A normal fasting blood glucose level is 99 mg/dL (5.5 mmol/L) or below. That’s the number most people encounter first, since fasting glucose is the most common screening test. But “normal” shifts throughout the day depending on when and what you’ve eaten, and several different tests measure glucose in different ways.
Normal Fasting Glucose
Fasting blood glucose is measured after you haven’t eaten for at least eight hours, typically first thing in the morning. The CDC defines a normal result as 99 mg/dL or below. The Mayo Clinic uses a slightly tighter cutoff of less than 100 mg/dL (5.6 mmol/L), which is functionally the same threshold.
A fasting result between 100 and 125 mg/dL falls into the prediabetes range. At 126 mg/dL or higher on two separate tests, diabetes is diagnosed. These cutoffs exist because the risk of complications rises meaningfully once fasting glucose climbs above 100.
Normal Glucose After Eating
Blood sugar naturally rises after a meal, peaks around one to two hours later, then gradually returns to baseline. In a healthy person, glucose stays below 140 mg/dL (7.8 mmol/L) at the two-hour mark. This is the threshold used in the oral glucose tolerance test, where you drink a standardized sugar solution and have your blood drawn two hours later.
A two-hour reading between 140 and 199 mg/dL indicates prediabetes (sometimes called impaired glucose tolerance). A result of 200 mg/dL or higher points to diabetes. In real-world eating, your post-meal numbers will vary depending on the size, composition, and carbohydrate content of the meal, but the 140 mg/dL benchmark gives you a reference point.
A1C: Your Three-Month Average
The A1C test measures the percentage of hemoglobin in your red blood cells that has glucose attached to it, reflecting your average blood sugar over roughly two to three months. It captures the bigger picture rather than a single moment in time.
- Normal: below 5.7%
- Prediabetes: 5.7% to 6.4%
- Diabetes: 6.5% or above
An A1C of 5.7% corresponds roughly to an average glucose of about 117 mg/dL. Because it doesn’t require fasting, it’s a convenient screening option, though certain conditions like anemia or hemoglobin variants can affect accuracy.
What Continuous Glucose Monitors Show
Continuous glucose monitors (CGMs) have given researchers a detailed look at what happens in healthy, non-diabetic people throughout the day. In a multicenter study of healthy adults wearing CGMs, participants spent a median of 96% of their time with glucose between 70 and 140 mg/dL. That means even in people with perfectly normal metabolism, glucose occasionally dips below 70 or briefly rises above 140 after meals.
For people with diabetes using CGMs, the American Diabetes Association recommends spending more than 70% of the day in a wider range of 70 to 180 mg/dL. That broader target reflects the practical challenges of managing blood sugar with insulin or medication. Less than 4% of the day should be spent below 70 mg/dL, and less than 1% below 54 mg/dL.
When Glucose Drops Too Low
The floor matters too. Hypoglycemia in someone without diabetes is clinically defined as a blood glucose level below 55 mg/dL (3.0 mmol/L). Symptoms include shakiness, sweating, confusion, rapid heartbeat, and irritability. Most people start feeling “off” somewhere in the 60s, but the diagnostic threshold is set at 55 because that’s where the combination of symptoms, a confirmed low reading, and resolution after eating reliably come together.
Mild dips into the low 60s can happen in healthy people after prolonged fasting or intense exercise and aren’t necessarily a sign of a medical problem. Repeated episodes with symptoms below 55, however, warrant investigation.
How Your Body Maintains Normal Glucose
Your pancreas runs a tight feedback loop using two hormones. When you eat and blood sugar rises, beta cells release insulin, which signals your muscles and fat tissue to absorb glucose from the bloodstream. Insulin also tells the liver to store excess glucose as glycogen for later use.
Between meals or overnight, the process reverses. Alpha cells in the pancreas release glucagon, which tells the liver to break down stored glycogen and release glucose back into the blood. During longer fasts, glucagon also drives the liver (and to a lesser extent, the kidneys) to manufacture new glucose from non-carbohydrate sources like amino acids and lactate. This two-hormone system keeps blood sugar within a remarkably narrow window of roughly 70 to 100 mg/dL in the fasting state.
Tighter Ranges During Pregnancy
Normal glucose targets are lower during pregnancy. The American Diabetes Association and the American College of Obstetricians and Gynecologists recommend fasting glucose below 95 mg/dL, with post-meal readings under 140 mg/dL at one hour or under 120 mg/dL at two hours. These tighter targets exist because even moderately elevated glucose during pregnancy increases risks for both the mother and baby.
Gestational diabetes screening typically happens between 24 and 28 weeks of pregnancy using a glucose tolerance test. During the three-hour version, results are flagged as abnormal at 95 mg/dL fasting, 180 mg/dL at one hour, 155 mg/dL at two hours, and 140 mg/dL at three hours. Two or more abnormal values establish a diagnosis of gestational diabetes.
Quick Reference for Normal Ranges
- Fasting glucose: below 100 mg/dL (5.6 mmol/L)
- Two hours after eating: below 140 mg/dL (7.8 mmol/L)
- A1C: below 5.7%
- Hypoglycemia threshold: below 55 mg/dL (3.0 mmol/L)
- Pregnancy fasting target: below 95 mg/dL
These numbers apply to venous blood draws (standard lab tests). Home glucose meters and CGMs can vary by 10 to 15% from lab values, so small differences between your home reading and a lab result are expected.