I change mine often, but I do change my needle according to what I am working on. If just piecing I just a 70/10, a 75/11 or an 80/12 sharp, if sewing something thick I use a 90/14 or 100/16, and when quilting or doing something with a lot of decorative stitching I use a topstitch needle. So I have a roll of the blue painters tape in a drawer of the sewing cabt and mark on it what size needle is in the machine and the date I put it in and it's stuck to my sewing machine. I know my sewing machine dealer says I should change the needle every 8 hours of sewing, but I don't. My machine will also make a noise and then I know it's time to change. My quilting buddy is great for not even knowing what size needle is in her machine. Several times when i was up at her place sewing her machine would be making that noise and I had to tell her to change her needle. She does the same thing with the blades in her rotary cutter - she has terrible cuts in the mat because of dull blades and having to press too hard. She's the first one to tell you that she is so cheap, she squeaks when she walks. She's just too funny sometimes.