Ideally a piano needs to be tuned at least 2-3 times a year to keep the piano well maintained. But a lot depends on how often you play.
For example, if you only play once or twice a week, then you may get away with just twice a year. If you play quite frequently, then you should get the piano tuned about 3-4 times per year.
The very bare minimum is once per year, but this is only if the piano hardly gets played. I certainly wouldn’t advise this though.
Why does a piano need to be tuned?
A piano is a string instrument, and the strings are stretched so tightly that the tension will drop over time whether you play it or not. What a lot of people also don’t realise is that the strings may all drop at a similar rate, meaning that the piano still may sound in tune overall; until you compare with to a piano that is correctly tuned to the standard pitch.
So if a piano is left for too long without being tuned, it may not be able to take the stress of the string tension being increased back up to the standard pitch. It’s possible that a string may break which could prove very expensive to replace.
Does humidity affect the piano?
Yes, and this is also a very good reason to have the piano tuned. Pianos are approximately 85% wood, and so are affected by humidity. Because of this, some people may decide to have the piano tuned at the start of each season, which isn’t a bad rule to follow in my opinion. Other people may argue that it doesn’t really matter when you tune the piano, as the change in climate is very gradual throughout the year. This is true, but if you made the decision to tune the piano at the start of each season, it allows you to stick to a time table so you don’t forget. And tuning the piano 4 times a year is a sure fire way of keeping the piano in great condition.
A piano can easily last a hundred years if it’s tuned regularly and looked after properly, and pianos don’t depreciate in value like most things do. So although pianos can be expensive, and having them tuned more often is also an additional cost; try to remember that the piano can last a whole lifetime, so is a great investment!