Terms of Use

Last updated October 12, 2026

Stack Days is an AI personal trainer. By making an account on the website or the iPhone app you agree to these terms. If you don't agree, don't use it.

It's not medical advice

Stack Days gives general fitness and training guidance. It isn't a doctor, physical therapist or registered dietitian, and nothing in it is medical advice, diagnosis or treatment. Exercise carries a risk of injury.

• Check with a doctor before starting a new program, especially if you have a heart condition, high blood pressure, an injury, are pregnant, or haven't exercised in a long time.
• Stop and get help if you feel chest pain, dizziness, faintness, shortness of breath beyond normal effort, or sharp or lasting pain.
• Use your own judgment about weights, intensity and whether a movement is right for you. You're responsible for how you train.

The coach is an AI

The coach is Claude, an AI model made by Anthropic. It can be wrong: it can misjudge what's right for you, get a number or a fact wrong, or link to a source that doesn't say what it claims. Treat its plans and answers as suggestions from a knowledgeable assistant, not instructions you have to follow. What you share with it is handled as described in the Privacy Policy.

Your account

• You need to be at least 13 to use Stack Days.
• Keep your password to yourself. You're responsible for what happens in your account.
• Don't misuse the service: no trying to break it, get around its daily limits, get into other people's accounts, or use the coach for things that have nothing to do with training.
• You can delete your account whenever you like in Settings. That erases everything in it.

Your content

What you write and log is yours. You give us permission to store it, process it (including sending it to Anthropic for the coach) and back it up, only to run Stack Days for you.

Free, and the fine print

Stack Days is free. There's a daily limit on coach messages so it stays up for everyone. It's a small independent project provided as is, without warranties. To the extent the law allows, we aren't liable for injuries, losses or damages from using it or from following its suggestions. We may change or shut down the service, or update these terms; if the changes are significant we'll tell you in the app.

Apple

If you use the iPhone app, these terms are between you and us, not Apple. Apple isn't responsible for the app or its content, has no obligation to provide support for it, and is a third-party beneficiary of these terms. Apple's standard Licensed Application End User License Agreement also applies, except where these terms say otherwise.

Contact

Questions or anything else: [email protected].