Many kidney stones will pass spontaneously and will not require surgical treatment. Whether a stone can pass successfully primarily depends on the size of the stone. Based on several studies of stone patients, a size criteria of 5mm or less (about 0.2 inches) is generally felt to predict a reasonable chance (50-70%) for spontaneous passage.
The location of a kidney stone when it is diagnosed also is predictive of likely success at spontaneous passage. Stones that are more distal (closer to the bladder) are more likely to pass than stones that are more proximal (closer to the kidneys).
The decision to allow a stone to pass spontaneously will also take in account the amount of pain you are experiencing, your medical health, the possibility of infection, and other factors. Typically, a period of 4-6 weeks is allowed to give stones a chance to pass.
Medications to help pass kidney stones are now more commonly being given to patients experiencing an active stone episode. These medications can improve the chances of successful passage of a stone, decrease the pain associated with a stone episode, and decrease the time required for passage.