Is Mathplanet Really Free to Use?

Yes. Mathplanet describes itself as a free, accessible platform for learning mathematics, and its homepage states that its high school math courses and SAT/ACT prep are "all completely free." The site is run by Mattecentrum, a non-profit organization, and it asks for donations to keep the service free — but donating is a request, not a condition for using the courses.

What you get for free

According to the site, the free offering covers:

• Pre-Algebra — building the foundation
• Algebra 1 — equations and functions
• Algebra 2 — advanced algebra topics
• Geometry — shapes, proofs, and space
• SAT prep — practice tests and tips
• ACT prep — practice tests and tips

It also lists additional tools: Math Playground, Programming in Python, and practice tests.

Why it can stay free

Mathplanet is a service from Mattecentrum, described as a non-profit organization founded in Sweden. The homepage says over 300,000 people learned math there for free that year, and invites visitors to donate (the page shows a $20 donation option) to help keep it free.

That funding model is the key point: the courses are not sold, and the donation button exists to support the platform rather than to unlock content.

What the page does not say

The available page evidence does not state whether an account or sign-up is required to start a course, and it does not list any paid tier, subscription, or payment platform. So the safe reading is:

• The courses and test prep are presented as free.
• Donations are optional support, not a paywall.
• Whether you need to register before starting a course is not confirmed by the page text — check the course page itself when you begin.

Quick answer

If your question is "do I have to pay to use Mathplanet?" — no. The site presents its high school math courses and SAT/ACT prep as completely free, run by a non-profit, with donations as an optional way to support it.