Size is a determining factor in whether a kidney stone can pass naturally and how long it takes. Small stones (less than 4 mm) usually pass on their own in about 31 days. Larger stones typically take longer and may require medical intervention.

Kidney stones are solid masses that form when chemicals and minerals in your urine harden into a crystal.

These chemicals and minerals, such as calcium and uric acid, are always present at low levels. Excess usually gets flushed out with your urine. In some cases, however, you can have too much of them, and kidney stones can form.

Some cases of kidney stones have no known cause, but certain lifestyle and health factors can increase your likelihood of developing them. For example:

Men and people who have a family history of kidney stones are also more likely to develop them.

Common symptoms of kidney stones are:

  • severe pain in your back and sides, especially pain that comes on suddenly
  • blood in your urine
  • constant need to urinate
  • pain while urinating
  • cloudy or foul-smelling urine
  • only urinating a small amount or not at all

Kidney stones form in the kidney and then move into the ureter. The ureter is the tube that connects the kidney to the bladder and allows urine to flow. Small stones can usually pass naturally, but bigger stones might get stuck in the ureter, causing the above symptoms.

Read on to learn the factors that determine how long it takes to pass a kidney stone.

A couple factors determine how long you’ll spend waiting for a kidney stone to pass.

Size

Size of the stone is a major factor in whether it can pass naturally. Stones smaller than 4 millimeters (mm) pass on their own 80 percent of the time. They take an average of 31 days to pass.

Stones that are 4–6 mm are more likely to require some sort of treatment, but around 60 percent pass naturally. This takes an average of 45 days.

Stones larger than 6 mm usually need medical treatment to be removed. Only around 20 percent pass naturally. For stones of this size that do pass naturally, they can take up to a year to pass.

Location

While size is the main factor in whether stones will pass on their own, stone location in the ureter also makes a difference.

Stones that are in the end of the ureter closer to where it attaches to the bladder — rather than the end that attaches to the kidney — are more likely to pass on their own. Research shows that 79 percent of these stones pass on their own.

For stones in the end of the ureter closer to the kidney, approximately 48 percent of these stones pass without any medical treatment.

The best home remedy to encourage the stone to pass is to drink lots of fluids, especially plain water and citrus juices such as orange or grapefruit. The extra fluid causes you to urinate more, which helps the stone move and keeps it from growing. You should aim for at least 2 to 3 quarts of water per day.

Smaller stones are more likely to pass on their own, so you should take steps to keep the stone from growing. This includes eating a diet that’s low in salt, calcium, and protein.

However, you need all of these for your body to function properly, so talk with your doctor about an appropriate diet to help you pass the stone.

Passing a kidney stone can be very painful. Taking pain medication such as ibuprofen won’t speed up the process, but it can make you a lot more comfortable while passing the stone. A heating pad can also help.

If you have a fever, significant nausea, or are unable to keep down liquids without vomiting, you should seek medical care.

Likewise, if you have only one kidney or known kidney problems or damage, see a doctor immediately.

An infected kidney stone is a surgical emergency. If you notice any signs of infection, go to the hospital.

In some cases, you might need medication or a nonsurgical procedure to help the stone pass. Common medications and treatments are:

  • Calcium channel blockers. Calcium channel blockers are usually used for high blood pressure but can be used to help kidney stones pass. They stop the ureter from spasming, which helps relieve pain. They also help widen the ureter so the stone can pass more easily.
  • Alpha blockers. Alpha blockers are medications that relax the muscles in the ureter. This can help the stone pass more easily. Relaxing the muscles can also help relieve pain caused by spasms in the ureter.
  • Lithotripsy. Lithotripsy is a nonsurgical procedure where high-energy sound waves (also known as shock waves) are used to break up the stone. The waves are aimed at the kidney’s location and pass through your body. Once the stone is broken up, the pieces can pass more easily. You might be hospitalized for a day or two after lithotripsy.

Dehydration is also common with kidney stones and can require intravenous fluids. You should see your doctor immediately if you start vomiting or have other signs of severe dehydration.

If you think you might have a kidney stone, you should see your doctor as soon as possible. If you’re found to have one, your doctor can help you determine whether to try to pass the stone naturally, take medication, or get the stone surgically removed.

In some circumstances, your doctor might recommend immediate surgical removal without a waiting period. This will usually be because the stone is too big to pass naturally (larger than 6 mm) or is blocking urine flow. If the stone is blocking the flow of urine, it can lead to an infection or renal damage.

In other circumstances, your doctor might recommend waiting to see if you can pass the stone on your own. You should check in with your doctor often during this time to see if anything is changing, especially if you have new symptoms.

During the waiting period, your doctor might recommend surgery if the stone continues to grow, you’re having unmanageable pain, or you develop signs of infection, such as a fever. Infection, fever, kidney damage, intractable (hard to control) pain, or intractable vomiting are all indications for immediate surgery.

Kidney stones can be very painful, but they often resolve without medical treatment. If you think you have a kidney stone, see your doctor as soon as possible to help you decide the best course of action.

Generally speaking, the larger the stone, the longer it will take to pass on its own. You may be able to wait it out, or your doctor may recommend medical intervention.

Having a kidney stone makes you more likely to have more kidney stones in the future. To reduce your risk of developing more stones, make sure you drink enough water to keep your urine light yellow or clear, and eat a diet high in fruits and vegetables and low in salt.

Your doctor can help you figure out what diet and lifestyle changes are best for you.