It is important to have your piano tuned at least twice a year.
Just like any other musical instrument, the piano is very sensitive to any kind of weather change, it reacts to drop or rise of humidity and temperature and as a result, it goes out of tune.
“Problem pianos and heavily played pianos should be tuned more frequently”.
The best time to get your piano tuned is when seasons change.
Don’t forget! If you skip a tuning (… or two), eventually your piano will be in need of much more than just a regular tuning. Pitch raising, and maybe even double-tuning will be necessary to bring your piano back to life, and in some cases a second double-tuning is recommended within a month to make the sound/tuning stable again.
However, if you notice that your piano is out of tune during winter or summer months – as it can happen as a result of weather change, even if your last tuning took place just recently – don’t let your piano go out of shape even more by waiting until the next planned tuning time. That might be still months away, so in this case, it will be still more economical to get three tunings a year.