This is a question that I receive quite often. Most hairdressers would say "6 weeks". I however, think it depends on a lot of different factors. Clearly, this my own opinion AND this is for my clients that should be on some sort of personalized regimen, and keeping their hair healthy. (AKA moisture masks, olaplex or smartbond, using heat protectants)
IF you are a guy and/or a girl who keeps their hair CLIPPER short: you are going to want to come in 3-4 weeks to maintain your look.
IF you have a short to medium length haircut and you want to maintain the length of that cut & keep the shape fresh: 6-8 weeks is perfect for you.
IF you have long (DAMAGED/FINE) hair with or without layers: 8-10 weeks + a conditioning or strengthening treatment.
IF you have long (HEALTHY/THICK) hair with or without layers: then you can go about 10-12 weeks.
IF your hair is decently healthy + you are growing it out from another style or just want long hair: 12 weeks + get a conditioning treatment.
NOW, this all varies person to person: this is just a guide. However, I never suggest going longer than 12 weeks without a trim. That is THREE MONTHS, people. If you have trouble remembering to get a haircut, the best option for you is prebooking your appointments. You can book them online or through me. By having your appointment set for you, you are more likely to take care of your beautiful hair! And as usual, if you have any questions- let me know!