For a healthy adult, normal fasting blood sugar falls between about 70 and 99 mg/dL. Two hours after eating, it should stay below 140 mg/dL. These are the numbers most people encounter on lab results, but blood sugar isn’t one static number. It shifts throughout the day based on what you eat, how you move, and even how well you slept.
Fasting Blood Sugar
Fasting blood sugar is measured after you haven’t eaten for at least eight hours, typically first thing in the morning. In people without diabetes, fasting glucose stays in a tight range of about 79 to 90 mg/dL. A result under 100 mg/dL is considered normal. Between 100 and 125 mg/dL falls into the prediabetes range, and 126 mg/dL or higher on two separate tests points toward diabetes.
These thresholds matter because fasting glucose reflects your body’s baseline ability to regulate sugar when no food is coming in. If your fasting number creeps above 100, your body is likely having trouble clearing glucose from the bloodstream overnight, which is one of the earliest signs of insulin resistance.
After-Meal Blood Sugar
Blood sugar naturally rises after you eat. In a healthy person, it peaks about one hour after a meal and returns to baseline within two to three hours. At the two-hour mark, a reading below 140 mg/dL is normal. A result between 140 and 199 mg/dL suggests prediabetes, and 200 mg/dL or above indicates diabetes.
Continuous glucose monitors have given researchers a much clearer picture of what happens between meals in people without diabetes. In a multicenter study tracking healthy participants around the clock, people spent a median of 96% of their time with blood sugar between 70 and 140 mg/dL. That means even in completely healthy people, brief spikes above 140 can happen, particularly after high-carb meals. The key is how quickly blood sugar comes back down.
The A1C Test
While fasting and post-meal readings capture a single moment, the A1C test reflects 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 more glucose sticks to those cells.
- Normal: below 5.7%
- Prediabetes: 5.7% to 6.4%
- Diabetes: 6.5% or above
A1C is useful because it isn’t affected by what you ate yesterday or whether you fasted before the blood draw. It gives a broader picture of how well your body has been managing glucose over time. A normal A1C of 5.0%, for example, corresponds to an average blood sugar of roughly 97 mg/dL.
When Blood Sugar Drops Too Low
The floor matters as much as the ceiling. Blood sugar below 70 mg/dL is considered low, a condition called hypoglycemia. At that level you might feel shaky, sweaty, irritable, or suddenly hungry. Below 54 mg/dL is classified as severe, and symptoms escalate to confusion, difficulty walking, blurred vision, and in some cases fainting or seizures.
Hypoglycemia is most common in people taking insulin or certain diabetes medications, but it can also happen after prolonged fasting, intense exercise, or heavy alcohol consumption in people without diabetes. If you notice these symptoms, eating 15 to 20 grams of fast-acting carbohydrates (a few glucose tablets, half a cup of juice) typically brings levels back up within 15 minutes.
How Targets Change During Pregnancy
Pregnancy tightens the window for what’s considered safe. Blood sugar that would be perfectly normal outside of pregnancy can affect fetal growth, so the targets drop. For pregnant women being monitored for gestational diabetes, the standard clinical targets are a fasting level of 95 mg/dL or below, under 140 mg/dL at one hour after meals, and under 120 mg/dL at two hours.
In practice, healthy pregnant women without diabetes run even lower than those targets. Research pooling data from nearly 200 pregnancies found an average fasting glucose of about 71 mg/dL, well below the 95 mg/dL cutoff used for gestational diabetes screening. This is partly because the growing placenta draws glucose from the mother’s bloodstream continuously, pulling fasting levels down.
Targets for Children
Children’s blood sugar targets are slightly wider than those of adults, largely because young kids are less able to recognize and communicate symptoms of low blood sugar. General pediatric goals look like this:
- Under 5 years: 80 to 200 mg/dL
- Ages 5 to 11: 70 to 180 mg/dL
- Ages 12 and up: 70 to 150 mg/dL
These ranges apply mainly to children with diabetes who are monitoring their blood sugar throughout the day. A healthy child without diabetes will typically stay within the same adult range of 70 to 140 mg/dL, but the wider targets give a safety cushion for kids on insulin whose levels are harder to control precisely.
Targets for Older Adults
For older adults with diabetes, guidelines loosen rather than tighten. The reason is practical: aggressive blood sugar lowering in someone who is 75 or 80 increases the risk of dangerous hypoglycemic episodes, which can cause falls, confusion, and hospitalization. The benefits of very tight control, which mostly involve preventing complications 10 or 15 years down the road, may not outweigh those immediate risks.
For healthy older adults with a life expectancy of more than 10 years, an A1C below 7.5% is a reasonable goal, with fasting readings between 140 and 150 mg/dL. For frail older adults with multiple health conditions or shorter life expectancy, the target relaxes further to an A1C of 8% or below, with fasting glucose between 160 and 170 mg/dL. These aren’t numbers that would be “normal” in a younger, healthy person, but they represent the safest balance of risks for that population.
What Makes Blood Sugar Fluctuate
Even in perfectly healthy people, blood sugar is never a flat line. A large bowl of white rice will spike your glucose more than a plate of grilled chicken and vegetables. Exercise generally lowers blood sugar by helping muscles absorb glucose without needing as much insulin, though very intense or prolonged exercise can temporarily raise it due to stress hormones.
Sleep deprivation, physical illness, stress, and certain medications (like steroids) can all push fasting glucose higher without any change in diet. Dehydration concentrates glucose in the blood, which can produce a falsely elevated reading. If a single test comes back higher than expected, your doctor will typically repeat it before drawing conclusions. One reading is a data point. A pattern is a diagnosis.