In general, the laws on tinting depend on the state. For California, the front windshield and side windows can have up to a 70% tint. There is no restriction on the rear and back-side windows. The catch is if the rear window is tinted, it has to have dual side mirrors to ensure you can see.
While you could attempt to tint your windows yourself, you may want to consider reaching out to a professional. Since there is a law on tinting, a professional can ensure your windows aren’t over-tinted.
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