Kidney stone pain typically starts in your flank, the area on either side of your lower back just below the rib cage. As the stone moves, the pain travels downward through your abdomen and into your groin. Where you feel it at any given moment depends on where the stone is sitting in your urinary tract.
How Pain Moves as the Stone Travels
A kidney stone that stays in the kidney itself often causes no pain at all. The trouble begins when it drops into the ureter, the narrow tube connecting your kidney to your bladder. From there, the location of your pain follows the stone like a tracking signal.
Flank and back: When a stone is still in the kidney or has just entered the upper ureter, you feel pain in your flank. This is higher than most people expect, sitting below the ribs and off to one side of your spine. It’s one key difference from ordinary back pain, which tends to center lower.
Lower abdomen: As the stone works its way down the middle portion of the ureter, pain shifts forward and downward into the lower abdomen on the affected side.
Groin and pelvis: When the stone reaches the lower ureter near the bladder, pain radiates into the groin or pelvic area. Men often feel it in the testicles. Women may feel it deep in the pelvis. This stage usually means the stone is close to passing, though the pain can still be severe.
Not everyone experiences this neat progression. Some people feel pain in multiple areas at once, and the intensity can spike suddenly at any point along the way.
Why It Hurts So Much
Kidney stone pain, clinically called renal colic, is notoriously intense. In a 2016 survey of 287 kidney stone patients, the average worst pain score was 7.9 out of 10, nearly identical to what first-time mothers report during labor (seven to eight out of 10). It’s not the stone scraping against tissue that causes most of the pain. The real culprit is a pressure buildup behind the stone.
When a stone blocks the ureter, urine backs up into the kidney. This causes the kidney’s outer covering to stretch, and the renal pelvis (the funnel-shaped collection area inside the kidney) to swell. That stretching activates pain receptors and triggers the release of inflammatory compounds called prostaglandins. Meanwhile, the muscles lining the ureter go into spasm, trying to push the stone along. Peak pressure from a complete blockage typically builds within two to five hours.
This combination of constant stretching and rhythmic muscle spasms creates two distinct layers of pain: a steady deep ache from the swelling, and sharp, wave-like surges from the ureter contracting. Those waves can last anywhere from 20 minutes to over an hour before easing, then return.
What the Pain Feels Like
Renal colic is different from most other kinds of pain. It comes in waves rather than holding steady, which is one of the clearest ways to tell it apart from a muscle strain or spinal problem. People describe it as stabbing, throbbing, or a deep pressure that makes it impossible to find a comfortable position. Sitting still, lying down, and standing all feel equally bad.
Typical low back pain from a muscle issue responds to position changes. You can usually find some posture that takes the edge off. Kidney stone pain does not work this way. The restlessness it causes is so characteristic that doctors consider it a hallmark sign.
Symptoms That Come With the Pain
Pain is rarely the only symptom. As the stone irritates the urinary tract, you may also notice:
- Pink, red, or brown urine (blood from irritation of the ureter lining)
- A constant, urgent need to urinate, especially as the stone nears the bladder
- Pain or burning during urination
- Being able to pass only small amounts of urine
- Cloudy or foul-smelling urine
- Nausea and vomiting, which often accompany the worst pain waves
The nausea isn’t coincidental. The kidneys and the digestive tract share nerve pathways, so intense kidney pain commonly triggers vomiting even though nothing is wrong with your stomach.
How Stone Size Affects What Happens Next
Most kidney stones pass on their own, but the odds depend heavily on size. A large European study tracking nearly 400 stones over 20 weeks found clear thresholds:
- 3 mm or smaller: 98% pass without intervention
- 4 mm: about 81% pass on their own
- 5 mm: about 65% pass
- 6 mm: only 33% pass
- 6.5 mm or larger: roughly 9% pass naturally
Stones under 4 mm are very likely to pass with time and pain management. Once a stone hits 5 to 6 mm, the probability drops sharply, and a procedure to break up or remove the stone becomes much more likely. About 1 in 5 patients in that study needed some form of intervention.
Signs That Need Immediate Attention
Most kidney stones are painful but manageable. A few situations signal something more dangerous, like an infection behind the blockage or a complete obstruction. These include pain paired with fever and chills, pain with persistent vomiting that prevents you from keeping fluids down, blood in your urine, or a complete inability to urinate. A kidney infection behind an obstructing stone can escalate quickly, so fever on top of flank pain is not something to wait out.