Please note that there is a difference between a Cut, Trim, and Dusting off your ends.
How to Retain Length
Remember no oil or shampoo or conditioner makes your hair grow. Our hair biological grows 1/4-1/2 inch a month depending on genetics.
You have to focus on the oldest parts of your hair (your ends and have a steady hair routines to gain hair retention.
That means regular trims. Some people hair require trims as early at 8 weeks while others can go 12 weeks. If you want to maintain the same length hair then trims every 6 weeks is what you would need.
Shampoo and deep condition hair weekly (this offer the best results). For those who can't commit to a weekly regime make sure not to go past two weeks of this routine.
Do not over do your hair with protein. Too much protein will harden your hair causing shedding. For those needing a protein treatment, do not use more than once in a 30 day timeframe.
Cut
when hair is damaged and very uneven or transitioning and need fresh start
Trim
ends that might be splitting or damaged or dead.
Dust
cleaning up when the hair grows uneven.