A healthy fasting blood glucose level is below 100 mg/dL, measured after at least eight hours without food or drink other than water. Two hours after eating, a normal reading stays below 140 mg/dL. These two numbers are the most important benchmarks for understanding where you stand.
Fasting Blood Glucose
Fasting blood glucose is the most common measurement and the one your doctor will check at a routine physical. Below 100 mg/dL is considered normal. Once you reach the 100 to 125 mg/dL range, you’re in prediabetes territory, meaning your body is starting to have trouble processing sugar efficiently. A fasting result of 126 mg/dL or higher on two separate tests indicates diabetes.
For children under two, the expected range is slightly different: 60 to 100 mg/dL. Adults typically fall between 74 and 106 mg/dL when fasting, though any result below 100 is considered healthy by diagnostic standards.
Blood Sugar After Meals
Your blood sugar naturally rises after you eat. That’s expected. What matters is how high it climbs and how quickly it comes back down. In a healthy person, blood glucose measured two hours after a meal should be below 140 mg/dL. If it lands between 140 and 199 mg/dL at the two-hour mark on a glucose tolerance test, that falls into the prediabetes range. A reading of 200 mg/dL or higher points toward diabetes.
Most people never notice these fluctuations because the body handles them automatically. Symptoms of high blood sugar, things like increased thirst, frequent urination, and blurred vision, typically don’t appear until levels exceed 180 to 200 mg/dL.
How Your Body Keeps Glucose Stable
Two hormones do most of the work: insulin and glucagon, both produced by the pancreas. When you eat and blood sugar rises, the pancreas releases insulin, which drives glucose into your muscle, fat, and liver cells for storage. When blood sugar drops between meals or overnight, the pancreas releases glucagon instead, signaling the liver to convert its stored glycogen back into glucose and release it into the bloodstream.
Your liver acts as the central fuel reservoir. It stores glucose when there’s plenty available and manufactures new glucose from amino acids and other byproducts when reserves run low, a process that keeps your blood sugar from crashing during sleep or a long gap between meals. In a healthy body, this system keeps glucose within a remarkably narrow range around the clock. Problems begin when insulin can’t do its job effectively, either because the pancreas isn’t producing enough or because cells have become resistant to its signal.
The A1C Test: A Longer View
While fasting glucose and post-meal glucose are snapshots, the A1C test shows your average blood sugar over the past two to three months. It measures the percentage of hemoglobin (a protein in red blood cells) that has glucose attached to it. The higher your blood sugar has been running, the higher the percentage.
A normal A1C is below 5.7%. Between 5.7% and 6.4% indicates prediabetes. An A1C of 6.5% or higher meets the threshold for a diabetes diagnosis. This test is useful because it isn’t affected by what you ate yesterday or whether you remembered to fast. It reveals patterns rather than a single moment in time.
When Blood Sugar Drops Too Low
Healthy blood sugar isn’t just about avoiding high numbers. A reading below 70 mg/dL is considered low, a condition called hypoglycemia. Below 54 mg/dL is classified as severely low and can become a medical emergency. Symptoms of a low include shakiness, sweating, confusion, irritability, and a rapid heartbeat.
For people without diabetes, significant hypoglycemia is uncommon. It’s far more frequent in people taking insulin or certain diabetes medications, where the dose can overshoot the body’s actual need. Skipping meals, exercising intensely, or drinking alcohol on an empty stomach can also push glucose lower than usual.
Healthy Ranges During Pregnancy
Pregnancy changes the thresholds. The body naturally becomes more insulin-resistant during pregnancy to direct extra glucose to the growing baby, which means some women develop gestational diabetes even without prior blood sugar issues. Screening typically happens between 24 and 28 weeks.
The initial screening uses a one-hour glucose challenge: you drink a sugary solution, and your blood is drawn an hour later. A result below 140 mg/dL is generally considered normal. A result of 190 mg/dL or higher is diagnostic for gestational diabetes on its own.
If your one-hour result falls between 140 and 189 mg/dL, a follow-up three-hour test is used. The targets for that test are tighter than what applies outside of pregnancy: a fasting level of 95 mg/dL or lower, below 180 mg/dL at one hour, below 155 mg/dL at two hours, and below 140 mg/dL at three hours. Two or more results above those cutoffs lead to a gestational diabetes diagnosis. These stricter thresholds reflect the fact that even moderately elevated blood sugar can affect fetal development.
Prediabetes: The Window to Act
The prediabetes zone, a fasting glucose of 100 to 125 mg/dL, a two-hour post-meal reading of 140 to 199 mg/dL, or an A1C of 5.7% to 6.4%, is where most people have the greatest opportunity to change course. At this stage, blood sugar regulation is impaired but not yet broken. Losing 5% to 7% of body weight and getting roughly 150 minutes of moderate physical activity per week has been shown to cut the risk of progressing to type 2 diabetes significantly.
Prediabetes rarely causes noticeable symptoms, which is why routine screening matters, especially if you have risk factors like a family history of diabetes, a sedentary lifestyle, or a body mass index above 25. Many people live with prediabetes for years without knowing it.
Quick Reference: Key Numbers
- Fasting glucose (normal): below 100 mg/dL
- Fasting glucose (prediabetes): 100 to 125 mg/dL
- Fasting glucose (diabetes): 126 mg/dL or higher
- Two hours after eating (normal): below 140 mg/dL
- A1C (normal): below 5.7%
- A1C (prediabetes): 5.7% to 6.4%
- A1C (diabetes): 6.5% or higher
- Low blood sugar: below 70 mg/dL
- Severely low blood sugar: below 54 mg/dL