A healthy fasting blood glucose level is below 100 mg/dL. That single number is the most widely used benchmark, but “healthy” depends on when you last ate, whether you’re pregnant, and what type of test you’re looking at. Here’s a breakdown of every number that matters.
Fasting Blood Glucose Ranges
Fasting blood glucose is measured after you haven’t eaten for at least 8 hours, typically first thing in the morning. The American Diabetes Association defines three categories:
- Normal: below 100 mg/dL
- Prediabetes: 100 to 125 mg/dL
- Diabetes: 126 mg/dL or higher
A single high reading doesn’t automatically mean diabetes. The test is usually repeated on a separate day to confirm the result. But if your fasting glucose consistently lands between 100 and 125 mg/dL, that’s prediabetes, a stage where your body is already struggling to manage blood sugar efficiently. At this point, changes to diet and physical activity can often bring numbers back into the normal range.
Blood Sugar After Eating
Your blood sugar naturally rises after a meal, peaking roughly one to two hours after you start eating. In a person without diabetes, that peak generally stays below 140 mg/dL. A reading between 140 and 199 mg/dL at the two-hour mark suggests impaired glucose tolerance, which is the post-meal equivalent of prediabetes. A reading of 200 mg/dL or higher points toward diabetes.
If you’re already managing diabetes, the targets are a bit more relaxed. The ADA’s 2025 guidelines recommend keeping post-meal glucose below 180 mg/dL and pre-meal glucose between 80 and 130 mg/dL. These targets apply to most nonpregnant adults, though your doctor may adjust them based on your age, how long you’ve had diabetes, and other health conditions.
The A1C Test: Your 3-Month Average
While a finger stick or blood draw captures a single moment, the A1C test reflects your average blood sugar over the previous 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 your A1C.
- Normal: below 5.7%
- Prediabetes: 5.7% to 6.4%
- Diabetes: 6.5% or above
A1C is particularly useful because it isn’t affected by what you ate that morning or whether you slept poorly the night before. It gives a broader picture of blood sugar control. For people already diagnosed with diabetes, the general goal is to keep A1C below 7%, though individualized targets vary.
What Continuous Glucose Monitors Show
Continuous glucose monitors (CGMs) measure blood sugar every few minutes through a small sensor worn on the skin. They’ve become popular not just for people with diabetes but for anyone curious about how their body responds to food and exercise. Instead of a single number, CGMs produce a concept called “time in range,” which tracks the percentage of the day your glucose stays within a target window.
A large community study of people without diabetes found that participants spent about 87% of their time in the 70 to 140 mg/dL range. Nearly 98% of their time fell within 70 to 180 mg/dL. If you’re using a CGM, those percentages give you a realistic sense of what healthy blood sugar patterns actually look like. Brief spikes above 140 mg/dL after meals are completely normal, as long as your glucose settles back down within a couple of hours.
When Blood Sugar Drops Too Low
Most conversations about blood sugar focus on numbers that are too high, but low blood sugar (hypoglycemia) is its own concern. Blood sugar below 70 mg/dL is considered low. Below 54 mg/dL is classified as severe and can cause confusion, seizures, or loss of consciousness.
Hypoglycemia is most common in people taking insulin or certain diabetes medications. It’s rare in people without diabetes. Symptoms include shakiness, sweating, a fast heartbeat, irritability, and sudden hunger. Eating or drinking something with fast-acting sugar, like juice or glucose tablets, typically brings levels back up within 15 minutes.
Healthy Ranges for Children
Children’s blood sugar targets differ from adults, partly because developing brains are especially vulnerable to both highs and lows. For children with diabetes, recommended ranges are:
- Ages 0 to 6: 100 to 200 mg/dL, with an A1C under 8.5%
- Ages 6 to 12: 90 to 180 mg/dL, with an A1C under 8%
- Ages 13 to 19: 90 to 150 mg/dL, with an A1C under 7.5%
These targets are wider for younger children because they’re less able to recognize or communicate symptoms of low blood sugar, so a slightly higher range reduces the risk of dangerous lows.
Blood Sugar During Pregnancy
Pregnant women are screened for gestational diabetes between 24 and 28 weeks. The screening involves drinking a sugary solution and having blood drawn one hour later. A result above 130 to 140 mg/dL (the exact cutoff varies by provider) triggers a longer, more detailed glucose tolerance test to confirm the diagnosis.
Gestational diabetes usually resolves after delivery, but it increases the risk of developing type 2 diabetes later in life. Women who are diagnosed typically monitor their blood sugar several times a day and manage it through diet, activity, and sometimes medication.
What Affects Your Numbers Day to Day
Blood sugar isn’t static. Even in perfectly healthy people, it fluctuates throughout the day based on dozens of factors. Food is the most obvious one, especially carbohydrates, which break down into glucose faster than protein or fat. But several other things move the needle:
- Sleep: A single night of poor sleep can temporarily increase insulin resistance, pushing fasting glucose higher the next morning.
- Stress: Physical or emotional stress triggers hormones that raise blood sugar, even if you haven’t eaten.
- Exercise: Physical activity pulls glucose into muscles for energy, which usually lowers blood sugar during and after a workout. Intense exercise can temporarily raise it.
- Illness: Infections and fevers commonly cause blood sugar to spike as part of the body’s stress response.
- Time of day: Many people have slightly higher fasting glucose in the early morning due to a natural surge of hormones that prepare the body to wake up.
A single reading outside the normal range isn’t necessarily a problem. Patterns matter more than any individual number. If your fasting glucose is creeping above 100 mg/dL on multiple occasions, or your A1C has crossed into the prediabetes range, that’s a signal your body’s ability to regulate blood sugar is changing and worth addressing early.