The Ultimate Guide to YCombinator Interview Preparation

During my own preparation for Winter 2018 class interviews, I’ve reviewed every public resource on the topic and did over 20 practice interviews with Y Combinator alums. Everything I’ve learned is summarized below. This guide is my personal take and doesn’t represent an official position of YC.

Answers development

Answers document. The core of your preparation process is writing a document with all anticipated questions and your answers to them. Start with the items below, then expand by adding answers to new questions asked at your practice interviews.

Opening description. Your first sentence in the interview is either a solution description or value proposition. It should be 4–8 words long and pass the “mom’s test”, i.e. your parents should be able to repeat it back to you.

Strength points. Define 3 core strength points in advance. Steer conversation to hit them all, sometimes even regardless of questions.Types of strength: revenue/growth/traction, domain expertise/done this before, insight aka “a-ha moment”, market size.Consider repeating or rephrasing your top three points when you aren’t sure they landed well the first time.Test your strength points: Will someone be excited about your company if she/he only hears the one-line description and three strength points?

Insights. Those are anecdotes, quotes, or factoids that receive consistent “a-ha” and “hmm.. interesting” reactions during your practice runs.

Defense. Know your 2–3 key weakness areas and prepare short, crisp answers to most common concerns.For every question that you don’t answer with a strength point or an insight, limit yourself to one sentence. You want to maximize the time for strength discussion, not secondary issues. If you use the second sentence, it should go back to strengths or insights.

How to write strong answers

Use a lot of factoids and numbers. Your answers document should have at least 20–30 answers with numbers. Whenever possible, eliminate verbs from answers. E.g. “What’s your go-to-market?” — “A, then B, then C”.Use simple words and examples, avoid buzzwords or abstract concepts. For questions on weakness areas, acknowledge or defend it in one sentence, then go back to strengths in the second. Use examples and facts over forward-looking plans. “In the past, we’ve solved it by X with results Y”.Explain implications: “if we achieve X (hard, but possible technical achievement), then we will get Y (major business win)”. Whenever possible, use primary data from customers instead of analogies. Generally, YCombinator doesn’t see analogy-based arguments as reliable or strong.Avoid top-down market sizing. Either do bottom-up or close comparables. “Sell your co-founder”, be ready to tell why your partner is great.

Practice runs

Schedule at least 10–20 practice runs. For mock interviews, ask investors and founders you already know, YC alums from your city / country / university, YC alums in your industry or with a similar business model, and YC alums who volunteer to do practice interviews on Twitter. You don’t need an intro. Ask early, at least 7–10 days before your interview day.

Take notes and rewrite your answers after each practice run. Do a debrief with each mock interviewer. Ask which answers were clear and strong, and which ones were not. Discuss how to improve your individual answers. Iterate on your top strength points, unique insights/anecdotes, and defense answers.

Additionally, watch YC’s public office hours (links below) to get a feel of YC interview format.

Interview day

Logistics and expectations. Arrive early, identify your room and learn who is on your panel, research panel partners in the remaining time. Make new friends with fellow applicants. Have the demo ready on the laptop with all important screens in multiple tabs. Don’t rely on YC WiFi.Assume that YC partners have no prior knowledge. Review partner’s bios in advance, identify partners who can become supporters due to their personal interest in your space. From YC’s standpoint, the purpose of the interview is to extract as much info as possible in 10min. At least one of YC partners will look closely for body language and nonverbal signals. Expect 40–80 questions in 10 minutes, 8–12 seconds per question-and-answer round. Be ready for constant interruptions (even after the first 2–3 words of response). Be ready for unique questions outside of your list. Be ready for parallel interview with multiple co-founders (not very common). Be ready for a narrow and deep drill on a single question, most likely related to your biggest weakness.

Interview time. Talk fast, but not super fast. Feel happy, high-energy, and excited to pursue the opportunity. Be casual and friendly, maintain eye contact. Be confident, yet humble. Confident and concise = formidable. A few weak answers are ok. A long weak answer is much worse than a short acknowledgment like “I don’t know” or “we plan to work on this”. Don’t be too defensive, show coachability. Consider repeating or rephrasing your top three points, if they weren’t well received the first time. Most answers should be one sentence, some can be two sentences. Limit yourself to only 2–3 longer replies throughout the interview. Don’t interrupt each other, don’t argue on unexpected questions. Instead, say “yes and …” or “and I’ll add to this…” to continue after your co-founder. When disagreeing with YC partner’s statement, either give counter-facts or accept it as a hypothesis to test. Don’t make straight deflections. Answer the question asked, before changing direction. When challenged on critical hypotheses for your business, be ready to push back with crisp defense and facts. When the conversation goes sideways, try to steer it back to strengths, e.g. “and I want to make sure you hear this…”.

Expected YC evaluation criteria. Interesting problem. Ideally, unique or novel. Otherwise, a new insight or approach. Compelling value proposition. Clear and concise solution description. Clarity on how the hard parts of the solution work. Inspiring mission. Market size and dynamics. A small but rapidly growing market is always compelling. Insightful ideas for overcoming market-specific concerns. Activation of “spidey sense” i.e. “hmm… something interesting should happen in this space” feeling. Team with deep relevant expertise and domain knowledge. Strong communication skills: crisp, short, clear answers. Competitive landscape fluency. Proven rapid pace of making progress. Energy and resourcefulness, “get things done” attitude. Coachability, being good at taking feedback constructively. Determined, yet flexible. Original thinking and learning ability. Unconventional points of view and insights directly from customers. Positive team dynamics, no interruptions or arguing, alignment on vision. Low chance of founder conflict. Good English and easy-to-understand accent, no language barriers in communication. Ability to inspire and recruit star team. Make YC partners want to work for you. Can grow into “forces of nature”. Direct path to building momentum by the end of YC program aka “become a hot seed deal”. Direct path to hitting high revenue in 2–3 years aka “getting big”.

Y Combinator Interview Resources


I am forever grateful to everyone who helped us through the process: Hrachik Adjamian, Daniel Ahmadizadeh, Andrew Arruda, Delian Asparouhov, Chas Ballew, Kirill Belov, Eva Breitenbach, Matt Brezina, Tom Broderick, Levon Brutyan, Jeremy Cai, Dan Carroll, Deepak Chhugani, Nick DeMonner, Dmitry Dumik, Evan Farrell, Herbie Fu, Jim Gibbs, Anton Gladkoborodov, Allan Grant, Vlad Gurgov, Chetan Jhaveri, Ryan Johnson, Dave Kim, Alexander Kim, Kwindla Hultman Kramer, Sam Lang, Clarence Leung, Bowen Lu, Max Musing, Ivan Novikov, Thomas Pun, Roberto Riccio, Wen Sang, Boris Silver, Preston Silverman, Zac Townsend, Brett Van Zuiden, James Vaughan, Praveen Venkatesan, Tracy Young, Diana Zink.

Good luck!

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