > 50. P(success) ≈ 1 - ln(2) ≈ 0.31. State the cycle insight first, then derive the bound from harmonic sums.
Jane Street interview tips
- Mental math is non-negotiable. Drill multiplication of two-digit numbers, percent conversions, and quick probability fraction arithmetic until it is reflexive.
- Talk through your reasoning continuously. Silence under time pressure scores poorly. State assumptions, restate the question, work through cases.
- For market-making rounds, embrace wide initial spreads. Tighten only as you receive flow. Interviewers test whether you panic-update or stay disciplined.
- Probability puzzles often have an elegant symmetry trick. Before grinding through algebra, ask 'is there a complementary event or invariant that simplifies this?'
- OCaml exposure is a bonus, not a requirement. If you list functional programming on your resume, expect a question on immutability or pattern matching.
Frequently asked questions
How long is Jane Street's quant research interview process in 2026?
Most candidates report 4-7 weeks from initial contact to offer. Strong performers move faster; brainteaser rounds can compress to a single intense onsite day.
Does Jane Street require knowledge of finance for new-grad quant research?
No. The interview tests probability, statistics, and quantitative reasoning. Finance knowledge is a plus only in the fit conversation.
What programming language should I use for Jane Street coding rounds?
Python is universally accepted. OCaml signals strong cultural fit since it is the firm's primary language, but you will not be penalized for choosing Python.
How does Jane Street compare to traditional Wall Street roles?
Compensation is comparable to top-tier banking but the day-to-day is closer to applied research — small teams, fast iteration, immediate P&L feedback. No client work, no pitch books.
Can I retake Jane Street's interview after rejection?
Yes. There is typically a 12-month cooldown before re-interviewing. Recruiters track which rounds you previously failed and may skip you ahead in the next loop.
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