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 pass without intervention roughly 76% of the time, while stones larger than 9 mm drop to about a 25% chance of passing naturally. Knowing where you fall on that spectrum shapes everything: how long to wait, how to manage the pain, and when a procedure becomes the better option.
Which Stones Pass on Their Own
Size is the single biggest factor in whether a kidney stone will pass without help. A study published in the American Journal of Roentgenology tracked spontaneous passage rates by millimeter and found a clear pattern: stones 1 to 4 mm in diameter pass on their own about 76% of the time. At 5 to 7 mm, the rate drops to around 60%. Once a stone reaches 8 mm or larger, the odds fall below 50%, and stones over 10 mm pass naturally only about 27% of the time.
Passing a stone typically takes anywhere from a few days to several weeks. Stones in the lower portion of the ureter, closer to the bladder, tend to pass faster than those still high up near the kidney. Your doctor may recommend a “watchful waiting” period of four to six weeks for smaller stones, as long as your pain is manageable and you aren’t showing signs of infection or complete blockage.
Managing the Pain While You Wait
Kidney stone pain, called renal colic, can be severe enough that people describe it as worse than childbirth. The pain comes in waves as your ureter squeezes to push the stone along, and it often radiates from your back and side down toward your groin.
Anti-inflammatory pain relievers like ibuprofen or naproxen are the preferred first-line treatment. They work by reducing the swelling and spasm in the ureter wall itself, not just masking the pain. A meta-analysis comparing pain relief options found that anti-inflammatories led to fewer side effects and less need for additional rescue medication compared to opioid painkillers. A heating pad on your back or side can also help between doses.
Medications That Help Stones Pass
For stones between 5 and 10 mm, your doctor may prescribe a medication that relaxes the smooth muscle in your ureter, making the tube wider and letting the stone move through more easily. The most commonly used drug in this category increased the stone expulsion rate by about 44% in a large meta-analysis of randomized controlled trials. The benefit was strongest for stones larger than 5 mm, while stones 5 mm or smaller didn’t see a meaningful improvement since most of those pass on their own anyway.
This approach, sometimes called medical expulsive therapy, is typically combined with a pain reliever and plenty of fluids. You may be asked to urinate through a strainer so the stone can be caught and analyzed. Knowing the stone’s composition helps guide prevention strategies later.
Drinking Enough Fluid
Hydration is the simplest and most effective thing you can do both during an active stone episode and for long-term prevention. The goal is to produce about 2.5 liters (roughly 80 ounces) of urine per day. For most people, that means drinking around 3 liters of fluid daily, since some water is lost through sweat and breathing.
Water is the best choice. Lemon water offers a small bonus because the citrate in lemons can help prevent certain types of stones from forming. Sugary drinks and sodas, on the other hand, have been linked to higher stone risk. During an active episode, staying well-hydrated helps keep urine flowing and gives the stone less opportunity to get stuck.
Dissolving Uric Acid Stones
One type of kidney stone can actually be dissolved without surgery. Uric acid stones, which make up about 5 to 10% of all kidney stones, form in acidic urine. By raising the urine’s pH to between 6.5 and 7.0, you create conditions where the stone gradually breaks down. This is typically done with a prescription alkalizing agent taken several times a day, with the dose adjusted based on regular urine pH testing.
Dissolution therapy requires patience. Depending on the stone’s size, it can take weeks to months. But it works well enough that many uric acid stones can be eliminated entirely without a procedure. This approach only works for uric acid stones, not for calcium-based stones, which are far more common.
Procedures for Larger Stones
When a stone is too large to pass, causing a complete blockage, or paired with signs of infection, a procedure becomes necessary. There are three main options, and the choice depends on the stone’s size and location.
Shock wave lithotripsy uses focused sound waves from outside the body to break a stone into smaller fragments that can then pass naturally. It works best for stones smaller than 2 cm located in the kidney or upper ureter. The procedure typically takes about an hour, and you go home the same day. You’ll pass stone fragments over the following days to weeks, which can still be uncomfortable.
Ureteroscopy involves passing a thin, flexible scope up through the bladder and into the ureter. The surgeon can either grab the stone with a small basket or use a laser to break it apart. There’s no incision, and it’s the go-to option for stones lodged in the ureter. Recovery usually takes a few days, though a temporary stent placed in the ureter can cause some discomfort until it’s removed.
Percutaneous nephrolithotomy is reserved for large stones, generally those bigger than 2 cm. The American Urological Association recommends it as first-line therapy for kidney stones over 2 cm. The surgeon makes a small incision in your back and uses a scope to remove the stone directly from the kidney. It requires general anesthesia and a hospital stay of one to two days, but it clears large stones more completely than the other options.
Dietary Changes That Prevent New Stones
About half of people who get a kidney stone will form another one within five to ten years, so prevention matters. The right dietary strategy depends on what kind of stone you had, which is why catching and analyzing the stone is so valuable.
For calcium oxalate stones, the most common type, the key foods to limit include spinach, rhubarb, nuts and nut products, peanuts, and wheat bran. These are all high in oxalate, a compound that binds with calcium in your urine to form crystals. Counterintuitively, you should not cut back on dietary calcium. Eating calcium-rich foods at meals actually helps, because calcium binds oxalate in the gut before it reaches your kidneys.
Reducing sodium intake also helps. High-sodium diets increase the amount of calcium your kidneys excrete, which raises stone risk. Limiting animal protein is another useful step, since protein from meat, poultry, and fish can make urine more acidic and increase both calcium and uric acid levels.
Signs That Need Immediate Attention
Most kidney stone episodes, while painful, resolve safely at home. But certain symptoms signal something more dangerous, like an infected, obstructed kidney, which can become life-threatening. Get medical help right away if you experience pain along with fever and chills, because this combination suggests infection behind a blockage. Other red flags include pain so severe you can’t sit still or find a comfortable position, nausea and vomiting that prevent you from keeping fluids down, visible blood in your urine, or difficulty passing urine at all. A complete blockage that stops urine flow can damage the kidney if it isn’t relieved promptly.