Ah, the age old question. One which requires a multi-part answer.
Don't make the mistake of thinking just because you have long hair or you're growing it out that it means that you don't have to get regular trims. Because you do. In fact, it might be more important for you than for someone with shorter hair.
Your ends can become dry and brittle, which leads to breakage. So to keep your hair in tip-top shape, book your appointments every 8-10 weeks.
You have a little more wiggle room with your haircut schedule. But even still, you need to make regular appointments to the salon to keep your locks looking nice. Go visit your stylist every 6-10 weeks.
Because your hair is so short, it probably has a defined shape to it. Meaning, you need to keep that shape unless you want to look like someone who hasn't had a haircut in a while. It's super important to make your appointments every 4-6 weeks. Unless you're trying to grow it out. Then you can go a bit longer. But definitely no more than 8 weeks.
How often do you get your hair cut? Do you follow the "norm" schedule, or make your own rules?