Kidney stones pass through your urinary tract in four stages, moving from the kidney into the ureter, down to the bladder, and finally out through the urethra during urination. The whole process can take anywhere from a few days to several weeks, and the pain is heavily concentrated in the middle stages, not at the end. Most stones under 5 mm pass on their own without surgical intervention.
The Four Stages of Passing a Stone
A kidney stone forms when your urine becomes too concentrated, allowing mineral crystals to clump together. This part is painless. You can carry a stone in your kidney for months or even years without knowing it exists. The trouble starts when it moves.
In the second stage, the stone drops from the kidney into the ureter, a narrow tube about 25 to 30 centimeters long that connects each kidney to the bladder. This is where most of the pain happens. The ureter contracts in waves to push the stone along, producing sharp, cramping pain that typically hits your back, side, or lower abdomen on one side. The pain often comes in waves several times an hour, intensifying as the stone reaches points where the ureter naturally narrows.
Once the stone reaches the bladder, the severe pain usually subsides. What replaces it is pressure: a frequent, urgent need to urinate, sometimes with discomfort. The bladder is much wider than the ureter, so the stone is no longer wedged in a tight space. In the final stage, the stone exits through the urethra during urination. For most people, this last step involves little to no pain. If you’ve been dreading the moment it comes out, that part is usually the easiest.
How Size Determines Whether a Stone Will Pass
The single biggest factor in whether a stone passes on its own is its size. A study published in the American Journal of Roentgenology tracked spontaneous passage rates by stone diameter and found a clear pattern:
- 1 to 4 mm: 72% to 87% pass without intervention
- 5 mm: about 60% pass on their own
- 6 mm: roughly 72% pass spontaneously
- 7 mm: drops to 47%
- 8 mm: about 56% pass, though these often take significantly longer and cause more complications
The location of the stone matters too. Stones closer to the bladder when first detected are more likely to pass than those still high in the ureter near the kidney. Your doctor can determine both size and location with a CT scan, which is the standard imaging test for kidney stones and detects them with about 97% accuracy.
What You Can Do to Help the Process
Staying well hydrated is the most important thing you can do while waiting for a stone to pass. The goal is to produce enough urine volume to keep flushing the stone downward. The NHS recommends drinking up to 3 liters (about 100 ounces) of fluid per day. Water is the best choice. Spreading your intake throughout the day works better than drinking large amounts at once, since steady urine flow creates consistent pressure behind the stone.
Pain management is the other priority. Over-the-counter anti-inflammatory medications help reduce both pain and the swelling in the ureter that can slow a stone’s progress. Your doctor may also prescribe a medication that relaxes the smooth muscle of the ureter, making it easier for the stone to move through. A large meta-analysis of randomized controlled trials found that this type of medication increased the stone expulsion rate by 44% overall. The benefit was strongest for stones larger than 5 mm and had less measurable impact on smaller stones that were already likely to pass. Patients taking the medication also experienced shorter passage times and fewer episodes of intense pain.
Physical activity, while uncomfortable, is generally encouraged. Walking and gentle movement may help the stone shift. Lying still for extended periods won’t speed anything up.
How Long It Takes
Small stones (under 4 mm) typically pass within one to two weeks. Stones between 4 and 6 mm may take two to three weeks or longer. Anything larger can take a month or more, if it passes at all. The timeline varies significantly from person to person based on stone shape, ureter anatomy, and hydration levels.
Your doctor will likely ask you to strain your urine using a fine mesh cup or filter so you can catch the stone when it comes out. Saving it allows lab analysis to determine its composition, which helps guide prevention strategies. Calcium oxalate stones, uric acid stones, and struvite stones each have different dietary and medical approaches to keep them from forming again.
Signs That Something Is Wrong
Most kidney stones, even painful ones, pass without serious complications. But a stone that completely blocks the ureter can trap urine behind it, creating conditions for a kidney infection. This is a medical emergency. Watch for a high temperature, chills or shivering, extreme fatigue, or urine that is cloudy and foul-smelling. These symptoms suggest bacteria are building up behind the blockage, and the situation requires prompt treatment to prevent kidney damage.
Pain that becomes constant rather than coming in waves, or that is so severe you cannot sit, stand, or find any comfortable position, also warrants urgent evaluation. Bloody urine is common with kidney stones and not necessarily alarming on its own, but combined with fever or worsening pain, it signals a problem that needs attention quickly.