Kidney stones leave your body through urine, traveling a specific path from the kidney through a narrow tube called the ureter, into the bladder, and finally out through the urethra. Most stones smaller than 4 mm pass on their own within about a month, though the process can range from painless to intensely painful depending on where the stone is and how big it is.
The Path a Stone Takes
A kidney stone starts as a tiny crystal formation inside the kidney, where concentrated urine allows minerals to clump together. The stone can sit in the kidney for weeks, months, or even years without causing any symptoms. Problems begin when it moves.
The first major hurdle is the ureter, a thin tube (only 3 to 4 mm wide in places) connecting each kidney to the bladder. When a stone drops into the ureter, the tube spasms and contracts to push it along, similar to how your digestive tract moves food. These spasms are what cause the intense, wave-like pain kidney stones are known for. The stone can get temporarily stuck at narrow points in the ureter, which blocks urine flow and causes the kidney to swell with backed-up fluid.
Once the stone reaches the bladder, the worst pain is usually over. The bladder is a much larger, flexible space, and the stone simply sits there until you urinate. You may feel a strong, frequent urge to go. When you do urinate, the stone passes out through the urethra. This final stage typically involves little to no pain, since the urethra is wider than the ureter.
What the Pain Feels Like at Each Stage
Stones sitting quietly in the kidney rarely hurt. The pain starts when a stone enters the ureter and blocks urine flow. You’ll feel a sharp, severe pain in your side and back, just below the ribs. As the stone moves lower in the ureter, that pain often shifts downward toward the lower abdomen and groin. It comes in waves rather than staying constant, because the ureter squeezes rhythmically around the stone.
You may also feel a burning sensation when you urinate, notice blood in your urine (which can look pink, red, or brown), or feel nauseous. The pain can change location or intensity as the stone moves, which is actually a good sign. It means the stone is progressing. The most painful stretch is generally while the stone is in the ureter. Once it drops into the bladder, many people feel dramatic relief within minutes.
How Size Affects Your Chances
Stone size is the single biggest factor in whether it will pass on its own. Research published in the American Journal of Roentgenology tracked spontaneous passage rates by size:
- 1 to 4 mm: About 72 to 87% pass naturally, averaging around 31 days.
- 5 to 6 mm: Around 60 to 72% pass naturally, but the timeline stretches to roughly 45 days.
- 7 mm and larger: Only about 47% pass on their own, and it can take up to 12 months. Most stones this size need medical intervention.
Location matters too. A stone already in the lower ureter, close to the bladder, is much more likely to pass than one stuck near the kidney.
What You Can Do to Help It Along
Drinking plenty of water is the most effective thing you can do at home. Higher fluid intake increases urine volume, which helps push the stone through the ureter. Aim for enough water that your urine stays pale yellow or clear throughout the day.
For stones in the 5 to 10 mm range, doctors sometimes prescribe a medication that relaxes the smooth muscle in the ureter walls, making it easier for the stone to slide through. Staying physically active (walking, for example) may also help, though the evidence is mixed. Over-the-counter anti-inflammatory pain relievers can manage the discomfort and also reduce swelling in the ureter, which gives the stone more room to pass.
Your doctor will likely ask you to strain your urine by urinating through a fine mesh strainer or into a glass jar. This lets you catch the stone when it comes out. Save it, because lab analysis can identify what the stone is made of. Knowing the composition (calcium, uric acid, or other types) helps your doctor recommend dietary or medication changes to prevent future stones.
When a Stone Won’t Pass on Its Own
If a stone is too large, won’t budge, or is causing complications like infection or a complete blockage, doctors have several ways to remove it. The approach depends on the stone’s size, location, and composition.
Shock wave lithotripsy is the least invasive option. A machine sends focused sound waves through your body to break the stone into smaller fragments that you can then pass naturally in your urine. It works best for smaller stones that show up clearly on X-rays. Stones made of certain materials, like cystine, don’t break up well with shock waves. It’s also not an option during pregnancy or for people with pacemakers.
For stones in the ureter or lower kidney, doctors can pass a thin, flexible scope up through the urethra and bladder to reach the stone directly. They either pull it out whole or break it apart with a laser first. You’re under anesthesia for this, and recovery typically takes a few days.
Very large stones (usually over 2 cm) may require a procedure done through a small incision in your back. A scope goes directly into the kidney to break up and remove the stone. This is more involved, with a longer recovery, but it’s the most effective option for big or complex stones.
Warning Signs That Need Urgent Attention
Most kidney stones, while painful, pass without serious complications. But certain symptoms signal that something more dangerous is happening. Fever or chills alongside kidney stone pain can indicate an infection trapped behind the blockage, which can become life-threatening quickly. Vomiting so severe that you can’t keep fluids down puts you at risk of dehydration. Complete inability to urinate means the stone may be fully blocking your urinary tract. Severe, unrelenting pain that doesn’t respond to pain medication also warrants emergency care, as it may mean the stone is firmly lodged and the kidney is swelling with backed-up urine.