How to Prepare for a Coding Interview: Free Resources (2026)

Most technical interviews at the junior-to-mid level test three things: data structures and algorithms, basic problem solving, and one behavioral round. You do not need a paid bootcamp or a LeetCode Premium subscription to get ready for that. The four things you actually need are a solid DSA foundation, regular problem-solving practice, two or three real projects on GitHub, and a habit of talking through behavioral answers. Give yourself those four and the rest is optional. This guide walks through what interviews test, which free resources actually teach it, where to practice for free, and a concrete 6-week plan you can start today. It is honest about the limits too: free prep gets most people to a junior or early-mid offer at companies that are not Google or Meta. For FAANG senior loops, you will need more time and a few things that are hard to get for free. We will flag those as we go. If you are still deciding whether a degree matters for the job hunt at all, read /guides/how-to-get-a-coding-job-without-a-degree alongside this.

Be clear-eyed about what you are preparing for. At most companies, the technical rounds break down like this. Algorithms and data structures are the core: arrays, hashmaps, strings, linked lists, stacks, queues, trees, graphs, sorting, searching, and some dynamic programming. This is 60 to 70 percent of what gets tested at companies that run a coding round. If you only have time for one thing, it is this. CS fundamentals sit underneath: Big-O notation so you can talk about how fast your solution runs, recursion, and a working sense of how memory and computation behave. You do not need a full degree here, but you need the vocabulary. System design shows up for mid and senior roles. If you are targeting your first job, you can skip it for now and come back later. Behavioral rounds are real interviews, not a formality. Expect STAR-format questions (Situation, Task, Action, Result) about how you have worked, handled conflict, or shipped something. Prep three or four stories in advance. One honest note on scope. FAANG-style loops run two or three DSA rounds plus behavioral and, for senior roles, system design. Most startups and mid-size companies lean on take-home projects or a walk-through of your existing work instead. This guide targets the common case: junior to mid, not a FAANG senior loop. If you are aiming higher, the same resources apply; you just need more months.

You have to learn the material before you can practice it. These are the free resources we would actually recommend, with a one-line limitation for each so you pick the right one. freeCodeCamp JavaScript Algorithms and Data Structures covers arrays, stacks, queues, linked lists, trees, graphs, and dynamic programming, with a free verified certificate at the end. It runs in the browser, so there is no setup. About 300 hours, self-paced. Best for JavaScript learners at the beginner-to-intermediate level. Limitation: it teaches the concepts well but gives you little interview-style practice, so pair it with a practice platform. See /platforms/freecodecamp for the full track, or our ranking of free JS courses at /guides/best-free-javascript-course-2026. CS50x (Harvard, free via edX) is the clearest introduction to how computers actually work: computation, Big-O, sorting, memory, and recursion, taught across several languages. If algorithms feel like magic right now, this is the course that fixes that. Best for true beginners who want a strong foundation before they start grinding problems. Limitation: it is a broad CS course, not an interview cram, so you will study things (like C and memory) that are not directly tested. See /courses/cs50-intro-computer-science. Khan Academy's free algorithms unit gives visual, animated explanations of sorting and searching. It is a good supplement, not a full course. Best for visual learners who need a light primer before a heavier resource. Limitation: it stops well short of the trees, graphs, and dynamic programming that interviews lean on. MIT OpenCourseWare 6.006, Introduction to Algorithms, is the rigorous option, with real lectures and problem sets. It is overkill for most junior candidates, but excellent if you want to genuinely understand the theory. Best for CS graduates or anyone targeting research-heavy or top-tier roles. Limitation: it assumes you already know Big-O and can write clean code, so it is not a starting point. See /courses/mit-ocw-algorithms-python. For a wider reading list on this, our full ranking is at /guides/best-free-data-structures-and-algorithms-courses-2026.

Learning the concepts is one skill; solving problems under time pressure is a different one. You need both, and the second only comes from reps. Here is what is genuinely free, with honest limits. LeetCode's free tier gives you more than 150 problems, which is plenty to start. Work Easy problems first, then move to Medium, which is the difficulty most interviews target. The community-compiled "Blind 75" list is a widely used free starting set that covers the common patterns. Limitation: without Premium you do not get company-specific question lists or the built-in solutions for every problem, but you do not need those at the junior level. Exercism offers language-specific problem sets with optional feedback from volunteer mentors, and it is fully free. It covers Python, JavaScript, Go, and more. It is less about interview speed and more about writing clean, readable code, which is a habit that pays off in take-home rounds. Limitation: mentor feedback can take a while, so do not treat it as your only timeline. HackerRank is good for absolute beginners working through arrays, strings, and recursion. It gets repetitive fast, so use it as a warm-up rather than your main platform. These platforms pair naturally with the courses above. Once you have the foundation from freeCodeCamp or CS50x, the courses in our /guides/best-free-data-structures-and-algorithms-courses-2026 ranking plus steady LeetCode reps are the combination that actually moves the needle.

Here is one concrete path, not a menu. Follow it in order. This assumes one to two hours a day and that you already know at least one language a little. Pick Python or JavaScript for most roles. Weeks 1 to 2: build the foundation. Work through freeCodeCamp's Algorithms certification or CS50x through the algorithms sections. The goal by the end of week 2 is a working grip on Big-O, recursion, arrays, and hashmaps. Do not rush to LeetCode yet; you will just get discouraged solving problems whose underlying ideas you have not learned. Week 3: arrays and strings on LeetCode's free tier. Aim for 20 Easy problems. For each one, write out your approach in plain words before you touch code, then implement it. This one habit, plan first, code second, is what interviewers are actually watching for. Week 4: trees, linked lists, stacks, and queues. Aim for 15 problems, Easy moving into Medium. Focus on recognizing the pattern rather than memorizing any single solution. When two problems feel similar, name why. Week 5: one dynamic programming module from freeCodeCamp, plus 10 Medium problems. Start solving out loud, narrating your thinking as you go. In a real interview, your commentary matters as much as your final answer, and it is a skill you have to rehearse. Week 6: get interview-ready outside of algorithms. Make sure two projects are on GitHub with clear READMEs; /guides/how-to-build-a-developer-portfolio covers how to present them so they get replies. Write three behavioral stories in STAR format. Then do two mock interviews. Pramp is free and pairs you with another candidate so you each practice both sides. Honest caveat: this is a junior-to-mid prep plan, not a FAANG senior plan. For a top-tier senior loop, plan on three to six months minimum and roughly double the problem count.

The Content Quality Standard we hold ourselves to means being straight about the gaps, so here they are. Structured feedback on your code is limited when you practice solo. You can catch whether an answer is correct, but a mentor who tells you your approach was fine yet your communication was muddy is harder to replace for free. Exercism's volunteer mentors and mock-interview partners on Pramp help, but it is not the same as a paid coach. System design prep for senior roles is the weakest area for free resources. There are good free talks and articles, but the structured, feedback-driven prep that senior loops reward mostly lives behind paywalls. If you are targeting mid or senior, budget for this being harder. Mock interview practice is possible for free but takes initiative. You have to schedule sessions on Pramp, find a peer group, or trade practice rounds with someone else who is job hunting. Nobody hands it to you. And a scope limit: machine learning and data engineering interviews are SQL-heavy and case-study heavy rather than algorithm heavy, so this guide does not cover them. If that is your target, start with /guides/best-free-data-science-courses-2026 instead.

Start with CS50x if you have never touched algorithms and want to understand what is going on under the hood, or freeCodeCamp's Algorithms certification if you already write JavaScript and want to move faster. Either way, move to LeetCode's Easy problems after about two weeks and do not stop the daily reps. The 6-week plan above is enough for most junior and early-mid roles at companies that are not FAANG. For a top-tier senior loop, double the timeline and add system design. The bigger point: do not buy anything until you have actually worked through the free options. Most people never need to. The paid tools sell convenience and structure, not secret knowledge, and the knowledge is all free if you are willing to be your own project manager for six weeks. When you are ready to run the search itself, /guides/how-to-get-a-coding-job-without-a-degree covers how hiring actually works when your proof is projects instead of a diploma.