Most kidney stones pass on their own within one to four weeks, but the timeline depends almost entirely on the stone’s size. Stones smaller than 3 mm often pass within days, while stones closer to 5 or 6 mm can take several weeks or may not pass at all without medical help. Knowing where your stone falls on that spectrum helps you understand what to expect and when waiting stops being a reasonable plan.
Passage Time by Stone Size
Size is the single biggest factor in how long you’ll be dealing with a kidney stone. A large study tracking nearly 400 stones found these passage rates over two time periods: roughly one month and five months.
- Smaller than 2.5 mm: 98% pass within about a month. These are the easiest stones to deal with, and most people pass them in just a few days.
- 2.5 to 3.4 mm: 92% pass within a month, and 98% pass given enough time. Still very likely to resolve on their own.
- 3.5 to 4.4 mm: 71% pass within a month, 81% within five months. This is where the timeline starts to stretch noticeably.
- 4.5 to 5.4 mm: Only 47% pass within a month, and 65% within five months. At this size, there’s roughly a one-in-three chance the stone won’t pass naturally at all.
- 5.5 to 6.4 mm: Just 21% pass within a month, and only 33% within five months. Most stones this size require intervention.
- 6.5 mm or larger: These rarely pass on their own. Only about 9% make it out within five months.
The practical takeaway: if your stone is 4 mm or smaller, the odds are strongly in your favor and you’ll likely pass it within a few weeks. Once you get above 5 mm, the math shifts, and your doctor will probably start discussing procedures rather than continued waiting.
Where the Stone Is Matters Too
A kidney stone doesn’t just drop straight from your kidney to your bladder. It travels through the ureter, a narrow tube about 10 to 12 inches long, and there are three points where the tube narrows further: where it connects to the kidney, where it crosses over blood vessels near the pelvis, and where it enters the bladder. Stones frequently get stuck at these bottlenecks.
Stones that have already made it to the lower third of the ureter (closest to the bladder) pass at much higher rates. Research from one institution found that lower ureter stones had an 88% passage rate within four weeks. Upper and mid-ureter stones took longer, with passage rates continuing to climb up to about two months before plateauing. If your imaging shows a stone near the bladder, you’re in better shape than if it’s still up near the kidney. A stone that’s both large (6 mm or more) and located in the upper ureter has the lowest chance of passing spontaneously.
What Helps a Stone Pass Faster
Drinking plenty of fluids is the most straightforward thing you can do. The goal is to keep urine flowing steadily so the stone has something pushing it along. Aim for around 3 liters (about 100 ounces) of fluid per day. Water is ideal. You’ll know you’re drinking enough when your urine stays pale yellow or nearly clear.
Your doctor may also prescribe a medication that relaxes the smooth muscle in your ureter, making it easier for the stone to slide through. A large meta-analysis found that this type of medication raised the overall passage rate from about 70.5% to 80.5% and shortened passage time by roughly three and a half days on average. The benefit is modest for very small stones that would pass easily anyway, but it can make a meaningful difference for stones in the 4 to 6 mm range where the outcome is less certain.
Staying physically active, rather than lying in bed, also helps. Walking and normal movement encourage the stone to keep traveling downward.
Managing Pain While You Wait
Kidney stone pain comes in waves. You might feel fine for hours, then get hit with intense cramping in your back or side that radiates toward your groin. This happens when the stone shifts and temporarily blocks urine flow, causing pressure to build in the kidney.
Anti-inflammatory pain relievers like ibuprofen are the preferred first choice. They work well for kidney stone pain specifically because they reduce the swelling and inflammation in the ureter wall, not just the pain signal. Compared to opioid painkillers, anti-inflammatories provide longer-lasting relief, cause fewer side effects like nausea, and reduce the need for additional rescue medication. Heat applied to your back or flank can also help between doses.
When Waiting Is No Longer Safe
Most kidney stones are painful but not dangerous. There are specific situations, though, where you need urgent medical attention rather than continued patience:
- Fever or chills: These suggest an infection behind the blockage. An infected, obstructed kidney can become a serious emergency quickly. Infection with obstruction requires intervention regardless of stone size.
- Pain that won’t respond to medication: If you can’t get your pain under control at home, you need help.
- You stop producing urine: This could mean complete blockage, especially concerning if you only have one functioning kidney.
- Nausea and vomiting so severe you can’t stay hydrated: Dehydration slows stone passage and can spiral.
Even without these red flags, near-total blockage of the ureter can start damaging kidney function within about two weeks. This is one reason doctors schedule follow-up imaging rather than letting you wait indefinitely.
Catch the Stone When It Passes
Once your stone reaches the bladder, the hard part is over. Passing it from the bladder out of your body is usually painless and may happen without you noticing, which is exactly why you should strain your urine. Your doctor will likely give you a mesh strainer or you can use a fine coffee filter. Every time you urinate, pour through the strainer and check for a small, hard fragment.
Capturing the stone lets a lab analyze its composition, which tells your doctor why you formed it and what dietary or medical changes can prevent the next one. When you do catch a stone, keep it dry. Don’t store it in liquid or tape it to anything, as both interfere with the analysis.
How Long Is Too Long to Wait
There’s no single cutoff, but general timelines based on the research give useful guidance. For stones in the lower ureter, if nothing has happened after four weeks, intervention is worth discussing. For stones in the upper ureter, doctors may watch for up to two months before recommending a procedure. These aren’t hard deadlines, but beyond them, the odds of spontaneous passage drop significantly and the risk of kidney damage from prolonged obstruction rises.
If your stone is under 4 mm, you can feel reasonably confident it will pass, though the wait can be miserable. If it’s 5 to 6 mm, it’s a coin flip, and your doctor will weigh your symptoms, kidney function, and imaging results to decide whether to keep waiting or act. Anything over 6.5 mm almost certainly needs a procedure.