Kidney stones move through your urinary tract because of a combination of muscle contractions in the ureter and the pressure of urine building up behind the stone. A stone sitting in the kidney can remain painless for months or even years, but once it drops into the ureter (the narrow tube connecting the kidney to the bladder), these forces work together to push it downward.
How Your Ureter Pushes Stones Along
The primary force that moves a kidney stone is peristalsis, the same type of wave-like muscle contraction that moves food through your digestive tract. Your ureter has its own muscular wall made of circular and longitudinal muscle bundles, and it contracts rhythmically to push urine from the kidney to the bladder. These contractions don’t require any signal from your brain or nervous system. They originate from built-in pacemaker cells located in the kidney’s collecting system and fire automatically. Even a segment of ureter removed from the body will continue contracting on its own.
When a stone enters the ureter, these contractions squeeze around and behind it, nudging it downward with each wave. The stone also irritates the ureteral lining, which can trigger stronger, more frequent contractions. This is a double-edged sword: those intensified contractions are what cause the severe, cramping pain of a kidney stone episode, but they’re also what drives the stone toward the bladder.
The Role of Urine Pressure
Fluid pressure matters just as much as muscle contractions. As your kidneys continuously produce urine, that fluid collects behind a stone that’s partially or fully blocking the ureter. The resulting hydrostatic pressure pushes against the stone from above, helping force it downward. This is why staying well hydrated is one of the most practical things you can do while passing a stone. More fluid means more urine production, which means more pressure behind the stone.
People who have had a kidney stone are generally advised to drink at least 2 liters (about 8 cups) of water per day, and ideally 3 liters (12 cups). During active passage, keeping your fluid intake high gives your body more force to work with.
Where Stones Get Stuck
The ureter is only about 3 to 4 millimeters wide at its narrowest points, and there are three spots where stones are most likely to stall. The first is at the ureteropelvic junction, where the kidney’s collecting area funnels into the ureter. The second is where the ureter crosses over the pelvic brim (the rim of the hip bone). The third, and often the tightest, is at the ureterovesical junction, where the ureter tunnels through the bladder wall. A stone can pause at any of these bottlenecks for days or weeks before the combination of peristalsis and urine pressure finally pushes it through.
Size Determines Whether a Stone Passes
The single biggest factor in whether a stone moves all the way through on its own is its diameter. Stones 1 millimeter across pass spontaneously about 87% of the time. For stones between 2 and 4 millimeters, that rate drops to 76%. Stones 5 to 7 millimeters still have a 60% chance of passing, while stones 7 to 9 millimeters pass about 48% of the time. Once a stone exceeds 9 millimeters, only about 25% pass without intervention.
Timeline follows a similar pattern. A stone smaller than 4 millimeters may pass within one to two weeks. Larger stones can take two to three weeks. Once any stone reaches the bladder, it typically passes within a few days, since the urethra is wider than the ureter. If a stone hasn’t passed within four to six weeks, that’s generally the point where your provider will discuss procedural options.
Medications That Relax the Ureter
Doctors sometimes prescribe a type of medication called an alpha blocker to help a stone pass. These drugs work by relaxing the smooth muscle in the ureter wall, widening the channel and reducing the spasms that cause pain. A large systematic review in The BMJ found that patients taking alpha blockers passed their stones about 3.8 days sooner on average compared to those who didn’t, and were 49% more likely to pass the stone overall.
Interestingly, the benefit was most pronounced for larger stones. Patients with bigger stones who took alpha blockers had a 57% higher likelihood of passing them compared to controls. For very small stones (which already pass easily on their own), the medication didn’t offer a meaningful advantage. So if your doctor prescribes one, it’s likely because your stone is in that middle range where a little extra help can make the difference between passing it naturally and needing a procedure.
How to Tell a Stone Is Moving
Pain location is the clearest indicator that a stone is on the move. When a stone first enters the ureter from the kidney, pain typically starts in the flank, at the side of your lower back. As the stone migrates downward, the pain often shifts toward the front of your body and into the lower abdomen or groin. This migration of pain from back to front over hours or days is a reliable sign that the stone is making progress.
When the stone reaches the lowest part of the ureter near the bladder, symptoms shift again. You may feel a strong, frequent urge to urinate, or a burning sensation that mimics a urinary tract infection. These bladder-like symptoms are actually a good sign: they mean the stone is close to exiting the ureter. Once it drops into the bladder, the intense flank pain usually resolves quickly, and you’ll pass the stone during urination, sometimes without even noticing it.
Physical Activity and Gravity
You may have heard that jumping, jogging, or walking can help a stone move, and there’s some practical logic behind this. Gravity and physical jostling can help a stone that’s loosely lodged shift position, especially if it’s sitting at one of the ureter’s narrow points. Walking is commonly recommended during stone episodes not just for comfort but because upright movement keeps gravity working in your favor. There’s no strong clinical evidence that any specific exercise dramatically speeds passage, but staying active (as much as pain allows) is generally preferable to lying still for days.
The bottom line: your stone moves because of rhythmic muscle contractions in the ureter, the pressure of urine accumulating behind it, and gravity. You can support all three of those forces by drinking plenty of water, staying physically active, and using prescribed medications if your stone is large enough to benefit from them.