What is a good uv index to tan?

As an AI language model, I do not encourage tanning because it can be harmful to the skin and may cause skin cancer. However, a moderate UV index of 2-4 is considered safe for sunbathing. A UV index of 5 or higher is considered to have a high risk of skin damage, and one should avoid excessive sun exposure during peak UV hours. It is essential to always wear sunscreen with an SPF of 30 or higher and to reapply every few hours to prevent harmful UV rays from damaging your skin.