Not all kidney stones need to be removed. Many pass on their own, especially smaller ones. Stones under 5 mm in diameter have roughly a 76–87% chance of passing without any intervention, while stones between 5 and 7 mm still pass naturally about 60% of the time. The decision between waiting and intervening depends on the stone’s size, its location, whether it’s blocking urine flow, and how well you’re managing symptoms at home.
Size Is the Biggest Factor
The smaller the stone, the better the odds it will travel through your ureter and into your bladder on its own. Stones 1 mm across pass about 87% of the time. For stones 2 to 4 mm, the rate drops slightly to 76%. At 5 to 7 mm, you’re looking at around a 60% chance. Once a stone reaches 7 to 9 mm, the odds fall to 48%, and stones larger than 9 mm pass on their own only about 25% of the time.
These numbers mean that for most small stones, your doctor will likely suggest a period of watchful waiting rather than jumping straight to a procedure. But size alone doesn’t tell the whole story. A 4 mm stone stuck high in the ureter near the kidney has a longer, more difficult journey than one that’s already near the bladder.
How Long You Can Safely Wait
If your stone is a candidate for passing naturally, the clock still matters. A blocked ureter puts back-pressure on the kidney, and the longer that pressure lasts, the greater the risk of permanent damage. For stones in the lower ureter (closer to the bladder) under 6 mm, waiting up to about four weeks is standard. Some research suggests selected patients can safely wait up to two months for distal stones if imaging shows things aren’t getting worse.
Proximal stones, those higher up near the kidney, are trickier. Stones over 6 mm in the upper ureter generally warrant treatment within the first month rather than prolonged waiting. Throughout this observation window, your doctor will typically schedule follow-up imaging to check whether the stone is moving, the kidney is swelling, or the blockage is worsening.
Medication That Helps Stones Pass
Your doctor may prescribe an alpha-blocker, most commonly tamsulosin, to relax the smooth muscle lining your ureter and give the stone a wider path. A large meta-analysis of 49 studies found that tamsulosin raised the passage rate from about 70.5% to 80.5% and shortened the time it took for stones to come out by roughly 3.5 days. It’s well tolerated and considered safe for short-term use. You’ll typically take it alongside pain medication and plenty of fluids while waiting for the stone to pass.
One Type of Stone Can Be Dissolved
Uric acid stones are unique because they can sometimes be dissolved without any procedure at all. Uric acid crystallizes in acidic urine, so raising your urine pH to between 6.5 and 7.0 with an oral alkalinizing agent can break these stones down over time. Potassium citrate is the most commonly used option, and studies show complete dissolution rates of 50% or higher in most trials. One study using a combination citrate formula achieved an 80% complete dissolution rate.
The catch is time. Successful dissolution takes a minimum of about three months and can stretch much longer depending on stone size. You’ll need to monitor your urine pH regularly at home using test strips to make sure you’re staying in the target range. This approach only works for confirmed uric acid stones, not the more common calcium-based stones.
When a Stone Must Come Out
Certain situations make removal necessary regardless of size. The most urgent is an obstructing stone combined with signs of infection. When bacteria get trapped behind a blocked ureter, the resulting infection can escalate to urosepsis, a life-threatening condition with mortality rates between 28% and 41%. This requires emergency drainage of the kidney, not days of waiting.
Other clear triggers for intervention include:
- Persistent obstruction that isn’t resolving, which can cause the kidney to swell (hydronephrosis) and, if prolonged, lead to irreversible scarring and loss of kidney function
- Intractable pain that doesn’t respond to medication
- Stones larger than 15 mm, which have very low odds of passing
- A stone in a solitary kidney or bilateral stones blocking both sides, where any obstruction directly threatens overall kidney function
When obstruction goes untreated for too long, the sustained pressure compresses kidney tissue, thins the outer layer of the kidney, and eventually causes permanent fibrosis. In acute cases, kidney function can recover fully once the blockage is cleared. In chronic cases, the damage is irreversible even after the stone is gone.
What About Stones That Cause No Symptoms
Many kidney stones are discovered incidentally on imaging done for something else entirely. If a stone is sitting quietly inside the kidney, not blocking anything, and not causing pain or blood in the urine, active removal isn’t always necessary. Guidelines from the American Urological Association and the European Association of Urology both consider surveillance a reasonable option for asymptomatic, non-obstructing stones.
For stones under 1 cm that aren’t causing problems, most urologists favor a conservative approach with periodic imaging, typically every 6 to 12 months. For stones over 1 cm, follow-up tends to be more frequent, every 4 to 6 months, and the threshold for recommending treatment is lower. Active removal is generally recommended when a silent stone starts growing, when there are signs of obstruction or infection, or when the stone exceeds 15 mm. Your personal risk factors also play a role: people in certain occupations like pilots, frequent travelers, or those with a history of complicated stones may benefit from elective removal even without symptoms.
How Removal Procedures Compare
When a stone does need to come out, two common approaches are shock wave lithotripsy (SWL) and ureteroscopy (URS). SWL uses focused sound waves from outside the body to break a stone into smaller fragments that can then pass naturally. It’s noninvasive, but it often takes multiple sessions. After one session, the stone-free rate is only about 37%. After three sessions, it climbs to roughly 85%.
Ureteroscopy involves passing a thin scope up through the bladder and into the ureter to grab or laser the stone directly. It achieves an 82% stone-free rate in a single procedure, comparable to three rounds of SWL. For stones under 10 mm, both methods perform similarly, with URS clearing about 94% and three sessions of SWL clearing about 88%. For stones 10 mm or larger, the picture gets more complicated. SWL actually achieved higher stone-free rates (70% vs. 55%) for larger proximal stones in one comparative study, because big stones near the kidney sometimes migrate upward during ureteroscopy, leaving fragments behind.
Patient satisfaction between the two tends to be similar overall. SWL is less invasive but requires patience across multiple sessions. URS provides faster relief in a single procedure but may involve a temporary ureteral stent afterward, which can cause discomfort for a few days to weeks. Your urologist will recommend one over the other based on stone size, location, and your anatomy.