Most kidney stones pass on their own within one to six weeks, but the timeline depends almost entirely on the stone’s size. Stones smaller than 4 millimeters take an average of 31 days to pass, while stones between 4 and 6 millimeters average about 45 days. Stones larger than 6 millimeters rarely pass without medical help, and when they do, it can take up to a year.
Passage Time and Odds by Stone Size
Stone size is the single biggest factor in whether you’ll pass a stone naturally and how long it will take. Here’s what the numbers look like:
- Under 4 mm: About 80% pass on their own, averaging 31 days.
- 4 to 6 mm: Around 60% pass naturally, averaging 45 days.
- 7 to 9 mm: Only about 48% pass without intervention.
- Larger than 9 mm: Roughly 25% pass on their own, and those that do can take months.
If your doctor has told you a stone is 4 mm or smaller, the odds are strongly in your favor. But “passing on its own” doesn’t mean it happens quickly. Even small stones can take several weeks, and during that time you may experience waves of pain as the stone moves through the ureter, the narrow tube connecting your kidney to your bladder.
Where the Stone Is Matters Too
A stone’s location in the urinary tract changes the likelihood it will pass and roughly how long you’ll wait. Stones closer to the bladder have a much easier path. The spontaneous passage rate is 79% for stones right at the junction where the ureter meets the bladder, compared to just 48% for stones still sitting in the upper portion of the ureter near the kidney.
This is why imaging results often include the stone’s location. A 5 mm stone in the lower ureter is a very different situation from a 5 mm stone near the kidney. Your doctor uses both size and position to estimate whether watchful waiting makes sense or whether you’re likely to need a procedure.
What the Waiting Period Looks Like
If your stone is small enough to pass naturally, your doctor will typically recommend a 30-day observation period before reassessing with imaging. During this time, the goal is to manage pain, stay hydrated, and watch for signs the stone is moving.
Pain from kidney stones comes in episodes called renal colic. You might feel intense, cramping pain in your side or lower back that radiates toward your groin. These episodes can last anywhere from 20 minutes to several hours, then subside completely before returning. The pain corresponds to the stone shifting positions and temporarily blocking urine flow. Between episodes, you may feel completely fine, which can make the whole experience disorienting.
Anti-inflammatory pain relievers like ibuprofen are the recommended first-line treatment for stone pain and work better than stronger alternatives. Clinical evidence shows they reduce pain faster, cause fewer side effects like nausea and vomiting, and decrease the need for additional pain medication compared to opioid painkillers. If over-the-counter options aren’t controlling your pain, your doctor can prescribe stronger anti-inflammatory options.
How to Help a Stone Pass Faster
Drinking enough fluid is the most straightforward thing you can do. The goal is to produce 2.5 to 3 liters of urine per day, which generally requires drinking 3 to 4 liters of fluid daily. Water is ideal. This increased urine volume helps push the stone through the ureter. If you’re healthy and under 50, up to 5 or 6 liters a day is safe as long as it’s spread throughout the day, but most people don’t need to go that high. If you take any medications, especially diuretics for blood pressure, check with your doctor before dramatically increasing your water intake, since excess fluid can lower blood sodium levels.
Your doctor may also prescribe a medication that relaxes the smooth muscle in the ureter, making it easier for the stone to move through. These medications are used widely in practice, though the evidence on how much they actually speed things up is mixed. They tend to be most helpful for stones in the 5 to 10 mm range.
Staying physically active, rather than lying in bed, also seems to help. Movement encourages the stone to travel downward through the ureter.
Catching the Stone for Testing
Your doctor will likely ask you to strain your urine so the stone can be sent to a lab for analysis. The composition of the stone determines what dietary or medical changes can prevent future ones, which matters because about half of people who form a stone will form another within 10 years.
Use a fine-mesh strainer or a piece of fine gauze over a container every time you urinate. Straining your first morning urine is especially important since stones often pass into the bladder overnight while you’re lying down. A kidney stone can look like a tiny grain of sand or a small piece of gravel, so check carefully. When you find one, keep it dry in a small cup with a lid or a plastic bag. Don’t place it in liquid or stick tape to it, as both can interfere with lab analysis.
Signs You Need Immediate Help
Most kidney stones, even painful ones, are not emergencies. But a few specific situations require urgent medical attention. Fever is the most concerning symptom because it suggests an infection behind a blocked ureter, which is a potentially life-threatening combination that needs treatment right away.
You should also seek immediate care if you stop producing urine, develop severe nausea and vomiting that prevents you from keeping fluids down, experience confusion or extreme fatigue, or have only one functioning kidney. In any of these situations, waiting for the stone to pass on its own is no longer safe, and your doctor will likely recommend a procedure to remove or break up the stone.