CS50's Introduction to Computer Science
CS50x is Harvard's introductory computer science course, published free online: C, then Python, SQL and web programming, ending with a final project you design yourself.
Score 70% on every problem set and on the project, and the gradebook lets you download a CS50 Certificate without charge. Paying edX turns identical work into a verified HarvardX certificate instead.
Certificate facts
- Level
- Foundational
- Field
- Development & DevOps
- Access
- Free
- Assessment
- Graded projects
- Languages
- EnglishCourse materials and problem sets are in English; CS50 has dubbed the lectures into Portuguese and Spanish
- Price
- Free (read 26 September 2026)
- Validity
- never expires
- Exam delivery
- No exam: problem sets and a final project are submitted online and scored automatically in CS50's gradebook; the optional verified certificate is issued by HarvardX through edX
Prerequisites: None. CS50 recommends checking its course map first and suggests the course suits learners from about age twelve; edX and GitHub accounts are required to submit work
Renewal: None stated by CS50 or edX. The practical deadline is the course year: work must be passed by 30 June 2027 (end of day UTC) to count for the current edition, and progress only carries forward under CS50's published year rules
Source: certificate page at Harvard University · Price: The course and the CS50 Certificate are free; edX registration is required but its audit option costs nothing. The optional edX verified certificate is paid (see cost of ownership)
How to prepare
1. The vendor's free learning path
Harvard University publishes the exam objectives and a learning path free of charge — the authoritative source for scope and weighting. Open the learning path (opens in a new tab)
2. The programme
The certificate is earned inside this programme. Its facts, price and the provider's own page are on the course page; the link there carries no commission.
Affiliate disclosure: the course link above is an affiliate link — buying through them may earn us a commission at no extra cost to you. The vendor's learning path and booking links carry no commission.
One piece of work, two certificates
The requirement is identical for both documents: submit all ten problem sets and the final project, and score at least 70 per cent on each. What differs is who issues the paper. The CS50 Certificate comes from the course itself, is free, and appears as a download link in your gradebook a few hours after your last passing score. The edX verified certificate comes from HarvardX through edX, requires payment and identity verification, and can take up to a month to be issued because CS50 sends edX a list of finishers every three weeks. You can hold both. You can also pay for verification after finishing, up to ten days before the course deadline, though CS50 advises doing it earlier to avoid delays.
| Aspect | CS50 Certificate | edX verified certificate |
|---|---|---|
| Issued by | CS50 at Harvard | HarvardX through edX |
| Cost | Free | Paid, see cost of ownership |
| Identity check | None; you type the name yourself | edX identity verification |
| Timing | Within hours of completion | Up to about 30 days |
| Academic credit route | None | Can support an ACE credit recommendation |
Neither is an accredited academic qualification, and CS50 says so plainly. The verified certificate matters in one specific case: CS50x appears in the American Council on Education's guide, so a university that honours ACE recommendations may grant credit for it, but only with the edX certificate. If you do not need credit or a document with an identity check behind it, the free one is enough.
How the work is graded
There is no exam of any kind. Each problem is scored by two programs: one runs your code against checks for correctness, the other rates its style, and the two combine three to one. You can resubmit as often as you like, and only the latest attempt counts. The final project is different in kind, since you choose what to build and in which language, but it is marked against a written specification, and CS50's own FAQ names thin documentation as a common reason projects fail. Academic honesty rules apply throughout.
- Weeks: eleven weeks of material, from Scratch in week zero through C, arrays, algorithms, memory and data structures, then Python, SQL, web basics and Flask.
- Effort: CS50 suggests ten to twenty hours for each week's problem sets alone, on top of lectures; edX describes the course as twelve weeks at six to eighteen hours a week.
- Pace: self-paced, with no per-assignment deadlines, only the course year's closing date.
The gradebook resets with the course year
CS50x is republished each year. Work passed in the current edition carries forward if the course is extended, but CS50 states that work from older editions eventually stops counting and a new edition's problem sets must then be done. If you start now, aim to finish by the June 2027 deadline and download your free certificate before it passes.
Some early problem sets come in two versions, one for learners with little experience and a harder one for those with more. Either counts, you gain nothing extra for the harder one, and CS50 openly encourages switching down rather than giving up. That design choice goes a long way to explaining why so many people with no background finish the course.
What a question looks like
Written by us in the exam's style. It is not a real question from any question bank, and we do not publish those.
Your program reads words from a dictionary file into a hash table and then checks a text for misspellings. It is correct but slow on large texts. The style checker is happy, and the correctness checks pass. What single change to the data structure is most likely to speed up lookups without affecting correctness?
There is no multiple choice in CS50x; you write the program and the checks judge it. The hard part is not getting it working but reasoning about why it is slow, which means thinking about how many buckets there are and how evenly the hash function spreads words among them.
What it costs to get and to keep
| Item | Amount | Note |
|---|---|---|
| Course and CS50 Certificate | 0 USD | free; edX registration via the audit option costs nothing (read 26 September 2026) |
| edX verified certificate (optional) | 219 USD | verified seat price on the edX course page; edX was running a time-limited 30% discount code until 30 September 2026; price shown may vary by region (read 26 September 2026) |
| Renewal | not published | none; neither certificate states an expiry (read 26 September 2026) |
How much preparation, from where you are
- Never programmed
- CS50 says two thirds of its students arrive without any computer science background. Expect weeks three to five, algorithms, memory and data structures in C, to be the hardest stretch; the easier problem variants are there for exactly this reader.
- Self-taught web developer
- The later weeks will feel familiar. The value is in the C weeks, which explain what your higher-level languages hide from you.
- Computer science graduate
- No credential value. Watch individual lectures if you teach or mentor beginners.
What passing this does not prove
- Anything under exam conditions; there is no timed or supervised assessment.
- Your identity, for the free certificate: you type the name that appears on it.
- Working on a large existing codebase or with a team, beyond an optional small group for the final project.
- Depth in any one language or framework; breadth is the point.
Against the alternatives
- Responsive Web Design Certification
- freeCodeCamp's HTML and CSS certificate is narrower and more practical: it teaches you to build pages. CS50x teaches how computers and programs work, and touches the web only near the end. For a career changer who wants to understand programming rather than a single craft, CS50x is the better first course; for someone who wants to build websites soon, start with freeCodeCamp.
CS50's Introduction to Computer Science — quick answers
Is the CS50 certificate free?
Yes. Complete every problem set and the final project with at least 70 per cent each and you can download the CS50 Certificate at no cost. Only the optional edX verified certificate is paid.
Which certificate should I get?
The free one, unless you need a document backed by identity verification or want to pursue academic credit through an ACE recommendation. Both require exactly the same work.
Is there a final exam?
No. CS50x has no summative test. The problem sets and the final project are the whole assessment.
What happens if I do not finish by the deadline?
Work passed in the current edition carries forward if the course is extended, under rules CS50 publishes in its FAQ. Older work eventually stops counting when a new edition changes the problem sets, so plan to finish within the course year.
Is it a Harvard qualification?
No. CS50 describes both certificates as non-accredited, offered for self-education and vocational purposes. The on-campus course and Harvard Extension offer the accredited routes.
Where this certificate sits in the field
What comes next
Concepts this certificate draws on
Glossary entries with the reason each one matters for CS50's Introduction to Computer Science.
Last reviewed 26 September 2026 · Getting Digital