I change my needles as soon as I see any "problems" with the way they are working or start hearing the "clunking" noise. I buy them from www.cleanersupply.com. They are $1.75 for pack of 10 and shipping is between $3-4 so I stock up and buy 10 packs at a time. At only 21 cents/needle (including shipping costs) I can replace frequently without concern about money.