The hallmark sign of passing a kidney stone is sudden, intense pain in your side or back, just below your ribs, that shifts location over hours or days as the stone moves downward through your urinary tract. Most stones under 4 mm pass on their own within one to two weeks, though the process can take up to 40 days. Here’s how to recognize what’s happening in your body, what to expect at each stage, and when the situation needs medical attention.
Where the Pain Starts and How It Moves
A kidney stone only causes symptoms once it leaves the kidney and enters the ureter, the narrow tube connecting the kidney to the bladder. When the stone gets stuck or scrapes along this tube, it blocks urine flow, causes the kidney to swell, and triggers intense spasms. The pain is sharp, often described as worse than childbirth or a broken bone, and it typically hits in waves rather than staying constant.
The location of the pain tells you roughly where the stone is. It usually starts as a deep ache in the flank, the area of your back between the lower ribs and hip on one side. As the stone moves down the ureter toward the bladder, the pain migrates forward and downward, spreading into the lower abdomen and groin. Some people feel it radiate into the inner thigh or, in men, into the testicle on the affected side. Once the stone reaches the bladder, the worst pain often subsides. Passing it from the bladder out through the urethra is usually much less painful, sometimes barely noticeable.
Other Symptoms Beyond Pain
Pain gets most of the attention, but a passing stone causes several other noticeable changes:
- Blood in your urine. The stone irritates the lining of the ureter, so your urine may turn pink, red, or brown. Sometimes the blood is only visible under a microscope, but many people can see the color change clearly.
- Frequent, urgent urination. As the stone reaches the lower ureter near the bladder, it can mimic a urinary tract infection. You may feel like you constantly need to urinate but only pass small amounts.
- Burning during urination. This is most common in the final stage, when the stone is near or inside the bladder.
- Nausea and vomiting. The kidneys and gut share nerve pathways, so intense kidney pain frequently triggers nausea. This is a normal part of the process, not necessarily a sign of something more serious on its own.
- Cloudy or foul-smelling urine. This can indicate an accompanying infection, which changes the urgency of the situation.
Stones That Cause No Symptoms at All
Not every kidney stone announces itself with dramatic pain. Research published in The Journal of Urology found that a meaningful number of stones in the ureter are discovered incidentally, with no symptoms. In that study, about a third were found on imaging ordered for completely unrelated reasons. Another 20% were caught because routine lab work showed microscopic blood in the urine. Even among these “silent” stones, 65% of patients had some degree of kidney swelling from the blockage, meaning damage can occur without you feeling it. If you’ve had stones before, periodic imaging during follow-up visits can catch new ones early.
How Long the Process Takes
The timeline depends almost entirely on stone size. A study tracking 75 patients with ureteral stones found these averages:
- 2 mm or smaller: average of 8 days to pass
- 2 to 4 mm: average of 12 days to pass
- 4 mm or larger: average of 22 days to pass
Those are averages. For 95% of stones in the 2 to 4 mm range to clear, the window stretches to about 40 days. So if you’re at day 10 and still dealing with intermittent pain, that doesn’t mean something is wrong. The pain often comes in episodes rather than being continuous. You might have a terrible few hours, then feel mostly fine for a day or two before another wave hits as the stone shifts position.
Your Odds of Passing It Without a Procedure
Size is the single biggest factor in whether a stone will pass on its own. A study in European Radiology tracked spontaneous passage rates over 20 weeks and found a clear size threshold:
- 3 mm or smaller: 98% pass naturally
- 4 mm: 81% pass naturally
- 5 mm: 65% pass naturally
- 6 mm: 33% pass naturally
- 6.5 mm or larger: only 9% pass naturally
The practical cutoff most urologists use is around 5 to 6 mm. Below that, watchful waiting with pain management is the standard approach. Above that, you’re more likely to need a procedure. About half of all stones larger than 5 mm eventually require some form of intervention.
How Doctors Confirm It’s a Stone
If you go to the ER or your doctor’s office with symptoms, the gold-standard test is a CT scan of the abdomen and pelvis done without contrast dye. According to the American Urological Association, this type of scan detects ureteral stones with 98% sensitivity and 97% specificity, far better than ultrasound or X-ray alone. It also reveals the stone’s exact size and location, which determines whether you can wait it out or need treatment. An ultrasound is sometimes used first, especially in pregnant women or to avoid radiation exposure, but it misses smaller stones more often.
How to Catch the Stone When It Passes
Your doctor will likely ask you to strain every urination so the stone can be analyzed. The composition of the stone (calcium, uric acid, or other minerals) directly shapes the prevention plan to keep you from forming more. Mayo Clinic’s collection instructions are straightforward: urinate into a container or toilet insert, pour the urine through a fine mesh strainer or filter (your doctor’s office or pharmacy can provide one), and inspect what’s left behind.
Check carefully. The stone may be as small as a grain of sand or a tiny piece of gravel, tan or brown, and easy to miss. Filtering your first morning urine is especially important because stones often shift into the bladder or urethra overnight. Once you find something, place it in the specimen container your doctor provided, keep it dry, and bring it to your next appointment.
Signs That Need Immediate Attention
Most kidney stones, while painful, resolve without complications. But certain symptoms signal that the stone is causing a problem your body can’t handle alone. Fever or chills alongside stone symptoms suggest a urinary tract infection behind a blocked ureter. This combination can escalate into a serious bloodstream infection quickly. Vomiting so severe that you can’t keep down fluids leads to dehydration, which slows the stone’s passage and worsens your condition. Complete inability to urinate means the blockage may be severe. Pain so intense that over-the-counter medication can’t touch it is also worth an ER visit, both for relief and to rule out complications.
If you’ve had imaging that shows a stone larger than 6 mm and your symptoms aren’t improving after a few weeks, that’s a conversation to have with a urologist about whether it’s time for a procedure rather than continuing to wait.