Is it still a kidney stone of has it passed into the ureter and is now a ureteral stone? If it is just sitting in the kidney it will probably stay there for some indeterminate time, maybe, "forever".
If in the ureter, it can cause pain and blood in the urine
as it makes it way down. The chances of stone passage for stones 5-7 mm, 60%; for stones 7-9 mm, 48%.