When Should I Tune My Piano?
You should tune your piano at least once a year.
The main reason a piano goes out of tune is from temperature and humidity changes during the year. Higher humidity causes the wood to expand and dryer air makes the wood contract.
If the piano is played frequently and with force, that can make the piano gradually lose its tuning.
People who play often and have a discriminating ear will often tune every 6 months. In recording studio situations, the piano is usually tuned before each session.