When it comes to hair toning, there is no one-size-fits-all answer. The frequency with which you need to tone your hair will depend on a number of factors, including the current condition of your hair, the desired results, and how often you wash your hair. That said, here are a few general guidelines to help you determine how often to tone your hair:
If you have healthy, uncolored hair: You probably don't need to tone your hair at all! Toning is typically only necessary if you have color-treated or damaged hair.
If you have color-treated hair: Depending on the shade of toner you use, as well as how often you wash your colored locks, you may need to tone every 1-2 weeks.
If you have very damaged/bleached hair: In this case, it's best to consult with a professional stylist before using any type of toner. Over-toning can further damage already fragile strands.