If your hair is healthy trim every 4th month which equals 3 times a year. This is enough to keep your hair healthy but still maintain length.
Every 6-8 months or whenever you feel that a trim is needed
i just trim whenever i feel like my ends look rough. everybody is unique so it's all up to you. a lot of people cut their hair religiously for no good reason lol
You really dont need to if your hair is healthy. But if you regularly get split ends due to heat styling, every 4 to 6 months. If you want to obtain a certain length, 8. But honestly and personally, if my hair isn't breaking off, i wont cut it regardless of split ends.