Most kidney stones pass on their own without surgery. About 80% of stones in the upper urinary tract and 91% of stones in the lower urinary tract will eventually work their way out naturally, though the timeline ranges from a few weeks to a few months depending on size. When stones are too large to pass, doctors have several options: shock waves to break them apart from outside the body, a scope threaded up through the urinary tract to laser them into fragments, or a small incision in the back for the largest stones.
Which approach you end up with depends almost entirely on two things: how big the stone is and where it’s sitting.
When Stones Pass on Their Own
Stones 3 mm or smaller pass naturally about 98% of the time. At 4 mm, that drops to roughly 81%. At 5 mm, about 65% still make it out. Once a stone reaches 6 mm, only a third of upper urinary tract stones pass on their own, and at 6.5 mm or larger, the odds fall to just 9%. Location matters too: stones that have already traveled to the lower part of the ureter (closer to the bladder) have better odds at every size.
If your stone is small enough to pass, the process typically takes several weeks, though some stones can linger for a few months. During that time, the main priorities are pain control and staying hydrated to keep urine flowing.
Managing Pain While You Wait
Kidney stone pain, called renal colic, happens when a stone blocks urine flow and the ureter squeezes around it. Anti-inflammatory painkillers like ibuprofen and diclofenac are the first choice. Multiple large analyses covering thousands of patients have found that these work better than opioids, acetaminophen, or antispasmodic drugs for renal colic. In head-to-head comparisons, diclofenac provided more sustained relief at 60 minutes than morphine and led to less need for additional painkillers. Opioids are considered a second-line option if anti-inflammatories aren’t enough or can’t be used.
Medications That Help Stones Pass Faster
For stones between about 4 and 7 mm, your doctor may prescribe a medication that relaxes the smooth muscle in the ureter, the tube connecting your kidney to your bladder. This widens the passage and reduces spasms, giving the stone more room to move. The medication is typically taken once daily at bedtime for anywhere from one to six weeks, or until the stone comes out. It’s most effective for stones lodged in the lower portion of the ureter.
Shock Wave Lithotripsy
Shock wave lithotripsy (SWL) is the only fully noninvasive option for breaking up kidney stones. You lie on a table while a machine sends focused sound waves through your skin to shatter the stone into small fragments that you then pass in your urine over the following days and weeks. There are no incisions and no scopes entering your body.
SWL works best on stones smaller than 10 mm located in the kidney or upper ureter. Stones between 10 and 20 mm can sometimes be treated this way, but success depends on density, location, and body composition. Stones larger than 20 mm are generally not good candidates. The density of the stone on a CT scan is a useful predictor: stones measuring 900 Hounsfield units or less tend to break apart well, while those above 1,000 resist the shock waves. Body size also plays a role. When the distance from skin to stone exceeds 10 cm, failure rates climb regardless of other factors.
For lower pole kidney stones between 10 and 20 mm, SWL has a stone-free rate of about 73%, compared to roughly 90% for ureteroscopy. Once stones in the lower pole exceed 14 mm, SWL outcomes drop more sharply. Certain stone compositions, including calcium oxalate monohydrate and cystine stones, are harder to break with shock waves.
Ureteroscopy and Laser Lithotripsy
Ureteroscopy skips the skin entirely. Under general anesthesia, the surgeon passes a thin, flexible scope up through your urethra, into the bladder, and up the ureter to reach the stone. A laser fiber threaded through the scope breaks the stone into small pieces, which are then plucked out with a tiny basket. The whole procedure typically takes under an hour.
This approach handles a wider range of stone sizes and types than shock wave therapy. It’s particularly effective for stones in the mid and lower ureter and for harder stones that resist shock waves. For lower pole kidney stones between 10 and 20 mm, ureteroscopy achieves stone-free rates near 90%. Stones larger than about 16 mm in the lower pole start to challenge even this technique.
After ureteroscopy, a temporary tube called a ureteral stent is usually placed inside the ureter to keep it open while swelling goes down. The stent stays in for a median of about 8 days. While it’s in place, you may feel bladder pressure, urgency, or discomfort, which is normal. After removal, most people experience cramps or spasms for a few hours. About a quarter notice some blood in the urine or burning during the first few trips to the bathroom, but this typically clears within the first day. Some people have a dull ache in the flank or bladder area for one to five days that gradually fades.
Percutaneous Nephrolithotomy for Large Stones
When a stone is larger than 2 cm, or when shock waves and ureteroscopy have failed, doctors typically recommend percutaneous nephrolithotomy (PCNL). This involves making a small incision in your back, creating a channel directly into the kidney, and removing the stone through that opening. It’s the most invasive of the three surgical options, but it has the highest stone-free rate for large and complex stones.
The American Urological Association recommends PCNL as first-line treatment for kidney stones larger than 2 cm and for large branched stones that fill multiple parts of the kidney’s drainage system. For lower pole stones larger than 1 cm, PCNL consistently achieves higher clearance rates than either SWL or ureteroscopy. Recovery involves a hospital stay and takes longer than the other procedures, but for big stones it often gets the job done in a single session rather than requiring multiple rounds of less invasive treatment.
How Treatment Decisions Are Made
Your doctor will base the plan on a CT scan, which reveals the stone’s size, location, density, and your body composition. Here’s the general framework:
- Under 5 mm: Watchful waiting with pain management and possibly a muscle-relaxing medication. The vast majority pass naturally.
- 5 to 10 mm: Medication may help. If the stone doesn’t pass within a reasonable timeframe or pain becomes unmanageable, shock wave therapy or ureteroscopy is the next step.
- 10 to 20 mm: Ureteroscopy or shock wave therapy, depending on location and stone density. Ureteroscopy tends to have higher success rates, especially for lower pole and harder stones.
- Over 20 mm: PCNL is usually the best option, with the highest single-procedure clearance rate for stones this size.
If shock wave therapy fails to clear a stone completely, a second round can be attempted. If that also fails, ureteroscopy is the recommended next step.
Preventing New Stones
About half of people who form a kidney stone will form another one, so prevention matters. The single most effective measure is drinking enough fluid to produce at least 2.5 liters of urine per day. Both the European Association of Urology and the American Urological Association classify this as a strong recommendation. For people who form cystine stones, fluid requirements are even higher, with guidelines recommending 3.5 to 4 liters of fluid daily. Water is the best choice, and spreading intake evenly throughout the day, including before bed, helps keep urine dilute around the clock.