Most small bladder stones can pass on their own with enough fluid intake, light movement, and time. Stones smaller than 4 millimeters have roughly an 80% chance of passing without intervention, while stones 6 millimeters or larger rarely pass naturally. The key variables are size, hydration, and patience, though some medications can improve your odds.
It’s worth noting that much of the clinical research on stone passage focuses on ureteral stones (stones traveling from the kidney to the bladder), since that’s where most stones get stuck. Once a stone reaches the bladder, it still needs to exit through the urethra, and the same general principles apply: smaller stones pass more easily, and fluid intake is the single most important thing you can control.
Size Determines Whether a Stone Can Pass
Stone width is the strongest predictor of whether you’ll pass it naturally. A large European Radiology study tracked spontaneous passage rates over 20 weeks and found a clear cutoff. Stones 3 millimeters or smaller passed 98% of the time. At 4 millimeters, the rate dropped to 81%. At 5 millimeters, 65%. At 6 millimeters, only 33% passed, and stones 6.5 millimeters or larger had just a 9% passage rate.
If your doctor has measured your stone on imaging and it’s under 5 millimeters, the odds are in your favor. Between 5 and 6 millimeters, it could go either way, and your doctor may suggest trying to pass it with medical support before recommending a procedure. Above 6 millimeters, most stones will need some form of treatment to break them up or remove them.
Drink Enough to Produce 2.5 Liters of Urine Daily
Fluid intake is the foundation of passing a stone. The goal isn’t just “drink more water” but a specific target: enough fluid to produce at least 2.5 liters of urine per day. That typically means drinking around 3 liters of fluid daily, since you lose some to sweat and breathing. The American Urological Association uses this same threshold in its clinical guidelines for stone management.
Spread your intake throughout the day rather than drinking large amounts at once. Water is the best choice. The steady flow of urine helps push the stone through your urinary tract and prevents it from sitting in one place. If your urine is pale yellow to nearly clear, you’re likely hitting the target. Dark yellow urine means you need more fluid.
Medications That Help Stones Move
Your doctor may prescribe a type of medication called an alpha-blocker to help the stone pass. These drugs work by relaxing the smooth muscle in your urinary tract, reducing the squeezing contractions that can trap a stone in place. With the muscle relaxed, the tube widens slightly and allows fluid to flow more freely around the stone, pushing it along.
A large Cochrane review found that all types of alpha-blockers improved stone clearance rates compared to standard care alone. Patients taking these medications also had fewer hospitalizations. Calcium channel blockers, which relax smooth muscle through a different mechanism, have shown similar benefits for stones in the lower urinary tract.
This approach is called “medical expulsive therapy,” and it’s most effective for stones in the 4 to 6 millimeter range, where the stone has a reasonable chance of passing but could use some help. For very small stones, the medication may not add much benefit since they’ll likely pass anyway. For very large stones, medication alone won’t be enough.
Managing Pain While You Wait
Passing a stone can range from mildly uncomfortable to intensely painful, depending on its size and where it is. Anti-inflammatory pain relievers are the standard first-line option because they reduce both pain and the swelling in your urinary tract that makes passage harder. Your doctor can recommend appropriate pain relief based on your stone size and symptoms.
Pain tends to come in waves rather than staying constant. You may feel sharp cramping in your lower abdomen or pelvis as the stone moves, followed by periods of relief. A warm bath or heating pad on your lower abdomen can help during painful episodes. If pain becomes unmanageable with the medications you’ve been given, that’s a sign to contact your doctor, as it may indicate the stone is too large to pass or is causing a blockage.
Stay Active, but Keep It Light
Gentle movement helps. Walking, light stretching, yoga, and slow cycling can encourage a stone to shift through your urinary system faster than staying sedentary. The combination of gravity, core muscle engagement, and the jostling of movement all contribute. Avoid high-impact exercise like running or jumping, which can increase pain without speeding things up meaningfully.
How Long Passage Takes
The timeline varies significantly by stone size. In a study tracking 75 patients with observed stones, the average passage time was 8 days for stones 2 millimeters or smaller, 12 days for stones between 2 and 4 millimeters, and 22 days for stones 4 millimeters or larger. But averages can be misleading here. For 95% of stones in the 2 to 4 millimeter range to pass, it took up to 40 days.
That means passing a stone is rarely a quick process. You may have days with no symptoms at all, followed by a sudden episode of pain as the stone shifts. Many people pass their stone without even noticing the moment it comes out, especially with smaller stones. Your doctor may ask you to urinate through a strainer so you can catch the stone for analysis, which helps determine what type it is and how to prevent future ones.
Signs a Stone Won’t Pass on Its Own
Several warning signs suggest the stone needs medical intervention rather than more waiting. The most serious is a combination of obstruction and infection. If you develop a fever, chills, or cloudy and foul-smelling urine while trying to pass a stone, that’s an urgent situation. A blocked urinary tract plus an active infection can escalate to a dangerous bloodstream infection. The American Urological Association’s current guidelines call for urgent drainage of the kidney in this scenario before any attempt to remove the stone itself.
Other signs that watchful waiting isn’t working include complete inability to urinate, severe abdominal pain that doesn’t respond to pain medication, persistent nausea or vomiting, or no progress after several weeks of conservative management. Stones larger than 6 millimeters that haven’t budged after a reasonable trial period will almost certainly need a procedure.
What Happens If You Need a Procedure
For bladder stones that won’t pass, the most common approach is cystolitholapaxy, where a small scope is inserted through the urethra into the bladder. The stone is broken into smaller pieces using laser, ultrasound, or mechanical energy, and the fragments are flushed out. Recovery is typically quick, with most people returning to normal activities within a few days.
For very large bladder stones, open or minimally invasive surgery through a small abdominal incision may be necessary, though this is uncommon. Your doctor will also want to address whatever caused the stone to form in the first place, whether that’s an enlarged prostate, a neurological condition affecting bladder emptying, or a chronic infection. Without treating the underlying cause, bladder stones tend to come back.