Passing a kidney stone means a hard mineral deposit travels from your kidney, through the narrow tube connecting your kidney to your bladder (the ureter), into your bladder, and finally out of your body when you urinate. It’s a process that can take anywhere from a few days to several weeks, and it ranges from mildly uncomfortable to intensely painful depending on the stone’s size and where it gets stuck along the way.
How a Stone Moves Through Your Body
A kidney stone forms inside the kidney itself, where minerals in your urine crystallize and clump together. You won’t feel anything at this stage. The trouble starts when the stone drops out of the kidney and enters the ureter, a tube only about 3 to 4 millimeters wide. The ureter contracts in waves to push the stone downward, similar to how your digestive system moves food, and those contractions are what produce the signature pain.
The stone can get temporarily lodged at points where the ureter naturally narrows. When it does, urine backs up behind it, creating pressure in the kidney. This backup is what makes the pain so severe. Once the stone finally reaches the bladder, most of the pain stops. You may feel a frequent, urgent need to urinate, and you might notice some pressure or discomfort. From there, the stone exits through the urethra during urination. Most people describe the final exit as surprisingly painless compared to the journey through the ureter.
What the Pain Actually Feels Like
The pain of a passing kidney stone, called renal colic, is often described as one of the most intense pains a person can experience. It typically starts as a deep, intense ache in your flank, the area between your lower ribs and hip on the affected side. As the stone moves, the pain can shift and radiate to your back, groin, or lower abdomen.
Renal colic comes in waves. You might have a constant dull ache punctuated by sharp, stabbing surges that last 20 to 60 minutes at a time. The pain usually peaks about one to two hours after it begins. Between waves, you may feel relatively okay, which can be disorienting. Other symptoms that commonly appear alongside the pain include nausea, vomiting, blood in your urine (which may look pink, red, or brown), and a burning sensation when you urinate.
Where the pain settles gives clues about the stone’s location. Pain high in the flank usually means the stone is still in the upper ureter near the kidney. As it descends, the pain tends to move toward the groin and lower abdomen. Once you feel mostly bladder pressure and urinary urgency without the intense flank pain, the stone has likely reached the bladder.
How Long It Takes
The timeline depends heavily on the stone’s size. Small stones under 4 millimeters pass on their own in about 31 days on average. Stones between 4 and 6 millimeters take an average of 45 days, and roughly 60 percent pass without intervention. Stones larger than 6 millimeters can take up to a year if they pass naturally, though only about 20 percent of stones this size manage to come out on their own.
Location matters too. A stone already sitting in the lower part of the ureter, closer to the bladder, passes on its own about 79 percent of the time. A stone stuck in the upper ureter near the kidney passes without treatment only about 48 percent of the time. This is why imaging can be helpful: knowing where the stone is tells your doctor how likely it is to pass and how long you might be waiting.
Your Chances of Passing It Naturally
Stone size is the single biggest predictor of whether you’ll pass it without a procedure. Stones 1 to 4 millimeters in diameter pass on their own roughly 72 to 87 percent of the time. At 5 millimeters, the rate drops to about 60 percent. At 7 millimeters, it’s closer to 47 percent, and at 8 millimeters, about 56 percent of stones still pass spontaneously. Beyond that size, medical intervention becomes increasingly likely.
For stones in the 4 to 6 millimeter range, your doctor may prescribe a medication that relaxes the smooth muscle in the ureter, making it easier for the stone to slide through. A large meta-analysis found this approach increased the passage rate from 66 percent to 85 percent for stones at least 4 millimeters in size. For smaller stones, the medication didn’t show a meaningful benefit over waiting alone.
What You Can Do While Waiting
Drinking plenty of fluid is the single most important thing you can do during active stone passage. The goal is to produce enough urine to keep pushing the stone along. Aim for about 3 liters of fluid throughout the day. Water is ideal. You’ll know you’re drinking enough if your urine stays pale yellow or nearly clear.
Over-the-counter pain relief can help manage the waves of discomfort. Anti-inflammatory medications tend to work well because they reduce the swelling in the ureter wall around the stone, which helps with both pain and passage. A heating pad on the affected side can also provide some relief between pain waves. Staying moderately active, like walking, may help the stone move, though there’s no need to push yourself through severe pain.
Your doctor will likely give you a mesh strainer to urinate through so you can catch the stone when it finally comes out. Saving the stone matters because lab analysis can identify its composition, which helps guide dietary changes to prevent the next one.
What the Stone Looks Like
When the stone finally comes out, it may be surprisingly small. Most passed stones range from the size of a grain of sand to a small pearl. They’re usually yellow or brown, and the surface can be smooth, rough, or jagged depending on the type. Calcium-based stones tend to be rougher with an irregular shape, while uric acid stones are often smoother and darker. You’re looking for a small, hard object in the strainer that doesn’t dissolve in water.
When a Stone Won’t Pass on Its Own
If a stone hasn’t moved after four to six weeks, or if it’s too large to pass, your doctor will discuss procedural options. The most common approach for smaller stones uses sound waves directed from outside the body to break the stone into fragments small enough to pass naturally. For larger or more stubborn stones, a thin scope can be threaded up through the urethra and bladder into the ureter, where the stone is either grabbed or broken apart with a laser. Both are typically outpatient procedures with recovery times of a few days to a week.
Signs That Need Urgent Attention
Most kidney stones pass safely at home with pain management and fluids. But certain symptoms signal complications that need emergency care. Fever or chills alongside stone pain can indicate an infection trapped behind the stone, which can become serious quickly. Completely unmanageable pain that doesn’t respond to medication, an inability to keep fluids down due to vomiting, or a complete stop in urination all warrant an emergency visit. These situations can mean the stone is fully blocking the ureter, which can damage the kidney if it persists.
Preventing the Next One
Once you’ve passed one kidney stone, the risk of forming another is real but not inevitable. About 10 percent of people who’ve had a stone will have a recurrence within five years, and about 22 percent within ten years. Staying well-hydrated is the most effective prevention strategy. Aiming for 3 liters of fluid daily, consistently, reduces the concentration of stone-forming minerals in your urine. Dietary adjustments depend on the stone type, which is why saving and analyzing your stone is so valuable. Common recommendations include reducing sodium intake, eating moderate amounts of animal protein, and getting enough dietary calcium (which, counterintuitively, helps prevent the most common type of stone by binding to a compound called oxalate in your digestive tract before it reaches the kidneys).