In the first year, the National Piano Manufacturers Association recommends that you have your piano tuned four times. This is a period of environmental adjustment for a new instrument, and proper attention is important.
After the first year, the piano should be tuned at least twice each year, depending upon the frequency of use and atmospheric conditions.
Ideally, A piano should stay close to the standard A440 pitch from tuning to tuning, so that only relatively small "fine" adjustments need be made, resulting in a much more stable tuning.
If a piano’s tuning is too far below A440 because of long periods of neglect, a double tuning, or "pitch raise" is performed to get the tuning back up to pitch. During this process, the piano strings are first stretched to a pitch above A440 in a quicker tuning anticipating that they will settle back down to A440. The tuning is then gone over a second time to stabilize and settle the strings. This is most often done during a single visit. After that process is performed, the piano should only need continued regular tuning maintenance at least two times a year.
Your piano was tuned many times before it left the factory. It was tuned to, and should be maintained at, A440 pitch. This is the internationally accepted standard and the pitch at which the pianos are engineered to sound best at.
Unfortunately, no matter how expertly a piano is tuned, atmospheric variations and the nature of the piano's construction constantly conspire to bring it off pitch.The backbone of any maintenance program is regular tuning. These tunings should occur as needed to compensate for changes in humidity and temperature, and movement of strings from use.