Use a magnifier to inspect the point. You'll be able to see any nicks or flattened areas.

Same here.

I replace a needle everytime I start a new project.

Every Monday...I know that's weird but it keeps me changing them.

If it drags or pulls on fabric or breaks then I change. I do not change my needle as often as I have seen others do here and have had no problems. I sew over pins and don't have much of a problem with breaking the needles. I sew on the average of 3 to 5 hours per day. Personal choice I think.
Have a Blessed day
Ellen

That is the standard answer. I never think about it until after I have started a project, all threaded up and am already sewing. So, I guess the answer to your question from me is every couple of projects (not often enough). Also I can "hear" the difference when the needle is not sharp - it does not pierce the fabric and glide through smoothly but "makes a noise" when it hits the fabric.

That's what I was thinking. I only change it if I need to.

I change mine after about 15 hours of sewing.

Mostly I can tell by the sound, feel of the machine. I also make it a "point" :wink: to clean/oil machine at that time if necessary

Generally every 8 hours of working is the rule of thumb. However, whenever you hear a popping sound when the needle goes in - it is definitely time as you have left it too late. One gets used to "knowing" when it is time - don't wait until the needle breaks to do it.