Most kidney stones pass on their own within one to six weeks, but the timeline depends heavily on the stone’s size and location. Stones 2mm or smaller take an average of 8 days. Stones between 2 and 4mm average about 12 days. Stones 4mm or larger can take three weeks or more, and some won’t pass without medical help.
Passage Time by Stone Size
Size is the single biggest factor in how long you’ll be waiting. A study tracking 75 patients with ureteral stones found these averages:
- 2mm or smaller: 8.2 days on average, with 95% passing within 31 days
- 2 to 4mm: 12.2 days on average, with 95% passing within 40 days
- 4 to 6mm: 22.1 days on average, with 95% passing within 39 days
Those are averages, and your experience could be shorter or longer. A separate study found that the cumulative passage rate for stones under 10mm was about 15% at two weeks, 72% at four weeks, and 98% at six weeks. In other words, most stones that are going to pass will do so within a month, but some stragglers take up to six weeks.
Your odds of passing a stone without intervention also depend on size. Stones 5mm or smaller pass spontaneously about 89% of the time. Stones between 5 and 10mm drop to around 68%. Beyond 10mm, spontaneous passage is unlikely.
Where the Stone Is Matters Too
A stone near the top of the ureter (the tube connecting your kidney to your bladder) has a much harder journey than one near the bottom. Research published in the American Journal of Roentgenology found that stones in the upper ureter pass on their own less than half the time, even small ones. Stones in the lower ureter pass about 75 to 79% of the time, and their success rate doesn’t depend much on size.
This means two people with identically sized stones can have very different experiences depending on where the stone is sitting when it’s first diagnosed on a CT scan. If your doctor tells you the stone is in the distal (lower) ureter, that’s a good sign for natural passage.
What the Four Stages Feel Like
A kidney stone doesn’t cause constant, identical pain from start to finish. It moves through distinct stages, each with its own sensation.
In the first stage, the stone is still inside the kidney. Formation itself is painless, but your kidney may spasm to push the stone out. This feels like a deep muscle strain in your back or side, coming in waves one to four times per hour.
The second stage is typically the worst. The stone enters the ureter and triggers intense, wave-like pain as the narrow tube contracts to push it along. This is the classic “renal colic” that sends people to the emergency room. The pain often radiates from the back down toward the groin.
In the third stage, the stone drops into the bladder. The sharp pain usually stops, which can feel like sudden relief. But the bladder now senses a foreign object, so you’ll feel strong, frequent urges to urinate even when your bladder isn’t full. Occasionally the stone can temporarily block the exit from the bladder, making it difficult to urinate.
The final stage is expulsion. Passing the stone through the urethra is typically painless or causes only mild discomfort. You may need to push slightly while urinating. Many doctors will ask you to strain your urine through a filter so the stone can be analyzed.
What Speeds Things Up (and What Doesn’t)
Staying well hydrated is the most straightforward thing you can do. The standard recommendation is to drink enough fluid to produce 2 to 2.5 liters of urine per day, which for most people means adding roughly 1.3 liters of water beyond their normal intake. More fluid means more urine flow, which helps push the stone along and prevents new crystals from forming.
Your doctor may prescribe an alpha-blocker, a type of medication that relaxes the smooth muscle in the ureter to give the stone more room to travel. A meta-analysis of 20 studies found this approach shortened passage time by about 3.6 days on average compared to no medication. The benefit is most pronounced for stones in the 5 to 10mm range.
Pain relievers like anti-inflammatory drugs are essential for comfort during passage, but they don’t actually speed the stone along. Clinical trials have consistently shown that while these medications reduce pain and ureteral inflammation, they have no measurable effect on passage time or success rates. They make the wait bearable, not shorter.
When a Stone Won’t Pass on Its Own
Doctors generally allow four to six weeks for a stone 4mm or smaller to pass before recommending a procedure. For stones between 4 and 7mm, the observation window is shorter, typically two to four weeks, because the odds of spontaneous passage are lower.
Certain symptoms signal that waiting is no longer safe. Fever or chills alongside stone pain can indicate a kidney infection, which is a medical emergency when the urinary tract is blocked. Complete inability to urinate means the stone is causing an obstruction. Persistent vomiting that prevents you from staying hydrated, or pain that doesn’t respond to medication, also warrants urgent evaluation. A prolonged blockage can cause the kidney to swell with backed-up urine, a condition called hydronephrosis that risks permanent kidney damage if left untreated.
If intervention is needed, the approach depends on the stone’s size and position. Options range from sound-wave therapy that breaks the stone into smaller fragments to a thin scope threaded up through the urinary tract to extract or laser the stone directly. Recovery from these procedures is usually quick, with most people returning to normal activities within a few days.
A Realistic Timeline to Expect
If you’ve just been diagnosed with a kidney stone, here’s a practical framework. The first few days are often the most painful, as the stone works its way through the ureter. By the end of the first week, about 1 in 6 stones has already passed. By two weeks, that number roughly doubles. By four weeks, nearly three out of four stones that are going to pass have done so.
The pain isn’t constant throughout this period. You’ll likely have episodes of intense discomfort lasting minutes to hours, separated by stretches of feeling mostly fine. Activity, hydration, and time of day can all influence when these waves hit. Keeping a log of your pain episodes and fluid intake can help both you and your doctor gauge whether the stone is making progress or has stalled.