Version 2.0.0 · effective 12 September 2026 · earlier versions
This box is a summary. The full terms below are the agreement, and if the two differ the full text wins.
Erudia is operated by an individual based in Chicago, Illinois, United States. The operating entity and its postal address will be named here when it is formed. Until then, "Erudia", "we" and "us" mean that individual, and legal notices go to erudia@erudia.org.
"You" means the person using Erudia. If you create an account for someone else, such as a child or a student, you accept these terms on their behalf and you are responsible for their use.
You must be at least 13 years old to hold an account. We ask your birth month and year before you can create one, and we rely on your answer. If you are between 13 and 18, some engagement features are off by default and you can turn them on in Settings; see the Children's Privacy Notice for what happens for a learner under 13.
You accept these terms by ticking the box that says so when you create an account or subscribe, or by ticking the box at the age screen if you learn as a guest. We keep a record of the version you accepted and when. Nothing here claims that browsing the site alone forms a contract.
We may change these terms. For a change that affects your rights or obligations (a price, how we use data, the dispute section, the licence you give us), we will tell you by email and in the app at least 30 days before it takes effect, show you what changed, and ask you to accept again. You may decline: your account continues under the terms you accepted until your next renewal, after which you can cancel. A change never applies to a dispute either of us has already given notice of. For other changes (wording, addresses, typos) we update the version line at the top and note it in the app.
Erudia provides interactive mathematics lessons in 87 subjects, a spaced-repetition review system, practice generators, printable worksheets and books, competition-style problems, duels and leaderboards, and a community where learners share problems. We add, change and sometimes remove features. If we remove a feature that was part of a Premium subscription, you may cancel and we refund the unused part of any period you prepaid.
The free tier is 1,673 of the 2,815 lessons plus placement, reviews and the knowledge map. We have no plan to charge for them. If that ever changed, section 2 would apply and nothing you had already learned would be locked away from you.
You give us an email address you control and you keep your password to yourself. You are responsible for what happens under your account until you tell us it has been compromised, and then we are responsible for helping you secure it. One person, one account; do not share, sell or transfer it. You may use Erudia as a guest without an account; guest progress lives on your device only and is lost if you clear your browser.
The Acceptable Use Policy is part of these terms. In short: use Erudia to learn, do not attack it, scrape it, cheat its leaderboards or post anything unlawful or hurtful, and do not misstate your age. If you break it we may remove content, suspend or end your access; where we can, we warn you first and tell you why, and you may ask us to reconsider by email.
Premium costs $7.99 per month, or $63.92 per year ($5.33 a month, billed once), in USD. Prices are shown exclusive of tax. Any sales tax, VAT or similar tax is calculated, collected and remitted by Stripe as merchant of record and is added to your total at checkout.
Stripe is the merchant of record: it sells the subscription to you, processes the payment, holds your card details, issues your receipt and remits any tax. We never see your full card number. Erudia provides the service itself.
These are the renewal terms, which are also shown before you pay:
You cancel from Settings → Manage subscription: 2 clicks, online, in the same place you subscribed, with no offer placed between you and the cancel button. Cancellation takes effect at the end of the period you have paid for and you keep Premium until then. Before an annual plan renews we email you at least 30 days ahead with the amount and a cancel link, and we send every subscriber a reminder at least once a year. We give 30 days' notice of a price change, which applies only to renewals after that date; you can cancel before it takes effect.
Refunds, the 14-day withdrawal right, and the rights that apply where you live are in the Subscriptions, Cancellation and Refunds page, which is part of these terms.
You keep ownership of what you post. You give Erudia a non-exclusive, royalty-free, worldwide licence to host, display, format for accessibility and different screens, and include it in problem sets, and to let the providers that run the service do those things for us. The licence ends when you delete the content or your account, with one exception: a problem that other learners are already practising stays in their set, with your name removed. We do not use your name or content in advertising without your written permission, and we do not sell it.
You are responsible for what you post: you must have the right to share it, and you must not post material copied from a source you do not have permission to reproduce, including competition problems. The Community and Copyright Policy is part of these terms and has the notice and counter-notice process, the repeat-infringer rule, and the moderation rules. We may decline, edit or remove community content and we are not obliged to keep hosting it.
The Erudia name, the lessons, the curriculum, the problem generators, the software and the design are ours, protected by copyright and trademark law to the extent the law protects them. Some lesson text was drafted with the help of AI tools and then selected, arranged, edited and sequenced by a person; we claim the human authorship in that work and no more. You get a personal, non-transferable licence to use the service to learn. Printing a worksheet or a book for your own study or for a class you teach is fine; republishing the curriculum is not. Third-party libraries we ship are listed with their licences at Third-Party Licences.
Erudia is an educational tool provided as it is and as it is available. Lessons, worked solutions and generated problems can contain errors; check anything you rely on for an exam or a submission. We do not promise a learning outcome, uninterrupted operation, or that the service will meet your particular needs. Some chapters cover financial, actuarial and statistical mathematics and the service includes market and probability simulations; they are teaching tools, and nothing in Erudia is financial, investment, tax, legal, medical or other professional advice.
We back up your progress and sync it on a best-effort basis. Export it from Settings if it matters to you, because we cannot promise it against loss. We run experiments on parts of the learning engine (see the Privacy Policy) and ship features that are new.
To the extent the law allows, we disclaim implied warranties of merchantability, fitness for a particular purpose, title and non-infringement. Where you live, the law may give you guarantees that cannot be excluded, such as the consumer guarantees under the Australian Consumer Law, the digital-content rights under the UK Consumer Rights Act 2015, and the conformity rights under the EU Digital Content Directive; nothing in this section takes those away.
To the extent the law allows, neither Erudia nor anyone operating it is liable for indirect, incidental, special, consequential, exemplary or punitive damages, or for lost profits, data or goodwill, however caused. Our total liability for all claims relating to the service is limited to the greater of what you paid us in the 12 months before the claim arose or US$100. These limits do not apply to liability that the law does not allow to be limited, including liability for death or personal injury caused by negligence, for fraud, or under a consumer-protection statute that forbids the limit, and they do not limit a remedy the arbitration section gives you.
If a third party brings a claim against Erudia because of content you posted, your breach of these terms, or your violation of someone's rights, you agree to cover the loss and reasonable legal costs that result, provided we tell you promptly, let you take part in the defence, and do not settle in a way that puts an obligation on you without your consent. This section does not apply to a claim that arises from our own breach or negligence.
This section applies to any dispute between you and Erudia arising out of the service, your subscription, or these terms. It does not reach anything else.
First, we talk. Before either of us starts a proceeding, the one with the complaint sends the other a written notice of dispute (to erudia@erudia.org, or to the email on your account) with a name, the account email, what happened and what would resolve it. We then have 60 days to work it out in good faith. Time limits pause during those days.
Then, individual arbitration. If that fails, the dispute is resolved by binding arbitration under the American Arbitration Association's Consumer Arbitration Rules and its Consumer Due Process Protocol (https://www.adr.org), before one arbitrator, who decides everything including whether this section applies. The Federal Arbitration Act governs this agreement to arbitrate.
What it costs you. For a claim under US$10,000, Erudia pays all filing, administrative and arbitrator fees, unless the arbitrator finds the claim frivolous. For larger claims the AAA fee schedule applies, which caps your filing fee at US$225. Nothing in this section limits the remedies, damages, attorney's fees or statutory rights a court could give you, and neither of us owes the other confidentiality about the dispute.
Where and how. In your county, or by phone, video or written submissions if you prefer for a claim under US$10,000.
Small claims. Either of us may instead bring an individual claim in small-claims court (in Illinois, up to US$10,000).
Individual claims only. Claims are brought and resolved one person at a time. Neither of us may bring or take part in a class, collective, consolidated or representative proceeding against the other, and the arbitrator may not consolidate claims or award relief to anyone who is not a party. If the law requires that a claim proceed on a representative basis, that claim goes to court and stays there while the individual claims are arbitrated. Nothing here stops you from seeking public injunctive relief where the law gives you that right.
If many people file at once. If 25 or more demands with common issues are filed by the same or coordinated counsel, the AAA's Mass Arbitration Supplementary Rules apply and cases proceed in batches of up to 25, each batch to be decided within 120 days of the arbitrator's appointment. Time limits are paused from the first filing for everyone waiting. If a batch is not decided within that deadline, or your case has not started within 365 days of your filing, you may take your claim to court instead.
Opting out. You can reject this arbitration agreement by emailing erudia@erudia.org with your account email and the words "opt out of arbitration" within 30 days of first accepting these terms, or by using the form in Settings. Opting out changes nothing else about your account, and it holds for future versions of this section.
Governing law and courts. These terms are governed by the laws of the State of Illinois, United States, without regard to its conflict-of-law rules. Any claim that goes to court, including small claims and a claim by someone who opted out, is brought in the state and federal courts located in Cook County, Illinois, and each of us consents to that jurisdiction. If the arbitration agreement is found unenforceable, then to the extent the law allows, you and Erudia each waive a jury trial.
If you are a consumer elsewhere. If the law where you live gives you the right to bring a claim in your own courts, forbids a pre-dispute arbitration agreement, or gives you rights this section would take away, that law applies and the parts of this section that conflict with it do not bind you.
Time limit. A claim must be started within 2 years after it arises, unless the law gives a longer period that cannot be shortened by agreement.
This section survives the end of your account and of these terms.
You can delete your account at any time from Settings; that erases your data as the Privacy Policy describes. We may suspend or end an account that breaks these terms, and we will say why unless the law prevents it. If we end an account for a breach, unused subscription time is not refunded. If we close Erudia, we give reasonable notice and refund the unused part of any prepaid period.