This is a matter of personal taste. There are two extremes. Some people never have their pianos tuned, believing themselves to be tone deaf (which is a myth). Pianos used for concerts are usually tuned before each concert, and often during the interval as well. Most domestic pianos require tuning every six months. This is not because they suddenly go out of tune at the six month mark, but because they are gradually going out of tune all the time, and six months is about the point at which most people notice they sound “off”.