There is so much controversy surrounding the need to cut or not to cut. In my experience as a woman and my experience as a professional hairdresser, I believe the appropriate time to trim one's hair is based on the individual. Some factors that affect the frequency of your trim include:
1. Your hair's current state of health
2. The shears used on your cut
3. Your hair care regiment which includes (conditioning, cleansing, and styling)
4. Your use of heat
5. Good Ole' Genetics
These factors truly influence your individual need for a cut or trim. You should first discover this list of 5 factors in relation to your hair and from there decide on your personal hair goals. Are you growing your hair long? Growing your hair into a new and different shape? Are you repairing hair damage? Perhaps you simply want to maintain you current look. These questions will determine when and how to cut your hair.
Growing your hair long: When growing your hair long, you want to take some type of vitamin on a regular basis to strengthen your hair before it comes out of your head. You may trim your hair on a regular basis of 4-6 months, if your hair is in tip top shape, you use minimal to no heat, and you wear protective styles that conceal your ends most of the time.
Growing your hair into a different shape: When transitioning to a new shape, you may trim your hair between 2-3 months. Depending on the new shape, you may just trim a portion of your hair, like the front or the back. Then, 1-3 months later, come back and trim your hair again. Within that 3-6 month period you should be able to change your shape in a healthy manner.
Damage Repair: When hair is damaged, just cut it off. If for some reason you are unable to do that, then trim what you can handle parting with, and revisit the trim 2-4 weeks later. Hair grows at a rate of about 1/4-1/2 inch per month. Keep this in mind and do the math if that helps you. If parting with bad ends are not a problem for you, go ahead and cut the dead ends and then make a commitment to the health of your hair. From the fresh cut ( no more damage), revisit your trim every 2 months based on your use of heat and conditioning methods.
Maintenance: If you have a nice shape and want to keep it. Consider trimming roughly 1/4 inch of hair every 4-6 weeks. This will keep your grass mowed, trimmed and cleaned up. This is a great place to be if you love your hair and love your look. This type of maintenance will thicken your hair over time and allow up to have flexibility in styling options. This is where we all want to get to. When you get here, remember to stick to a healthy hair regiment in order to maintain your fresh do!
I've been in the maintenance category for years now. I put down the scissors a few months ago (although I picked them back up a few days ago, lol) but it's so hard to let go of my bob shape!