Privacy Policy

This Privacy Policy explains how Calculus Master (“we”, “us”, the “Service”), operated from Taiwan and available at calculusmasterr.com, handles information about visitors and registered users. By using the Service you agree to this policy.

1. Information we collect

• Account information. When you create an account we store your email address and a display name. Passwords are never stored in plain text — they are salted and hashed (scrypt) before storage.
• Google sign-in. If you sign in with Google, we receive your email address, name, Google profile picture, and Google account identifier from Google. We do not receive your Google password.
• Learning progress. Which lessons and study-plan days you mark as complete, and which courses you have started.
• Payment information (if you subscribe). Payments are processed by Stripe. We never see or store your full card number; we store only a subscription status and a Stripe customer identifier.
• Marketing interest list. If you submit your email through a pricing or offer form, that email is recorded so we can contact you about the product.
• Usage data. Standard analytics (pages viewed, approximate location, device/browser) via Google Analytics.

2. How we use it

• To create and secure your account and keep you signed in.
• To send account emails (verification and password reset).
• To save and display your learning progress across devices.
• To process and manage subscriptions, if you choose to buy one.
• To understand how the site is used and improve the lessons.

We do not sell your personal information, and we do not use your data for advertising.

3. Service providers

We share data only with the providers needed to run the Service:

• MongoDB Atlas — database hosting for accounts and progress.
• Zeabur — application hosting.
• Google — OAuth sign-in and Google Analytics.
• Resend — sending verification and password-reset emails.
• Stripe — payment processing (only if you subscribe).

4. Cookies

We use a strictly necessary, HTTP-only session cookie to keep you signed in. We also load Google Analytics, which sets its own cookies. We do not use advertising or cross-site tracking cookies.

5. Data retention

We keep your account data for as long as your account exists. If you ask us to delete your account, we remove your account record, credentials, and learning progress, except where we must keep limited records for legal or accounting reasons (for example, past payments).

6. Your choices

You can view and update your email and name from your account page, and cancel a subscription at any time through the billing portal. To request a copy of your data or deletion of your account, email us at the address below.

7. Children

The Service is intended for high-school and college students and is not directed to children under 13. If you believe a child under 13 has given us personal information, contact us and we will delete it.

8. Changes

We may update this policy from time to time. Material changes will be reflected by a new “Last updated” date at the top of this page.

9. Contact

Questions about this policy or your data: calculus.masterr@gmail.com