Inflatable PFD
We do not know what you mean by "PFD", please do not use abbreviations. But the answer would be when the instructions for the "PFD" say it needs to be replaced.
Every time it is worn!
Boating regulations vary from state to state, so it is important to check the regulations within the state that you are boating. Many states allow you to have PFDs accessible but not worn when boating, kayaking and/or canoeing. Most Inflatable PFDs are US Coast Guard approved - the same as non-inflatables. Therefore, you will probably only hear that you have to wear/not wear USCG approved vests. However, most boating deaths can be attributed to the boater, kayaker, etc. not wearing their PFD/Life Vest. Inflatable PFDs are designed to be lightweight and convenient to wear - that is to encourage you to wear the vest at all times. It is extremely difficult to put on a PFD when you are already in the water, if in fact, you can access - get to your vest - once you have already entered the water. Inflatable PFDs are now coming in attractive colors, to also encourage you to wear them.
a pfd for everyone aboard
A PFD for everyone aboard
a PFD for everyone aboard
a pfd for everyone aboard
According to the manufacturers instructions.
Wearing an inflatable PFD while on a personal watercraft.
Life Jacket or PFD for everyone on board
Washing your PFD with soap and cold water could cause it to wear out.