With its over 6.3 million enrollments, CS50, Harvard’s Introduction to Computer Science, is one of the most popular online courses ever. And it’s one of Class Central‘s Best Online Courses of All Time.

Having taken the course myself, I (Manoel) can’t say I’m surprised. The course is excellent: it has a fantastic instructor; it offers a rich learning experience; and the course content is refreshed every year, on January 1st.

Most notably, the course is entirely free, and it includes a free certificate of completion. But understanding how to obtain it can be a bit confusing. So in this article, let’s discuss CS50 and explain how you can earn a free certificate.

• CS50 Overview
• What’s New in 2025
• Different Certificate Types
• How to Get a Free Certificate

(Harvard also offers other free courses on topics such as Python, web development, and AI. Learn more in our Harvard CS50 guide.)

CS50 Overview

CS50 is taught by Harvard Professor David J. Malan, who’s also been teaching the course on campus since 2007. Malan is a real showman. Forget dull PowerPoint presentations with monotone voice-overs. Malan takes the stage in Harvard’s beautiful Sanders Theater to enthusiastically teach computer science in front of a live audience.

It’s one of the most striking aspects of the course. It’s really well made. Malan paces the stage while filmed from multiple angles, using props to explain concepts, inviting students on stage for interactive demos, or standing at his laptop in front of a green screen for live coding sessions.

The course production values are off the charts, and Malan’s passion for teaching computer science is palpable. Naturally, this has contributed to the course’s success. Even by campus standards, CS50 stands out. With around 1,000 students enrolled every Fall, CS50 is the largest course on Harvard’s campus.

I think the main strength of the online course is that Malan treats it just like his on-campus course. The online and on-campus courses are one and the same, rather than the former being a lesser version of the latter. Both have the same lectures, same problem sets, and same final project. In terms of learning, it gets really close to the full Harvard experience.

What’s New in 2025

Another strength of CS50 is that the course is updated every year, allowing it to keep up with the latest trends in the field. More specifically, the course is recorded every Fall on campus at Harvard. Then, come January 1st, the online version is updated to use the new recordings. For instance, CS50 2025 uses the recordings made at Harvard in Fall 2024.

In my experience, annual recordings are exceptionally rare in online education. In the vast majority of cases, lectures are recorded once and reused throughout the lifespan of the course. The only other course I can think of that has annual recordings is MIT’s Introduction to Deep Learning. This seems to be a privilege restricted to a few, popular courses at rich institutions.

The annual recordings are also an opportunity for curriculum updates. In 2024, beside refreshing problems sets and centralizing practice problems, CS50 introduced an exciting new feature: an AI teaching assistant, in the form of a duck chatbot (CS50 Duck) based on GPT. And, yes, CS50.ai has returned in 2025, along with instructions on where AI can and can’t be used as you work your way through the course.

As you can tell from the course mascot above, the CS50 folks are proponents of rubber duck debugging, a technique that consists in explaining your code to a literary rubber duck. By explaining it, one can gain a better understanding of its logic, and potentially discern bugs. Well, in CS50, the duck can now reply. You can try it out here, if you’re taking the course.

Like in previous years, CS50 ends with an open-ended software project ⁠— an opportunity for students to put into practice what they’ve learned throughout the course.

Different Certificate Types

So, you think this course is for you, and you’d like to get started. Great! But before, there’s one thing worth clarifying, because it often confuses learners. CS50 is offered on four platforms, but only one offers a free certificate.

❌ These three platforms offer CS50, but they do not include a free certificate of completion:

• EdX, which is the platform most people are usually familiar with. On edX, you can audit CS50 for free. However, edX doesn’t offer a free certificate. It only offers a paid verified certificate, which costs $219.
• Harvard Extension School, which is part of Harvard’s distance education division. Through this school, CS50 doesn’t include a free certificate. Instead, students can take the course for credit and receive a formal transcript, which costs $2100–3340.
• Harvard Summer School, which is also part of Harvard’s distance education division. Though this school, CS50 doesn’t include a free certificate either. Instead, students can take the course for credit and receive a formal transcript, which costs $3850.

✔️ This platform offers CS50, and it does include a free certificate of completion:

• Harvard OCW, which is Harvard’s open online course platform. On Harvard OCW, CS50 includes a free certificate of completion, like the one below. Note that the course content is exactly same as on edX, including all the assignments. The only difference is that the free certificate doesn’t involve ID verification.

Finally, to further confuse matters, even when you take the course via Harvard OCW, you’ll be asked to create a free edX account. To be clear, this is just a logistical step that will allow you to submit your assignments. You do not need to buy the edX verified certificate.

How to Get a Free Certificate

Since its launch, CS50 has maintained a firm stance toward openness through the Harvard OCW platform. In 2025, the course remains entirely free on the platform, including its certificate of completion. Above, you can see how the free certificate looks.

To unlock the certificate, you have to:

1. Score 70% or more on all the problems sets. There are 10 problems sets, one per week.
2. Score 70% or more in the final project, in the last week.

Note that you can resubmit assignments. So if you don’t pass on the first try, no problem. You can try again.

Ready? Here’s where to get started: Harvard CS50 — Week 0: Video Lesson & Problem Set. Then, simply go week by week. Happy learning!

Original article written by Manoel. Latest version updated by Pat.