Most kidney stones pass on their own within one to six weeks, though small stones can sometimes clear in just a few days. The timeline depends primarily on the stone’s size and where it’s located in your urinary tract. Stones under 4mm have the best odds of passing without intervention, while anything over 6mm may need medical help.
How Size Affects Passage Time
Stone size is the single biggest factor in whether a stone will pass on its own and how long it takes. Stones are measured in millimeters, and even a difference of 2mm can dramatically change the outcome. Research published in the American Journal of Roentgenology found the following spontaneous passage rates based on stone size measured on CT scans:
- 2mm to 4mm: About 72% pass without intervention. These smaller stones typically clear within one to two weeks, though some pass in just days.
- 6mm: Still about 72% passage rate, but these stones take longer, often two to four weeks or more.
- 8mm and above: The passage rate drops to around 56%. Stones this size frequently require medical intervention and can take several weeks if they do pass on their own.
Location matters too. A stone that has already traveled from the kidney into the lower part of the ureter (the tube connecting your kidney to your bladder) is much closer to passing than one still sitting near the kidney. Stones in the lower ureter pass at higher rates and faster than those higher up.
What the Waiting Period Looks Like
When your doctor determines a stone is small enough to pass on its own, they’ll typically give it up to 30 days before reassessing. During this observation period, you may be prescribed medication to relax the ureter and help the stone move along. After 30 days, imaging is usually repeated to check whether the stone has moved, passed, or is stuck in place. If it hasn’t budged, your doctor will likely recommend a procedure to remove it.
The pain during this period is not constant. You’ll likely experience waves of intense cramping, called renal colic, as the stone moves through narrow sections of the ureter. These episodes can last anywhere from 20 minutes to over an hour, with pain-free stretches in between. Many people describe it as the worst pain they’ve experienced. Once the stone drops into the bladder, the sharp pain usually stops. Passing it from the bladder out through the urethra is typically much less painful, sometimes barely noticeable.
Managing Pain While You Wait
Anti-inflammatory painkillers like ibuprofen are the recommended first-line treatment for kidney stone pain. Clinical evidence shows they reduce pain more effectively than opioids within the first 30 minutes, cause less vomiting, and reduce the need for additional pain medication. Your doctor may suggest acetaminophen or stronger prescription painkillers as a backup if anti-inflammatories aren’t enough on their own.
Applying a heating pad to your lower back or side can also help with muscle spasms around the ureter. Hot baths or showers provide temporary relief for many people. The pain tends to be worst when the stone is actively moving, which is actually a good sign, since movement means progress.
How to Help a Stone Pass Faster
Staying well hydrated is the most important thing you can do. Drinking up to 3 liters of fluid per day helps flush the stone through your system by increasing urine flow. You can gauge whether you’re drinking enough by checking your urine color. It should be pale or nearly clear. Dark urine means you’re not drinking enough to keep things moving.
Light physical activity also helps. Walking, gentle stretching, and slow cycling can encourage a stone to move through the urinary tract faster. The combination of gravity and movement works in your favor. Avoid intense or high-impact exercise, though, as it can worsen pain without speeding things up.
Your doctor may also prescribe a type of medication that relaxes the smooth muscle in the ureter, making it easier for the stone to slip through. This is sometimes called medical expulsive therapy, and it’s most useful for stones in the 5mm to 10mm range that are borderline between passing on their own and needing a procedure.
Signs a Stone Won’t Pass on Its Own
Not every stone can be waited out. You should contact your doctor if you develop a fever or chills, which can signal an infection behind the blockage. Persistent nausea and vomiting that prevents you from keeping fluids down is another concern, since dehydration will only make things worse. Pain that doesn’t respond to medication, or blood in the urine that worsens rather than improves, also warrants a call.
Stones larger than 10mm almost never pass spontaneously and typically require a procedure. Even stones in the 6mm to 9mm range may need intervention if they haven’t moved after several weeks. The two most common procedures are shock wave therapy, which breaks the stone into smaller fragments from outside the body, and ureteroscopy, where a thin scope is passed through the urethra and bladder to reach and remove the stone directly. Both are outpatient procedures with recovery times of a few days to a week.
What Happens After the Stone Passes
Once the stone is out, pain resolves quickly. You may have some mild soreness or a burning sensation when urinating for a day or two, but the intense flank pain stops. Your doctor will likely ask you to strain your urine and catch the stone so it can be analyzed. Knowing the stone’s composition (calcium, uric acid, or another mineral) helps guide prevention strategies so you’re less likely to form another one.
About half of people who pass a kidney stone will develop another one within five to ten years. Keeping your daily fluid intake around 3 liters is the single most effective prevention measure, regardless of stone type. Depending on what your stone was made of, your doctor may also recommend dietary changes like reducing sodium intake or limiting certain high-oxalate foods.