A normal fasting blood sugar is below 100 mg/dL (5.6 mmol/L). That’s the benchmark for healthy adults who don’t have diabetes. If your result lands between 100 and 125 mg/dL, it falls into the prediabetes range, and 126 mg/dL or above on two separate tests points toward type 2 diabetes.
The Three Fasting Blood Sugar Categories
Fasting blood sugar is measured after you haven’t eaten for at least 8 hours, which is why it’s typically drawn first thing in the morning. The result places you into one of three categories:
- Normal: 99 mg/dL or below
- Prediabetes: 100 to 125 mg/dL
- Type 2 diabetes: 126 mg/dL or above
A single reading of 126 or higher doesn’t automatically mean you have diabetes. Your doctor will typically repeat the test on a different day to confirm. Prediabetes, on the other hand, is a real metabolic shift, not just a “borderline” result. About 80% of people with prediabetes don’t know they have it, and without changes to diet or activity, many progress to type 2 diabetes within several years.
How Fasting Glucose Relates to A1c
Your fasting blood sugar captures a single moment in time. Your A1c (also called hemoglobin A1c) reflects your average blood sugar over the previous two to three months. The two tests measure different things, and they don’t always tell the same story. Someone can have a normal fasting reading but an elevated A1c if their blood sugar spikes after meals.
For reference, an A1c of 6% corresponds to an average blood sugar of about 126 mg/dL, while an A1c of 7% corresponds to roughly 154 mg/dL. The diagnostic threshold for diabetes is an A1c of 6.5% or higher. If your fasting glucose is in the prediabetes range, your doctor may order an A1c to get a fuller picture of what your blood sugar has been doing over time.
Targets During Pregnancy
Pregnancy changes the numbers. For women being monitored for gestational diabetes, both the American College of Obstetricians and Gynecologists and the American Diabetes Association recommend a fasting blood sugar below 95 mg/dL. That’s a tighter window than the standard adult cutoff of 100. Post-meal targets are also stricter: below 140 mg/dL one hour after eating, or below 120 mg/dL at two hours.
These lower thresholds exist because even mildly elevated blood sugar during pregnancy can affect fetal growth and delivery outcomes. If you’re tracking blood sugar during pregnancy, those are the numbers your care team is watching.
Targets for Children
Children with diabetes have different goals than adults. Starting blood sugar targets for kids are generally 71 to 180 mg/dL during the day and 101 to 200 mg/dL at bedtime, though these vary based on age, activity level, and how much the pancreas is still functioning. The A1c goal for children is typically below 7%, unless the child is too young to recognize or communicate symptoms of low blood sugar, in which case the target may be loosened.
Why Your Morning Reading Might Be High
If you’re already monitoring your blood sugar and notice it’s higher in the morning than you’d expect, two biological patterns could explain it.
The first is called the dawn phenomenon. In the early morning hours, your body naturally releases cortisol and growth hormone to prepare you for waking up. These hormones nudge your liver to release stored glucose, which raises blood sugar before you’ve eaten anything. This happens in everyone, but if you have diabetes or prediabetes, your body may not produce enough insulin to counteract it. The result is a fasting number that seems too high even though you haven’t eaten in hours.
The second pattern, called the Somogyi effect, applies mainly to people who take insulin. If your blood sugar drops too low during the night (sometimes without waking you), your body responds with a surge of adrenaline, cortisol, and growth hormone to bring it back up. That rescue response can overshoot, leaving you with elevated blood sugar by morning. If you suspect this is happening, overnight glucose monitoring can help identify the drop.
How to Prepare for the Test
For a valid fasting blood sugar result, you need to go without food or drink for 8 to 12 hours before the blood draw. Water is the one exception, and staying hydrated can actually make the draw easier. Coffee, tea, and juice all count as breaking the fast, even if they’re unsweetened. Most people schedule the test first thing in the morning and skip breakfast until after the draw.
If you ate late the night before or accidentally had something in the morning, mention it when you arrive. A broken fast won’t produce a dangerous result, but it can give you a falsely elevated number that leads to unnecessary follow-up testing. Getting the prep right the first time saves you a second trip.