Passing a kidney stone is the process of a small, hard mineral deposit traveling from your kidney through your urinary tract and out of your body. It can take anywhere from a few days to several weeks, and the pain ranges from barely noticeable to some of the most intense discomfort people experience. Stones smaller than 5 mm pass on their own about 78% of the time, while larger stones increasingly require medical help.
How a Stone Moves Through Your Body
A kidney stone forms inside the kidney when minerals in your urine crystallize and clump together. Many stones sit in the kidney for weeks or months without causing any symptoms at all. The trouble starts when a stone drops out of the kidney and enters the ureter, the narrow tube connecting your kidney to your bladder. The ureter is only about 3 to 4 mm wide, so even a small stone can get stuck or scrape along the walls as it moves.
Once the stone reaches your bladder, the worst pain is usually over. The bladder is a much larger space, and the urethra (the tube that carries urine out of your body) is wider than the ureter. At this stage, you may feel strong, frequent urges to urinate as your bladder works to push the stone out. The final step is urinating the stone out, which typically involves little or no pain, though you may need to push slightly harder than normal.
What the Pain Actually Feels Like
The signature pain of a kidney stone, called renal colic, happens when the stone gets stuck in the ureter and blocks urine flow. Your kidney swells with backed-up urine, and the ureter spasms as it tries to push the stone along. This creates a sharp, serious pain in your side and back, just below the ribs. As the stone moves lower in the ureter, the pain often shifts to your lower abdomen and groin.
The pain tends to come in waves rather than staying constant. You might have 20 to 60 minutes of intense cramping followed by a period of relief before the next wave hits. Many people also experience nausea, vomiting, and blood in their urine. The color of the urine can turn pink, red, or brown. Some people describe the pain as worse than childbirth or broken bones, though smaller stones can pass with only mild discomfort.
Size Determines Whether It Will Pass
The single biggest factor in whether a stone will pass on its own is its size. Research using CT imaging has mapped out the probabilities clearly:
- 1 to 4 mm: 78% pass spontaneously
- 5 mm: 60% pass spontaneously
- 5 to 7 mm: 60% overall passage rate
- 8 mm or larger: 39% pass spontaneously, with the rate dropping to 27% for stones 10 mm and above
Location matters too. A stone that has already traveled to the lower portion of the ureter, near the bladder, is much more likely to pass than one stuck near the kidney. Your doctor can determine both size and position with a CT scan or ultrasound.
How Long It Takes
Small stones (under 4 mm) often pass within one to two weeks. Stones in the 4 to 6 mm range can take two to three weeks or longer. For larger stones that do pass on their own, the process can stretch to four to six weeks. If a stone hasn’t passed after that window, or if it’s causing complications like infection or persistent blockage, your doctor will likely recommend a procedure to remove or break it up.
A medication that relaxes the smooth muscle in the ureter can sometimes speed things along. For stones larger than 5 mm, this type of medication shortened passage time by about two days on average in clinical trials. For stones between 6 and 10 mm, the benefit was even larger, cutting roughly six days off the timeline. The medication doesn’t dramatically change whether a stone passes, but it can make the process faster and less painful.
What You Can Do While Waiting
Drinking plenty of water is the most important thing you can do. Higher urine volume helps push the stone through and reduces the chance of it getting stuck. Aim for enough fluid to keep your urine pale yellow or clear. Over-the-counter pain relievers like ibuprofen help with both pain and the inflammation that swelling causes in the ureter. A heating pad on your back or side can ease muscle spasms between pain waves.
Your doctor will likely ask you to strain your urine through a fine mesh filter or cheesecloth every time you use the bathroom. Catching the stone matters more than people realize. Once you’ve had one kidney stone, you’re significantly more likely to develop another. A lab analysis of the stone reveals exactly what it’s made of, whether calcium oxalate, uric acid, or another mineral. That composition tells your doctor which specific dietary changes or medications will help prevent the next one. Without knowing what type of stone you produce, prevention advice stays generic and less effective.
Signs You Need Immediate Help
Most kidney stones pass at home with pain management and fluids, but certain situations call for an emergency room visit. If you develop a fever or chills along with stone symptoms, that suggests an infection behind the blockage, which can become dangerous quickly. If the pain becomes truly unbearable and isn’t responding to over-the-counter medication, the ER can provide stronger pain relief and anti-nausea treatment through an IV. Complete inability to urinate, persistent vomiting that prevents you from keeping fluids down, or blood in your urine that won’t stop are all reasons to seek immediate care rather than waiting it out.