Optiver Phone Screen: Mental Math, Probability, and How to Pass It

You've applied to Optiver. Congratulations on your optimism.

Most guides get this wrong: what people call the "Optiver phone screen" is really a two-stage ordeal. First, a timed online assessment that filters out about 80% of applicants before a recruiter reads a single word of your resume. Then, if you survive, a 30-minute call that is essentially a vibe check. The OA is the phone screen. The phone screen is the celebration lap.

If you are prepping for this like a normal behavioral call, you have miscalibrated. Badly.

The Process Is Not What Most Guides Describe

Stage	Format	Duration	Filter Rate
Resume review	Automated + recruiter	Days	Moderate
Online assessment	3 timed sections	~2.5 hours	Very high (~80%)
Recruiter phone screen	Behavioral call	30 minutes	Low
Onsite ("Super Day")	4 components	Half day	Moderate

The OA is where most candidates are eliminated, not the phone call. Treat the recruiter screen as confirmation that you passed, not as the primary hurdle.

Section 1: Your Brain Has 6 Seconds Per Question

Eighty questions. Eight minutes. Six seconds each. No calculator. No mercy.

The topics are not exotic. Four basic operations, fractions, percentages, ratios, basic probability. "47 × 23." "What is 7/8 as a percentage?" "A trader has $1,240 and loses 15%. How much remains?" Nothing conceptually hard. All brutally fast. The entire section is designed to find out if your brain has RAM, and then test it under conditions that simulate having a coffee right before a fire alarm.

Scoring is a penalty system: +1 correct, -1 wrong, zero for skipping. That last part matters more than it sounds. Guessing costs you. Most candidates do not fail because they get answers wrong. They fail because they move cautiously through the first half, run out of time, panic, guess on the back stretch, and get penalized for all of it.

Skip anything you cannot answer in three to four seconds. Return only if time allows. This is not humble caution; it is the actual optimal strategy.

The arithmetic shortcuts are the whole game here. 47 × 23 becomes (50 − 3) × 23 = 1,150 − 69 = 1,081. Fifteen percent is 10% plus half of that. Seven-eighths is 1 − 1/8 = 0.875. Each shortcut saves one to two seconds, which compounds across 80 questions into the difference between clearing the threshold and not.

The pass threshold is around 55 out of 80. Competitive candidates aim for 70. To hit 70, you need weeks, not days. Use Zetamac every morning for 15 minutes. Target 80 correct in 8 minutes at 90%+ accuracy before you even apply. Most successful candidates report three to four weeks of this. There is no shortcut here. The test literally exists to check whether you have put in the reps.

Section 2: "Beat the Odds" Tests If You Actually Understand Probability

Ten questions, 15 minutes, roughly 90 seconds each. The section sounds friendlier than "80 in 8." It is not friendlier. It just kills you with reasoning instead of speed.

Common types:

Expected value: "If I flip a coin until I get heads, what is the expected number of flips?"
Conditional probability: Card draw scenarios, dice problems requiring Bayes' reasoning
Combinatorics: Arrangements and selections with or without replacement
Game scenarios: Tennis probabilities, gambler's ruin, die optimization

The coin-flip question is geometric distribution: E[flips] = 1/p = 1/0.5 = 2. You should arrive at that in seconds, not after a long moment of staring at the ceiling. The section rewards fast probabilistic intuition backed by correct first-principles reasoning. If you need more than 60 seconds to set up the problem, you are already behind pace.

Optiver's careers site has a practice version of this test. Use it before your OA. It is the closest thing to the real environment you will find short of actually taking the OA.

Prep depends heavily on your background. Stats or math degree? Review expected value derivations, Bayes' theorem, and basic discrete distributions, and you should be fine. Software background with minimal stats? Spend at least two weeks with a probability textbook before the test. General reasoning ability does not substitute for the specific fluency this section requires.

Section 3: The Coding Part Has One Trap Most Engineers Walk Right Into

Two programming problems on HackerRank. LeetCode medium difficulty: LRU Cache, removing duplicates from a sorted array, finding the majority element.

Python is not accepted. Optiver supports Java, C++, C#, C, and Ruby. That's it.

This is the restriction that produces a particular kind of suffering among engineers who have spent years defaulting to Python for everything algorithmic. You have 80,000 lines of Python muscle memory, you open HackerRank, and the language selector does not have what you want. This is not the moment to learn Java under time pressure.

If Python has been your LeetCode language, start solving problems in Java or C++ now. Not the week before the OA. Now.

The evaluation focuses on correctness and efficiency. Brute-force solutions with poor time complexity score lower than optimal implementations even when both produce the right output. Know your standard library for whatever language you pick: how to use a PriorityQueue in Java, how to use unordered_map in C++. Do not reinvent wheels under time pressure.

One bookkeeping note: the three OA sections share an overall time budget. If you spend too long on the coding problems, you are borrowing time from the probability section. Budget deliberately.

For what comes after the OA, see the Optiver software engineer interview guide. The coding section here is medium difficulty; the onsite goes deeper.

The Phone Screen: The Part That Does Not Want to Kill You

Pass all three OA sections and a recruiter contacts you within one to two weeks for a 30-minute call. Behavioral, not technical.

Typical questions:

Walk me through your background
Why Optiver specifically?
Describe a project you are proud of and the impact it had
What are you looking to develop in your next role?
How would teammates describe you?

The phone screen is a fit and motivation check, not a second technical filter. The recruiter is confirming that the person they are about to invest onsite time in actually wants to work at Optiver and can communicate clearly. That is a low bar. Clear it.

Prepare one or two project examples with real numbers: "reduced latency by 40%," "shipped a feature used by 50,000 traders." Know why Optiver appeals to you beyond "it pays well." That answer reads as shallow. Research their market-making operations and what differentiates them from Jane Street or Citadel. Optiver makes markets in options and ETFs. Understanding what that means at a basic level signals genuine interest, and the recruiter will notice if you clearly googled it the night before.

Use STAR format for behavioral stories: Situation, Task, Action, Result. Keep each answer under two minutes.

What Actually Gets You Eliminated

Each OA section is scored independently. Failing one eliminates you regardless of how well you did on the others. A 79/80 mental math score does not compensate for a weak probability section. The sections do not negotiate with each other.

Below around 55 on the mental math test is a hard cutoff in practice. The probability section has similar gates, though Optiver does not publish the exact thresholds. The coding section is graded by test case pass rate and code quality.

One pattern candidates report: passing all three automated sections and still receiving a rejection with no feedback before any recruiter contact. There appears to be additional automated screening at the application stage. Optiver also uses personality and cognitive assessments, labeled Zap-Q and Zap-N, that some candidates encounter. If you see these, take them seriously. Optiver emphasizes collaborative problem-solving alongside raw ability.

The reapplication restriction is real: unsuccessful applicants face an eight-month waiting period before reapplying to similar roles. Eight months. Treat every section accordingly.

A Realistic Prep Timeline

If you have four weeks before your OA:

Week 1: Daily Zetamac sessions (15 minutes each), targeting speed first. Solve 10 probability problems from first principles. Review expected value, conditional probability, and basic combinatorics.

Week 2: Simulate the 80-in-8 daily under exact conditions. Practice Java or C++ on LeetCode mediums, no Python. Do 20 probability problems timed at 90 seconds each.

Week 3: Full OA simulation using Optiver's provided practice tools. Find your weakest section and concentrate there. Prepare two to three STAR stories for the recruiter call.

Week 4: Light review and full practice runs. Focus the recruiter prep: why Optiver, your best project story, what you want to grow.

Once you clear the OA and are heading into the onsite, SpaceComplexity runs AI-powered voice mock interviews with rubric-based feedback on communication, problem-solving, and technical accuracy. That kind of practice helps more than grinding additional LeetCode once the OA is behind you.

For other quant firms, quant interview prep covers how Optiver's format compares to Jane Street or Two Sigma, both of which lead with probability-heavy screens rather than speed arithmetic.