A normal fasting blood sugar reading is below 100 mg/dL (5.6 mmol/L). After eating, blood sugar rises temporarily but should drop back below 140 mg/dL within two hours. These two numbers are the benchmarks most people need to know.
Fasting Blood Sugar
Fasting blood sugar is measured after you haven’t eaten for at least eight hours, typically first thing in the morning. For a healthy adult, the normal range is below 100 mg/dL. A reading between 100 and 125 mg/dL falls into the prediabetes zone, sometimes called impaired fasting glucose. At 126 mg/dL or higher on two separate tests, the reading meets the threshold for diabetes.
It’s worth noting that “normal” doesn’t mean your fasting sugar sits at exactly one number every day. In a large study of over 4,800 people without diabetes who wore continuous glucose monitors, the average fasting reading was 91 mg/dL, with natural variation of about 10 points in either direction. So a reading of 85 one morning and 95 the next is perfectly typical.
Blood Sugar After Meals
Your blood sugar always rises after you eat. That’s expected. The question is how high it goes and how quickly it comes back down. For someone without diabetes, blood sugar should return to below 140 mg/dL within two hours of eating. If it stays above that mark at the two-hour point, that’s a sign your body may not be processing glucose efficiently.
In practice, most healthy people peak somewhere between 120 and 140 mg/dL about 30 to 60 minutes after a meal, then steadily decline. The size of that spike depends heavily on what you ate. A bowl of white rice will push blood sugar higher and faster than a plate of chicken and vegetables. This is one reason post-meal readings can vary so much from day to day, even for the same person.
The HbA1c Test
While a finger prick or lab draw captures your blood sugar at a single moment, the HbA1c test shows your average blood sugar over the previous two to three months. It works by measuring the percentage of hemoglobin (a protein in red blood cells) that has glucose attached to it. The more glucose circulating in your blood over time, the higher that percentage climbs.
The CDC uses these cutoffs:
- Normal: below 5.7%
- Prediabetes: 5.7% to 6.4%
- Diabetes: 6.5% or above
An HbA1c of 5.7% roughly translates to an average blood sugar of about 117 mg/dL. This test is especially useful because it isn’t affected by what you ate that morning or whether you remembered to fast. It reflects the bigger picture.
Normal Ranges During Pregnancy
Pregnancy tightens the goalposts. Hormonal changes during the second and third trimesters can make it harder for insulin to do its job, which is why gestational diabetes screening happens around weeks 24 to 28. Both the American College of Obstetricians and Gynecologists and the American Diabetes Association recommend these targets for pregnant women:
- Fasting: below 95 mg/dL
- One hour after eating: below 140 mg/dL
- Two hours after eating: below 120 mg/dL
The post-meal clock starts from the beginning of the meal, not the end. That distinction matters because a 45-minute dinner pushes your one-hour check close to the two-hour window if you time it from when you finished instead.
Normal Ranges for Children
Children’s normal blood sugar ranges are slightly different from adults, particularly in the first years of life. For newborns, normal glucose can be as low as 30 to 60 mg/dL, which would be considered dangerously low in an adult. Infants typically range from 40 to 90 mg/dL. By age two, the reference range is 60 to 100 mg/dL, essentially matching the adult range. After that point, the same thresholds used for adults apply.
mg/dL vs. mmol/L
If you’ve ever seen blood sugar written as “5.5” instead of “100,” you’re looking at a different unit of measurement. The United States and much of continental Europe use mg/dL (milligrams per deciliter). The UK, Canada, Australia, and many other countries use mmol/L (millimoles per liter). To convert between them, divide mg/dL by 18 to get mmol/L, or multiply mmol/L by 18 to get mg/dL.
Here’s what the key thresholds look like in both units:
- Normal fasting: below 100 mg/dL / below 5.6 mmol/L
- Prediabetes fasting: 100 to 125 mg/dL / 5.6 to 6.9 mmol/L
- Diabetes fasting: 126 mg/dL or above / 7.0 mmol/L or above
- Normal after meals (2 hours): below 140 mg/dL / below 7.8 mmol/L
What Continuous Glucose Monitors Reveal
Continuous glucose monitors (CGMs) have given researchers a much more detailed picture of what “normal” blood sugar actually looks like throughout the day. Instead of a single snapshot, these sensors take a reading every few minutes. In healthy, non-diabetic adults, the data shows that blood sugar stays between 70 and 140 mg/dL about 91% of the time. When researchers used a tighter range of 70 to 100 mg/dL, time in range dropped to around 70%.
That means even people with perfectly healthy metabolism spend a meaningful portion of the day above 100 mg/dL, mostly after meals. Occasional spikes into the 120s or 130s after eating are completely normal and not a sign of a problem. What matters is that blood sugar returns to baseline within a couple of hours and doesn’t stay elevated.
Prediabetes: The In-Between Zone
The gap between “normal” and “diabetes” isn’t empty. Prediabetes means your blood sugar is higher than normal but hasn’t crossed the diabetes threshold. It can show up in different ways. Some people have elevated fasting numbers (100 to 125 mg/dL) but handle meals fine. Others have normal fasting readings but their blood sugar climbs too high after eating, staying between 140 and 199 mg/dL at the two-hour mark on a glucose tolerance test. These two patterns are called impaired fasting glucose and impaired glucose tolerance, and you can have one or both.
Prediabetes affects a large portion of the population, and many people don’t know they have it because it rarely causes symptoms. The practical importance is that it’s reversible. Losing 5 to 7% of your body weight and adding regular physical activity can bring numbers back into the normal range for many people. That’s roughly 10 to 14 pounds for someone who weighs 200 pounds.