Most people should schedule their first colonoscopy at age 45. That’s the current recommendation from the U.S. Preventive Services Task Force, the American Cancer Society, and the CDC. The starting age was lowered from 50 in 2018, and screening is recommended to continue through age 75.
Some people need to start much earlier. If you have a family history of colorectal cancer or certain genetic conditions, your first colonoscopy could be due in your 20s, 30s, or early 40s. And specific symptoms can warrant a colonoscopy at any age.
Why the Starting Age Dropped to 45
Colorectal cancer rates have been climbing steadily in younger adults. While rates in people over 50 have stabilized or even declined in many countries, incidence in the 25-to-49 age group keeps rising, and not just in Western nations. By 2030, an estimated 11% of colon cancers and 23% of rectal cancers will occur in people under 50.
Researchers point to a birth cohort effect: people born in 1960 or later face higher risk than previous generations, likely due to shifts in diet, obesity rates, and environmental exposures that aren’t yet fully understood. The U.S. was the first to lower its recommended screening age, and Australia followed in 2024 for its national program. The countries with the highest rates of early-onset colorectal cancer include Australia, Puerto Rico, New Zealand, the U.S., and South Korea.
When to Start Earlier Than 45
Family history is the most common reason to begin screening before 45. Having a first-degree relative (parent, sibling, or child) with colorectal cancer roughly doubles your risk. The specific timeline depends on when your relative was diagnosed:
- Relative diagnosed before age 60, or two or more relatives at any age: Start screening at 40, or 10 years before the age your youngest relative was diagnosed, whichever comes first. Repeat every 5 years with colonoscopy.
- One relative diagnosed at 60 or older: Start at 40, then follow the same schedule as average-risk individuals.
Inherited genetic conditions move the timeline even earlier. People with Lynch syndrome, which runs in families and significantly increases colorectal cancer risk, should begin colonoscopy between ages 20 and 25, or 2 to 5 years before the earliest cancer diagnosis in their family. Screening repeats every 1 to 2 years.
Symptoms That Call for Immediate Screening
Age guidelines apply to people with no symptoms. If you’re experiencing certain warning signs, a colonoscopy is appropriate regardless of how old you are. Research on early-onset colorectal cancer has identified four red-flag symptoms most strongly linked to a diagnosis: persistent abdominal pain, rectal bleeding, ongoing diarrhea, and iron deficiency anemia (which can show up as unusual fatigue, pale skin, or shortness of breath).
Less common but still notable signs include unexplained weight loss, changes in bowel habits that last more than a few weeks, bloating, and a feeling that your bowel doesn’t fully empty. These symptoms have many possible causes besides cancer, but they justify a conversation with your doctor about whether a colonoscopy makes sense.
Colonoscopy Isn’t the Only Option
A colonoscopy is the most thorough screening tool, but it’s not the only one. Stool-based tests can be done at home and are a reasonable alternative for people at average risk who prefer to avoid the procedure. The two main options are a fecal immunochemical test (FIT), done yearly, and a multitarget stool DNA test (often sold as Cologuard), done every three years.
The tradeoff is sensitivity. A large trial published in the New England Journal of Medicine found that the latest stool DNA test detected 93.9% of colorectal cancers and 43.4% of advanced precancerous lesions. FIT detected 67.3% of cancers and just 23.3% of advanced precancerous lesions. Colonoscopy remains the gold standard because it can both find and remove polyps in the same session. If a stool test comes back positive, you’ll need a follow-up colonoscopy anyway.
For people with a family history or genetic conditions, colonoscopy is the preferred method. Stool tests are generally recommended only for average-risk screening.
What to Expect From the Prep
The preparation is universally considered the worst part. You’ll follow a clear liquid diet the day before and drink a bowel-cleansing solution to empty your colon completely. The type of prep your doctor prescribes matters more than most people realize.
Traditional high-volume preps require drinking about 4 liters of solution and achieve adequate cleansing roughly 84% of the time. Newer low-volume options perform better. In a prospective comparison study, low-volume sodium sulfate preps reached adequate cleansing in about 91% of patients, and a combination of an over-the-counter laxative with a sports drink hit 92.5%. These smaller-volume preps were also rated significantly more tolerable. If your doctor defaults to an older prep, it’s worth asking about alternatives.
Most preps are now split-dose, meaning you drink half the evening before and the other half early the morning of the procedure. This approach improves both cleansing quality and the experience.
What Happens During the Procedure
The colonoscopy itself typically takes 20 to 40 minutes. You’ll receive sedation, and the level depends on your preference and what your facility offers. Conscious sedation keeps you drowsy but responsive. Deep sedation puts you to sleep entirely and requires an anesthesiologist or nurse anesthetist. Most people remember little to nothing either way.
During the procedure, a flexible camera is guided through the colon to look for polyps, which are small growths on the lining. If any are found, they’re usually removed on the spot. This is what makes colonoscopy uniquely effective: it’s both a diagnostic and preventive procedure, since removing precancerous polyps stops them from ever becoming cancer.
Plan for the rest of the day off. You’ll need someone to drive you home, and mild bloating or cramping afterward is normal. Most people eat a regular meal that evening and return to their usual routine the next day.
How Often You’ll Need to Repeat It
Your results determine when your next colonoscopy is due. If nothing is found, you won’t need another one for 10 years. If small polyps are removed, the interval shortens based on how many there were and what they looked like under a microscope:
- 1 to 2 small polyps (under 10 mm): Repeat in 7 to 10 years.
- 3 to 4 small polyps: Repeat in 3 to 5 years.
- 5 to 10 small polyps: Repeat in 3 years.
- Any polyp 10 mm or larger, or with concerning features: Repeat in 3 years.
- Large polyp removed in pieces: Repeat in 6 months to confirm complete removal.
These intervals assume a high-quality exam where the doctor had a clear view of the entire colon. If the prep was inadequate and parts of the colon couldn’t be seen well, your doctor will likely recommend repeating the procedure sooner. This is another reason good preparation matters: a poor prep can mean doing the whole thing over again within a year.
Screening Between Ages 76 and 85
After 75, routine screening is no longer a blanket recommendation. Whether to continue depends on your overall health, life expectancy, and screening history. Someone who has been screened regularly with consistently normal results faces less risk than someone who has never been screened. The decision becomes individual at this point, weighed against the small but real risks that any procedure carries as you age.