Most kidney stones pass on their own within one to three weeks, though the exact timeline depends heavily on the stone’s size. Stones 2mm or smaller take an average of 8 days. Stones between 2 and 4mm average about 12 days. Stones 4mm and larger can take around 22 days, and some take over a month.
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
These are averages, not guarantees. Some people pass a small stone in a day or two. Others wait weeks for the same size stone. The important takeaway: even small stones can take longer than you’d expect, so don’t panic if yours hasn’t passed after a week.
Where the Stone Is Matters Too
A stone closer to your bladder has a much better chance of passing than one still high up near the kidney. Research published in the American Journal of Roentgenology found clear differences based on location in the ureter, the tube connecting the kidney to the bladder:
- Upper ureter (near the kidney): 48% pass on their own
- Mid ureter: 60% pass on their own
- Lower ureter (near the bladder): 75% pass on their own
- Right at the bladder junction: 79% pass on their own
If your doctor tells you the stone is already in the lower ureter, the odds are strongly in your favor. If it’s still high up, the wait will likely be longer and the chance of needing intervention is higher.
What You Can Do to Speed Things Up
Drinking plenty of fluids is the most straightforward thing you can do. The NHS recommends aiming for up to 3 liters (about 12 cups) of fluid per day. Water is ideal. The extra volume increases urine output, which helps push the stone along. Staying active and moving around, rather than lying in bed all day, also helps.
For stones between 4 and 10mm, your doctor may prescribe a medication that relaxes the muscles in the ureter, making it easier for the stone to slide through. In clinical trials, 85% of patients taking this type of medication passed their stone without surgery, compared to 66% on placebo. That’s a meaningful difference. For stones smaller than 4mm, though, the medication showed no benefit over doing nothing, likely because those stones are small enough to pass easily on their own.
Managing the Pain While You Wait
Kidney stone pain can be excruciating, often described as one of the worst pains people experience. The pain typically comes in waves as the stone moves and the ureter spasms around it. Anti-inflammatory pain relievers like ibuprofen are recommended as first-line treatment over opioids. They reduce pain more effectively within the first 30 minutes, require less follow-up medication, and cause fewer side effects, particularly less vomiting.
The pain isn’t constant for most people. You’ll likely have periods of intense cramping followed by stretches of relative calm. Pain that suddenly stops can mean the stone has passed into the bladder, where it usually exits with little or no discomfort.
The Four-Week Safety Window
Doctors generally allow two to four weeks for a stone to pass before recommending intervention. This isn’t an arbitrary number. The complication rate for stones left untreated beyond four weeks nearly triples, jumping to about 20%. Complete obstruction of the ureter, even without symptoms, can start damaging kidney function in as little as six to eight weeks.
If your stone hasn’t budged after four to six weeks, your doctor will likely recommend a procedure to either break it up or remove it. This is especially true for stones larger than 6mm, which rarely pass on their own.
Uric Acid Stones Are an Exception
Most kidney stones are calcium-based and can only leave your body by physically passing through the urinary tract. Uric acid stones are different. They’re the only type that can be dissolved with medication. By making the urine less acidic, these stones can gradually shrink and disappear. Small uric acid stones (under 7mm) may pass within three weeks, and surgery is typically considered only if they haven’t resolved after four to six weeks.
Signs You Need Emergency Care
Most kidney stones are painful but not dangerous. However, certain symptoms signal a potential complication like infection or complete blockage that needs immediate attention:
- Fever above 101.5°F (a sign of infection, which can become life-threatening quickly)
- Persistent vomiting that prevents you from keeping fluids down
- Pain so severe that over-the-counter medications can’t touch it
- Cloudy or foul-smelling urine
People with only one kidney, diabetes, or already reduced kidney function face higher risks from a stuck stone and should have a lower threshold for seeking care.
After the Stone Passes
Once the stone is out, try to catch it. Your doctor will likely ask you to urinate through a small strainer so the stone can be sent to a lab for analysis. Knowing the stone’s chemical makeup, whether it’s calcium oxalate, uric acid, or another type, helps determine why it formed and how to prevent the next one. About half of people who get a kidney stone will get another one, so this step matters.
Your doctor may also request a 24-hour urine collection, where you save all your urine over a full day. This test reveals whether your body is producing too many stone-forming minerals or too few of the substances that normally keep stones from forming. The results guide specific dietary or medication changes tailored to your type of stone.