A normal fasting blood sugar level is below 100 mg/dL, and a normal reading two hours after eating is below 140 mg/dL. These thresholds separate healthy glucose metabolism from prediabetes and diabetes, and understanding where your numbers fall can help you catch problems early or track an existing condition.
Normal Blood Sugar Levels
Blood sugar fluctuates throughout the day. It’s lowest after you haven’t eaten for several hours and rises after meals as your body breaks down carbohydrates into glucose. In a person without diabetes, the body keeps these swings within a relatively tight window.
A fasting blood sugar (taken after at least 8 hours without food) below 100 mg/dL (5.6 mmol/L) is considered normal. After eating, blood sugar rises but should stay below 140 mg/dL (7.8 mmol/L) within two hours. Between meals, most healthy adults hover somewhere in the 70 to 100 mg/dL range without thinking about it, because insulin is doing its job automatically.
Prediabetes and Diabetes Thresholds
Doctors use three main tests to evaluate blood sugar, each with its own cutoffs for prediabetes and diabetes.
Fasting Blood Sugar Test
- Normal: below 100 mg/dL
- Prediabetes: 100 to 125 mg/dL
- Diabetes: 126 mg/dL or higher on two separate tests
Oral Glucose Tolerance Test
This test measures your blood sugar two hours after drinking a sugary solution. It reveals how efficiently your body clears glucose from the bloodstream.
- Normal: below 140 mg/dL
- Prediabetes: 140 to 199 mg/dL
- Diabetes: 200 mg/dL or higher
A1C Test
Unlike the other two tests, A1C reflects your average blood sugar over the past two to three months rather than a single moment. It’s reported as a percentage.
- Normal: below 5.7%
- Prediabetes: 5.7% to 6.4%
- Diabetes: 6.5% or higher on two separate tests
A result in the prediabetes range doesn’t mean diabetes is inevitable. It means your body is starting to struggle with insulin, and lifestyle changes like improved diet and regular exercise can often reverse the trend.
When Blood Sugar Drops Too Low
Blood sugar below 70 mg/dL is considered low, a condition called hypoglycemia. This is most common in people taking insulin or certain diabetes medications, though it can occasionally happen in people without diabetes after prolonged fasting or intense exercise.
Symptoms of low blood sugar include shakiness, sweating, confusion, irritability, and a fast heartbeat. These are your body’s alarm signals that your brain isn’t getting enough fuel. A reading below 54 mg/dL is classified as severely low and can lead to seizures, loss of consciousness, or the inability to treat yourself. At that point, someone else may need to help you by providing glucose tablets, juice, or an emergency glucagon treatment.
When Blood Sugar Climbs Too High
On the other end of the spectrum, high blood sugar (hyperglycemia) often produces no symptoms at all until levels climb above 180 to 200 mg/dL. That’s one reason diabetes can go undiagnosed for years. When symptoms do appear, they typically include increased thirst, frequent urination, blurred vision, fatigue, and headaches.
If blood sugar stays above 240 mg/dL and ketones are present in the urine, the situation becomes more urgent. Ketones are acids your body produces when it starts burning fat instead of glucose for energy, and high levels can lead to a dangerous condition called diabetic ketoacidosis. Persistent readings at that level warrant immediate medical attention.
Targets for People Managing Diabetes
If you already have diabetes, your targets are different from the “normal” ranges used for diagnosis. The goal isn’t to perfectly mimic a non-diabetic body at every moment. It’s to keep blood sugar in a safe window as much as possible while avoiding dangerous lows.
For most adults with Type 1 or Type 2 diabetes, the standard target range is 70 to 180 mg/dL. If you use a continuous glucose monitor (CGM), the goal is to spend at least 70% of the day within that 70 to 180 mg/dL window, with less than 4% of the day below 70 mg/dL and less than 5% of the day above 250 mg/dL. These “time in range” goals give a more complete picture than any single fingerstick reading, because they capture how stable your blood sugar is across the whole day and night.
For people at higher risk of dangerous lows, such as older adults or those with a history of severe hypoglycemia, the targets are relaxed. The goal shifts to at least 50% of time in range, with less than 1% below 70 mg/dL. Avoiding dangerous lows takes priority over tightly controlling highs.
Blood Sugar Targets During Pregnancy
Pregnancy tightens the acceptable range significantly. Both the American College of Obstetricians and Gynecologists (ACOG) and the American Diabetes Association recommend that pregnant individuals keep fasting blood sugar below 95 mg/dL, with readings below 140 mg/dL one hour after meals or below 120 mg/dL two hours after meals. These stricter targets reduce the risk of the baby growing too large, which can complicate delivery.
For pregnant women with Type 1 diabetes using a CGM, the in-range target narrows to 63 to 140 mg/dL, with at least 70% of time spent in that window. The lower ceiling reflects how even moderately elevated blood sugar during pregnancy can affect fetal development.
Targets for Children and Teens
Children and adolescents with diabetes follow the same core CGM target of 70 to 180 mg/dL as adults, aiming for more than 70% time in range. When checking blood sugar with a finger prick, the recommended pre-meal target is 70 to 144 mg/dL, and the post-meal target is 70 to 180 mg/dL.
The recommended A1C goal for young people is 7% or below. For those using advanced technology like automated insulin delivery systems, a tighter target of 6.5% or below is recommended, as long as reaching it doesn’t increase the risk of severe lows or add stress that affects quality of life. Achieving that tighter A1C typically requires spending more than 80% of the day in range.
mg/dL vs. mmol/L
If you’ve seen blood sugar reported in different units depending on the country, the explanation is simple. The United States uses milligrams per deciliter (mg/dL), while most of the rest of the world uses millimoles per liter (mmol/L). To convert mg/dL to mmol/L, divide by 18. To go the other direction, multiply by 18. So a fasting reading of 100 mg/dL equals about 5.6 mmol/L, and the diabetes threshold of 126 mg/dL equals 7.0 mmol/L.