Normal Blood Sugar Levels By Age (Chart) (2025)

A blood sugar test measures the amount of sugar circulating in the blood. Blood sugar, or glucose, is a vital health metric, as it’s the main source of energy for most cells in the body. When you eat food, that food is converted into glucose, which is then released into the bloodstream. Some foods affect blood sugar levels more than others. For example, carbohydrates raise your blood sugar levels more than proteins or fats.

Insulin is a hormone that regulates blood sugar levels within the body. When your blood sugar goes up, it signals your body to release insulin, which in turn helps glucose enter the cells to be used for energy.

Blood sugar levels are often discussed in the context of diabetes. Diabetes is a chronic condition in which the body either does not make enough insulin or does not use the insulin it produces properly, causing high blood sugar levels. Over time, this adverse effect can lead to an array of health issues.

“Consistently high blood sugar levels can signal metabolic conditions like diabetes, prediabetes or insulin resistance, which may increase the risk of complications such as heart disease, kidney disease, certain cancers and neuropathy,” explains Kara Burnstine, a registered dietitian nutritionist, certified diabetes educator and Forbes Health Advisory Board member. “Conversely, low blood sugar can cause symptoms like dizziness, confusion and even fainting.”

“Monitoring blood sugar helps maintain balance and reduces the risk of these health issues,” she adds. “Balanced blood sugars help maintain energy and focus throughout the day.”

For people with diabetes, monitoring blood sugar is an essential component of properly managing the disease. By tracking your levels, you not only keep tabs on whether your levels get too high or too low but can learn information about patterns that may impact your levels—such as the type of foods you eat and the timing of meals. This information helps your health care provider tailor a treatment plan that’s most effective for you.

Testing blood sugar levels can be done in a variety of ways. Below, Burnstine outlines the laboratory blood tests available, which she dubs as the “gold standard.” These tests, she explains, are highly accurate and are typically used for diagnosis and long-term monitoring by health care providers.

• Fasting blood glucose test: This test measures blood sugar after an eight-to-12-hour fast.
• Oral glucose tolerance test (OGTT): Measures how blood sugar responds to glucose intake over several hours.
• Hemoglobin A1C test: Reflects average blood sugar levels over the past two to three months.

For at-home monitoring of blood glucose levels, the following tests are available and widely used:

• Glucose meter (glucometer): This device takes a small sample of blood from your fingertip. These tests are “convenient for daily self-monitoring, but accuracy depends on proper technique, device quality and calibration,” says Burnstine.
• Continuous glucose monitor (CGM): A CGM is a device that measures your blood sugar levels every few minutes via a sensor placed under the skin, which Burnstine says is helpful for identifying long-term trends.

Keep in mind that fasting and non-fasting blood sugar tests have important differences, and each provide valuable information. Fasting blood sugar tests are taken after you have not eaten for at least eight hours, while non-fasting tests can be taken at any time.

“Fasting blood sugar is unaffected by recent food intake, providing a baseline to see if the levels are in normal range,” explains Burnstine. “Conversely, non-fasting levels reflect how well the body processes glucose from meals.”

It’s crucial to understand that normal blood sugar levels vary depending on age, lifestyle factors and health issues.

The chart below uses insight from studies including those conducted by the American Diabetes Association (ADA), the Centers for Disease Control and Prevention (CDC) and John Hopkins Medicine to illustrate the generally recommended blood sugar levels by age. It was reviewed by Jennifer Meller, M.D., chief medical officer at Sweetch—a digital health care innovation company based in Tel Aviv, Israel.

High Blood Sugar: Causes and Signs

High blood sugar, or hyperglycemia, can have a myriad of causes. According to the Centers for Disease Control and Prevention (CDC), these causes can include:

• Sickness
• Stress
• Eating more than usual
• Taking too much insulin

Signs of high blood sugar levels may include the following, according to the National Library of Medicine:

• Thirst
• Headaches
• Feeling tired or weak
• Frequent urination

If you’re feeling sick and your blood sugar is at or above 240 milligrams per decilitre (mg/dL), the CDC recommends testing at home for ketones with an over-the-counter kit. Ketones are a chemical byproduct of your body breaking down fat for energy, which can happen if there isn’t enough insulin. High ketones may be a sign of diabetic ketoacidosis, which is a medical emergency that warrants immediate attention.

Low Blood Sugar: Causes and Signs

The CDC defines low blood sugar levels as anything at or below 70 mg/dL. Low blood sugar levels, or hypoglycemia, come with a host of health issues. Hypoglecemia can be caused by the following factors, according to the CDC:

• Missing a meal
• Taking too much insulin or other diabetes medications
• Drinking alcohol
• Being more active than usual

The following signs may indicate a low blood sugar level, and they often occur quickly:

• Shaking
• Sweating
• Irritability/confusion
• Hunger
• Dizziness
• Nervousness/anxiety
• Fast or irregular heartbeat
• Inability to speak, see or hear properly

Populations more prone to developing hypoglycemia include those with type 1 diabetes, people who take insulin or other diabetes medications and people who are 65 or older, as well as those who have had previous bouts of low blood sugar and health issues such as heart or kidney disease.

If your blood sugar levels are too low, the CDC recommends following the 15:5 rule, which requires eating 15 grams of carbs, waiting 15 minutes, checking your blood sugar levels and then repeating the process if your levels are still under 70 mg/dL. Once your low blood sugar is addressed, the CDC recommends eating a balanced meal containing proteins and carbs.

The CDC considers a blood sugar level of under 55 mg/dL as severely low, warranting immediate medical attention and often an injectable glucagon. Contact a health care provider right away if your blood sugar is below the 55 mg/dL threshold.

The CDC notes that the optimal time for testing blood sugar levels depends on the type of diabetes you have (type 1 or type 2) as well as whether you take diabetes medication or insulin. Still, it notes the following intervals as common times to check your levels:

• Immediately upon waking up (before eating or drinking anything)
• Before a meal
• Two hours after a meal
• At bedtime

For those who don’t have diabetes, Burnstine recommends getting your blood sugar levels screened annually.