I change my blades when it does not cut all the way thru my strip of fabric. Sometimes they last a very long time and then again, they only last a short time. However one thing that helps them to last longer is a good board. I treat myself to a new cutting board every year. What a difference that makes. Because if you board has been used a lot and has grooves in it or dried out a little it will dull you blade. Marge