A kidney stone passes through your urinary tract in four stages, pushed along by rhythmic muscle contractions and the flow of urine. The entire process can take anywhere from one to three weeks for most stones, though smaller ones (under 4 mm) often pass within one to two weeks. The experience ranges from painless formation to intense flank pain to an urgent need to urinate, and understanding each stage helps you know what to expect and when something needs attention.
How the Stone Moves Through Your Body
Your ureters, the narrow tubes connecting each kidney to your bladder, move urine downward using wave-like muscle contractions called peristalsis. These contractions originate from natural pacemaker cells built into the smooth muscle of your kidney’s collecting system, meaning they happen automatically without signals from your brain or nervous system. When a stone dislodges from the kidney wall and enters the ureter, these same contractions work to push it toward the bladder, though the process is slower and more painful than normal urine flow because the stone creates a partial or full obstruction.
Urine building up behind the stone also creates pressure that helps force it downward. This combination of muscular squeezing and fluid pressure is what eventually moves the stone through each section of your urinary tract.
The Four Stages of Passage
Stage 1: Formation in the Kidney
Most kidney stones form silently. Minerals in your urine crystallize and gradually build into a solid mass attached to the inner wall of the kidney. You typically feel nothing during this phase and may not know a stone exists until it breaks free.
Stage 2: Into the Ureter
This is where the pain starts, and for most people, it’s the worst part. When the stone drops from the kidney into the ureter, you’ll likely feel a sharp, intense pain in your side or lower back. As the stone moves downward through the ureter, the pain tends to shift. It often starts as flank pain near your ribcage, then migrates toward your lower abdomen and groin as the stone descends. The pain comes in waves that match the ureter’s contractions squeezing around the stone. Nausea and vomiting are common during this stage.
Stage 3: Reaching the Bladder
Once the stone drops into your bladder, the sharp pain largely disappears. What replaces it is a feeling of intense pressure and a near-constant urge to urinate, sometimes as frequently as every five minutes. Your bladder is reacting to having a foreign object inside it, and the muscle spasms create that urgent sensation even when there’s little urine to pass.
Stage 4: Exiting Through the Urethra
The urethra is wider than the ureter, so this final stretch is usually the easiest physically. You may need to push harder than usual during urination to help the stone exit. The stone drops into the toilet, sometimes with a slight stinging sensation but rarely with the intense pain of the earlier stages. Once the stone reaches your bladder, it typically passes out within a few days.
How Long the Process Takes
Stones smaller than 4 mm generally pass within one to two weeks. Larger stones can take two to three weeks or more. If a stone hasn’t passed within four to six weeks, follow up with your provider, as it may need medical intervention to remove.
Where the stone sits in the ureter also matters. Stones closer to the bladder tend to pass faster than those lodged near the kidney, simply because there’s less distance to travel.
Size and Your Odds of Passing It Naturally
Stone size is the single biggest factor in whether you’ll pass it without a procedure. Research published in the American Journal of Roentgenology found the following spontaneous passage rates:
- 2 mm: 72%
- 4 mm: 72%
- 6 mm: 72%
- 8 mm: 56%
Stones under 6 mm have roughly the same likelihood of passing on their own. Once a stone reaches 8 mm or larger, the odds drop noticeably, and your doctor is more likely to recommend a procedure to break it up or remove it.
What Helps a Stone Pass Faster
Drinking plenty of fluid is the most straightforward thing you can do. More urine means more pressure behind the stone and more opportunities for those ureteral contractions to push it along. The NHS recommends drinking up to 3 liters (about 5 pints) of fluid per day to help move the stone and prevent new ones from forming. Water is the best choice, spread throughout the day rather than consumed all at once.
Your doctor may also prescribe a medication that relaxes the smooth muscle of the ureter, making it easier for the stone to slide through. A large systematic review in The BMJ found that patients taking these medications had a 76% stone passage rate compared to 48% in those who didn’t. The medication also shortened the time to passage by nearly four days on average. The benefit was especially pronounced for larger stones, where treated patients had a 57% higher likelihood of passing the stone compared to those without medication.
Staying physically active, rather than lying in bed, can also help. Movement encourages the stone to shift, and walking is often recommended between pain episodes.
Why You Should Catch the Stone
Your doctor will likely ask you to strain your urine through a fine mesh filter during the entire passage process. Pour each void through the filter and check carefully for particles. Kidney stones can be as small as a grain of sand, so look closely. Save anything solid in the container your provider gives you.
Analyzing the stone’s composition tells your doctor what type you’re dealing with, whether it’s calcium-based, uric acid, or something else. That information shapes the dietary and medical plan to prevent future stones, which matters because recurrence rates are high without targeted prevention.
Signs That Need Immediate Attention
Most kidney stones pass on their own with pain management and hydration, but certain symptoms signal a complication that can’t wait. Seek care right away if you experience pain so severe you can’t sit still or find a comfortable position, pain with fever and chills (which suggests infection), persistent vomiting that prevents you from keeping fluids down, blood in your urine, or difficulty passing urine at all. A stone that completely blocks urine flow or triggers an infection can damage the kidney quickly, and these situations sometimes require surgical intervention regardless of stone size.