Passing a kidney stone means a hard mineral deposit travels out of your kidney, through the narrow tube connecting your kidney to your bladder (the ureter), into the bladder, and finally out of your body when you urinate. The whole process can take anywhere from one to three weeks depending on the stone’s size, and the pain it causes ranges from barely noticeable to among the most intense experiences people report.
How a Stone Forms and Starts Moving
Kidney stones develop when your urine becomes concentrated enough for minerals to crystallize and clump together. They can sit in the kidney for weeks, months, or even years without causing any symptoms at all. The trouble starts when a stone dislodges and begins moving into the ureter, a tube only about 3 to 4 millimeters wide. That’s when most people first realize something is wrong.
The Four Stages of Passage
The journey happens in a predictable sequence, though the timeline varies from person to person.
First, the stone drops from the kidney into the ureter. This is typically the most painful phase. The ureter’s walls stretch around the stone, and the smooth muscle lining the tube contracts forcefully to push it downward. If the stone gets stuck, those muscles can spasm. The sustained contraction produces lactic acid, which irritates surrounding nerve fibers and creates the intense, wave-like pain known as renal colic. You’ll usually feel this as a sharp pain in your side or lower back that can radiate to your abdomen or groin.
As the stone moves lower in the ureter, the pain often shifts. What started as flank pain may migrate toward the lower abdomen or groin as the stone gets closer to the bladder. The pain can change intensity, too, coming in waves rather than staying constant.
Once the stone reaches the bladder, there’s often a noticeable relief from the worst pain. But a new set of symptoms takes over: a persistent, urgent need to urinate, frequent trips to the bathroom, and sometimes only passing small amounts of urine each time.
Finally, the stone exits through the urethra during urination. The urethra is wider than the ureter, so this last stage is usually the least painful. Many people feel a brief sting or pressure, and then it’s over.
How Long It Takes
Stone size is the biggest factor in how long you’ll be dealing with symptoms. A stone smaller than 4 millimeters often passes within one to two weeks. Larger stones, around 5 to 7 millimeters, can take two to three weeks. Once a stone reaches the bladder, it typically exits within a few days. If a stone hasn’t passed within four to six weeks, that’s a signal to follow up with a healthcare provider about other options.
Size and Your Odds of Passing It Naturally
Not every stone will pass on its own. A study published in the American Journal of Roentgenology tracked spontaneous passage rates by stone size and found a clear pattern:
- 1 to 4 mm: about 78% pass without intervention
- 5 to 7 mm: about 60% pass on their own
- 8 mm or larger: only about 39% pass naturally
Stones under 5 millimeters have the best chance of working their way out. Once a stone reaches 9 or 10 millimeters, the odds drop sharply, and most people will need a procedure to break it up or remove it.
What You Can Do During the Process
Drinking plenty of water helps keep urine flowing and can nudge the stone along. Your doctor may prescribe a medication that relaxes the smooth muscle in the ureter walls, making it easier for the stone to slide through without as much spasm or pain. Over-the-counter pain relievers can help manage the discomfort, though severe episodes may need something stronger.
Your doctor will likely ask you to strain your urine so you can catch the stone when it comes out. A simple kitchen strainer or tea strainer works. Store the stone in a small plastic bag and bring it to your next appointment. Lab analysis of the stone’s composition helps determine why it formed, which guides prevention strategies so you’re less likely to go through this again.
How Doctors Confirm What’s Happening
If you go to the emergency room or urgent care with severe flank pain, the standard imaging test is a CT scan without contrast dye. It picks up kidney stones with 95 to 98% accuracy and shows both the stone’s size and exact location in the urinary tract. Those two details, size and position, are what determine whether you can wait for the stone to pass or need intervention.
Warning Signs of Complications
Most stones pass without lasting harm, but a stone that gets stuck in the ureter can block urine flow. That backup causes the kidney to swell, a condition called hydronephrosis, and creates an environment where bacteria can multiply. A kidney infection on top of a stone blockage is a medical emergency.
The symptoms overlap with ordinary stone pain but add a few distinct signals: a high fever, chills or shivering, extreme fatigue, and urine that looks cloudy or smells unusually foul. Blood in the urine is common with stones alone and isn’t necessarily cause for alarm, but any combination of fever and stone symptoms means you need immediate medical attention.