Most kidney stones pass on their own, but the timeline and strategy depend almost entirely on the stone’s size. Stones smaller than 5 mm have about a 90% chance of passing without any procedure. Stones between 5 mm and 10 mm drop to roughly 50-50 odds. Larger than that, you’re almost certainly looking at a medical procedure.
How Long It Takes to Pass a Stone
The wait is one of the hardest parts. For very small stones (2 mm or less), the average passage time is about 8 days. Stones between 2 and 4 mm take closer to 12 days. Once you hit 4 mm or larger, expect an average of around 22 days. These are averages, though, and the range is wide. For 95% of small stones to clear, it can take up to 31 days, and mid-sized stones can take 40 days.
Three factors predict how quickly a stone will pass: size, location, and which side it’s on. Stones that are already in the lower part of the ureter (closer to the bladder) pass faster. Stones on the right side also tend to move more quickly, though researchers aren’t entirely sure why. A stone still sitting high in the ureter near the kidney has a longer, more uncertain journey ahead.
What to Do While You’re Passing a Stone
Drink a lot of fluid. The goal is to produce enough urine to keep pushing the stone along. For prevention, the NHS recommends up to 3 liters (about 100 ounces) of fluid per day. During active passage, staying well above your normal intake helps maintain steady urine flow. Water is your best option. There’s no evidence that any particular beverage speeds things up. A study published in The Lancet’s eClinicalMedicine tested whether drinking fresh lemon juice twice daily (60 mL each time) could help prevent calcium oxalate stones, the most common type. The lemon juice group did no better than the group that simply followed a standard diet.
For pain, anti-inflammatory medications like ibuprofen or naproxen are the first-line choice. They work by reducing the swelling and spasm in the ureter wall, which is what actually causes the intense, wave-like pain (called renal colic). A large meta-analysis found that NSAIDs provide the most sustained pain relief with fewer side effects compared to opioids or acetaminophen. If over-the-counter doses aren’t cutting it, your doctor can prescribe stronger options.
Your doctor may also prescribe a medication that relaxes the smooth muscle of the ureter to help the stone pass. This class of drug was originally designed for prostate issues, but it works by widening the ureter slightly. A meta-analysis of randomized controlled trials found that this medication increases the overall stone expulsion rate by about 44%, and the benefit is strongest for stones larger than 5 mm. For stones 5 mm or smaller, the drug didn’t make a meaningful difference, likely because those stones are small enough to pass easily on their own. Patients who took it also experienced shorter passage times, less pain, and a lower chance of needing surgery.
When a Stone Won’t Pass on Its Own
If your stone is too large, hasn’t moved after several weeks, or is causing complications, there are three main procedures your doctor may recommend. The choice depends on the stone’s size and where it’s located.
Shock Wave Lithotripsy (SWL)
This is the least invasive option. You lie on a table while a machine sends focused sound waves through your body to break the stone into smaller fragments that you can then pass naturally. There’s no incision. It works best for stones that are smaller and located in the kidney or upper ureter. The stone-free rate is around 64%, meaning about a third of patients need retreatment. Recovery is relatively quick, though you’ll pass fragments over the following days or weeks, which can still be uncomfortable.
Ureteroscopy (URS)
A thin, flexible scope is passed through your urethra and bladder up into the ureter. The surgeon can either grab the stone with a small basket or use a laser to break it apart. No external incision is needed. This method has a significantly higher stone-free rate of about 82%, and only about 11% of patients need retreatment compared to 29% with shock wave therapy. It’s effective for stones throughout the ureter and for kidney stones up to about 2 cm. A temporary stent (a small tube) is often placed in the ureter afterward to keep it open while swelling goes down, which can cause some discomfort for a few days.
Percutaneous Nephrolithotomy (PCNL)
For large stones over 2 cm, this is the recommended first-line treatment. A surgeon makes a small incision in your back and passes a scope directly into the kidney to remove or break up the stone. It has the highest stone-free rate for large stones and the lowest retreatment rate, but it also carries more risk than the other two options, including a higher chance of bleeding. Hospital stays are typically one to two days. A newer version called mini-PCNL uses a smaller instrument, which results in fewer complications, less pain, and shorter hospital stays while achieving similar stone-free rates for stones up to 3 cm.
For stones in the lower pole of the kidney (the bottom section, where gravity works against you), both SWL and ureteroscopy have notably lower success rates. American Urological Association guidelines recommend that patients with lower pole stones larger than 1 cm be informed that PCNL offers the best chance of clearing the stone completely.
Signs You Need Immediate Help
Most kidney stone episodes, while painful, aren’t dangerous. But certain situations require urgent medical attention. Fever combined with a kidney stone suggests infection behind the blockage, which can escalate to sepsis quickly. This is a true emergency. Other red flags include having only one functioning kidney, blockage on both sides simultaneously, signs that your kidney function is declining (such as producing very little urine), or having a kidney transplant. Any of these situations typically requires hospital admission and an urgent procedure to relieve the blockage before treating the stone itself.
Preventing the Next One
About half of people who pass a kidney stone will get another one within five to ten years, so prevention matters. The single most effective thing you can do is drink enough fluid to produce at least 2.5 liters of urine per day, which generally means drinking close to 3 liters of fluid daily. Beyond hydration, prevention depends on what type of stone you had. If you can catch your stone (using a strainer when you urinate), your doctor can analyze its composition and tailor dietary recommendations. Calcium oxalate stones, the most common type, are influenced by sodium intake, animal protein consumption, and oxalate-rich foods like spinach, nuts, and chocolate. Reducing sodium is often more impactful than reducing calcium, since high sodium actually increases calcium levels in your urine.