California Institute of Technology Supplemental Essay Prompts & Writing Guide 2025-2026

When approaching this prompt, treat it as a straightforward "Why Major?" essay that's grounded in your genuine intellectual interests. Caltech explicitly states that you're not locked into the major you choose, since all first-year students take the same rigorous core curriculum and don't declare majors until sophomore year. The admissions committee simply wants to see that you can articulate clear academic interests and that those interests align with the rest of your application.

Start by being honest: select the one or two majors that genuinely excite you right now, based on your actual experiences and curiosities. Don't try to strategize by picking an uncommon major to stand out or gaming the system to seem unique. Authenticity matters at Caltech, and any attempt to misrepresent your true interests will come across as insincere to admissions readers. Your selected majors should align with the STEM activities, projects, and coursework already listed elsewhere in your application. If you've done research in computational biology or taken advanced chemistry courses, those connections should naturally lead to your major choice.

For the "why" portion of your response, focus on specific moments or experiences from your high school years (not childhood stories) that sparked your interest in these fields. Maybe it was a particular experiment, a challenging problem you couldn't stop thinking about, or a research paper that opened your eyes to new possibilities. Use concrete details about what aspects of the field fascinate you, whether it's specific concepts, techniques, or unsolved problems. Keep your writing efficient given the tight word count: dive straight into your story rather than spending precious words on elaborate hooks. Caltech faculty members, who often review competitive applications, will understand advanced technical language, so don't dumb down your explanations. Show depth by discussing what still puzzles you or what questions you're eager to explore further, demonstrating that you're intellectually curious rather than someone who thinks they've already learned everything.

This is your chance to show Caltech that you pursue STEM knowledge independently and for the sheer joy of discovery. Choose a topic you genuinely find fascinating right now, something you recently binged videos about, read obsessively, or explored through late-night coding or problem-solving. Caltech wants to see what captivates you beyond your primary academic focus, so pick something that reveals a different facet of your intellectual curiosity. Whether it's knot theory, the topology of DNA replication, solar cell design, or the mathematics behind black holes, your topic can be as niche or as broad as you like, but it must reflect authentic enthusiasm.

You have just 50 to 150 words, so don't waste time on background or setup. Jump straight into what pulled you down this rabbit hole and what you found compelling along the way. Use specific details: mention particular concepts, resources you consulted (papers, textbooks, simulations), or surprising connections you discovered. For instance, if you explored fractal geometry, explain what specific property or application fascinated you (maybe how fractals model coastlines or vascular systems). Keep your tone energetic and personal. Caltech faculty review these essays, so you can use technical language without oversimplifying, but remember that clarity matters more than showing off jargon.

Finally, resist the urge to force a connection to your intended major or career goals. This essay is about intellectual play and curiosity for its own sake. Admissions readers want to sense your excitement, the kind that makes you lose track of time. If your rabbit hole led to a project, experiment, or ongoing investigation, mention it briefly to show initiative, but the focus should remain on what ignited your interest and why you find it irresistible.

Caltech is looking for students who are genuinely obsessed with STEM, so your essay should dive deep into the specifics rather than skim the surface. Don't worry about whether your topic sounds impressive or overly technical: faculty members with PhDs review the most competitive applications, so you can use advanced terminology and explain complex concepts without dumbing them down. In fact, the admissions team explicitly encourages applicants to "nerd out" and write about the "STEMiest of STEMmy topics" because this helps them identify students who have intellectual vitality and curiosity.

If you choose the first prompt (how you found your passion), start with a specific moment or experience that ignited your interest: maybe it was a failed experiment, a concept you couldn't wrap your head around, or an unexpected discovery that made you see science differently. Then, trace how you pursued this interest over time through self-directed learning, independent projects, competitions, research, or even just persistent exploration outside of class. Caltech wants to see initiative and evidence that you actively seek out opportunities to deepen your understanding, so highlight the steps you took on your own (teaching yourself a programming language, designing experiments at home, reading research papers, or building something from scratch).

If you choose the second prompt (a meaningful STEM experience), focus on one significant moment from the last few years and explain both what happened and why it inspired your curiosity. This shouldn't just be a summary of a project or achievement: dig into the intellectual impact. What question did this experience raise for you? How did it change the way you think about a problem or field? Did it lead you to explore a new area or reconsider something you thought you understood? Connect the experience to your ongoing curiosity and show that it sparked deeper inquiry rather than just checking a box.

With only 100 to 200 words, be ruthlessly specific. Cut generic language and filler, and instead use precise, active verbs and concrete details that convey your enthusiasm and intellectual depth. Choose a narrow slice of your STEM journey rather than trying to cover everything, and make sure your essay reveals something new about you that isn't already apparent elsewhere in your application. Authenticity matters more than polish: Caltech wants to see who you are as a scientist, mathematician, or engineer, so write in your own voice and let your genuine passion come through.

This prompt gives you the chance to showcase your hands-on problem-solving mindset and creative spirit. Caltech is unapologetically STEM-focused, and your response should dive deep into the technical details. Think about a time when you saw a problem, got curious, and invented your own solution, whether it involved building an app, tweaking a bike part after hitting a pothole, designing a chemistry study tool, or even experimenting with a new cooking technique. The admissions readers want to see that you approach challenges with curiosity and initiative, not just memorized formulas or textbook knowledge.

Don't feel pressured to write about some award-winning research project or groundbreaking invention. Caltech celebrates everyday innovation and values applicants who demonstrate a maker's instinct in their daily lives. The prompt specifically mentions smaller-scale innovations like 3D-printing dorm decor or trying new recipes, so feel free to write about something personal and authentic that truly matters to you. What's crucial is showing the motivation behind your innovation: did you notice a gap that needed fixing, were you fascinated by an underlying scientific principle, or did a personal experience drive you to create something new?

Make sure to explain the "why" behind your creative work, not just the "what." Admissions readers want to see your thought process and understand what sparked your interest in the first place. If you designed a new study tool, describe what problem you were trying to solve and how you approached it step by step. If you coded an algorithm to optimize something, detail your reasoning and how you iterated through challenges. Focus on specificity and use technical language confidently (remember, Caltech faculty review these essays and will appreciate depth). Also, avoid generic claims: instead of saying you "love problem-solving," demonstrate it through a vivid, concrete example of how you tackled a challenge head-on.

Finally, connect your innovation to your future at Caltech by hinting at how this mindset will continue to drive your work in college. Whether you're excited to collaborate on research, contribute to interdisciplinary projects, or keep experimenting with new ideas, show that you're already thinking like a Techer who won't stop asking questions and building solutions.

The most strategic move you can make with these two short essays is deciding how to allocate your 250 words. Think carefully about which two prompts will let you reveal something fresh that hasn't been covered elsewhere in your application. If your Common App essay and other Caltech responses already highlight your STEM journey in depth, consider using these 250 words to showcase personality traits, non-STEM interests, or identity dimensions that admissions hasn't yet seen. The flexibility is intentional: you could write 125 words on each, or split it 80-170, or even 40-210 if one topic demands more depth. Just make sure both responses add distinct, complementary value.

Caltech openly encourages applicants to write about non-STEM topics here ("If you're all STEMmed out, feel free to tell us about a creative hobby"), so don't feel obligated to force a science angle into every answer. That said, you can absolutely lean into STEM if that's where your genuine passion lies ("Or if you just can't get enough math, tell us about a concept you can barely wrap your head around"). The key is authenticity. Whether you discuss rock climbing, origami engineering, your identity as a first-generation student, or a mind-bending physics concept, your enthusiasm and voice should come through clearly. Caltech's admissions team reviews thousands of essays, so specificity and genuine excitement will make you memorable.

Since you have such limited space, get to the point immediately. Avoid long introductions or generic statements. If you're writing about a hobby, don't just say "I like to read"; instead, explain what specific genre or book captivated you and why it resonates with how you see the world. If you're discussing a concept that blew your mind, focus less on explaining the concept itself and more on your reaction to it: what assumptions did it challenge, how did it shift your thinking, and why does it still excite you? Choose topics that reveal character, intellectual curiosity, and dimensions of yourself that aren't captured in test scores or transcripts.

Finally, make every sentence count. With only 250 words total, there's no room for filler or repetition. Before submitting, read your responses aloud to ensure they flow naturally and reflect your authentic voice. Caltech faculty members review the most competitive applications, so they'll appreciate genuine passion and clear thinking over polished but impersonal prose. Use this small space to be human, curious, and real.

Given the tight 150-word limit, Caltech's admissions team expects you to be direct and factual. This is not the place for narrative storytelling or emotional appeals; instead, treat this essay as an informational addendum that provides essential context the admissions committee needs to fairly evaluate your transcript. State exactly what circumstances affected your coursework (limited access to advanced STEM courses due to your school's offerings, a documented illness or family emergency, a significant disruption like a natural disaster), then briefly explain how it influenced your academics. Caltech's faculty will be reviewing your file, and they understand that students attend schools with vastly different resources.

The key distinction here is that you should only respond if you have genuinely experienced something beyond your control that impacted your academic performance or course options. Choosing to work part-time, for example, or deciding not to pursue an optional course would not qualify. Caltech explicitly states it wants to understand the full context of your application, so if your school lacked certain AP or IB courses in STEM, or if an external event disrupted your studies, explain that clearly. Be specific: name the subject areas you couldn't access, dates of disruptions, or other concrete details that help admissions officers understand what you faced.

Keep your tone humble and straightforward; avoid making excuses or over-explaining. The goal is to ensure that the admissions committee doesn't penalize you for circumstances entirely outside your control. If you have nothing significant to report, it's perfectly acceptable to skip this optional essay; forcing a response when nothing of substance occurred will only undermine your application.