What are the chances of a 9.8 mm obstructive kidney stone passing on its own?

Not so great...: Chance of stone passage decreases with increasing stone size. In one report I found of 172 patients with ureteral stones, the likelihood of spontaneous stone passage was 87 percent for 1 mm stones, 76 percent of 2 to 4 mm stones, 60 percent for 5 to 7 mm stones, 48 percent for 7 to 9 mm stones, and 25 percent of stones ≥9 mm.

Very low: most likely will not pass spontaneously