For a healthy adult, normal blood sugar is 99 mg/dL or below after fasting and under 140 mg/dL two hours after eating. These two numbers are the standard benchmarks doctors use to assess whether your body is managing glucose properly. Your blood sugar doesn’t stay fixed at one number, though. It rises and falls throughout the day depending on what you eat, how active you are, and even how well you slept.
Fasting Blood Sugar: Your Baseline Number
Fasting blood sugar is measured after at least eight hours without food, typically first thing in the morning. A reading of 99 mg/dL or below is considered normal. Once you hit 100 to 125 mg/dL, you’re in the prediabetes range. A fasting level of 126 mg/dL or higher on two separate tests indicates diabetes.
This fasting number matters because it reflects how well your body regulates glucose on its own, without the influence of a recent meal. When everything is working properly, your pancreas releases a hormone called glucagon between meals and overnight. Glucagon signals your liver to release stored glucose into your bloodstream, keeping levels steady while you sleep. A normal fasting reading means that system is functioning well.
After Eating: What to Expect
Blood sugar naturally rises after you eat. Your body breaks carbohydrates down into glucose, which enters the bloodstream and triggers insulin release from the pancreas. Insulin acts like a key, unlocking muscle and fat cells so they can absorb that glucose and use it for energy. In a healthy person, this process brings blood sugar back down relatively quickly.
Two hours after a meal, a normal reading is under 140 mg/dL. If your blood sugar is still above 140 at the two-hour mark, it could signal that your body isn’t clearing glucose efficiently. A reading between 140 and 199 mg/dL at this point falls into the prediabetes category, and 200 mg/dL or above points toward diabetes.
The A1C Test: A Longer View
While fasting and post-meal readings capture a single moment, the A1C test measures your average blood sugar over the previous two to three months. It works by measuring the percentage of your red blood cells that have glucose attached to them. The higher your blood sugar has been running, the higher that percentage.
A normal A1C is below 5.7%. An A1C between 5.7% and 6.4% indicates prediabetes, and within that range, higher numbers carry greater risk. An A1C of 6.5% or above on two separate tests means diabetes. Because the A1C reflects a long-term average rather than a snapshot, it’s useful for catching patterns that a single fasting test might miss.
When Blood Sugar Drops Too Low
Most people focus on high blood sugar, but low blood sugar (hypoglycemia) matters too. A reading below 70 mg/dL is considered low and can cause shakiness, sweating, dizziness, and irritability. Below 54 mg/dL, symptoms become more serious: confusion, blurred vision, and in rare cases, seizures. Low blood sugar is more common in people taking diabetes medication, but it can happen in anyone who skips meals, exercises intensely without eating, or drinks alcohol on an empty stomach.
Normal Ranges During Pregnancy
Pregnancy shifts blood sugar targets downward. A normal fasting level for a pregnant woman is below 95 mg/dL, slightly stricter than the general 99 mg/dL cutoff. One hour after eating, the target is under 180 mg/dL, and at two hours it should drop below 155 mg/dL. These tighter thresholds exist because elevated blood sugar during pregnancy increases the risk of complications for both mother and baby, even at levels that would be considered borderline outside of pregnancy.
Normal Ranges for Children
Children with diabetes have different targets than adults, reflecting the challenges of managing blood sugar in growing bodies. The American Diabetes Association sets these age-based goals for children who are managing diabetes:
- 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 ranges are wider than adult targets because young children are more vulnerable to low blood sugar episodes, and tighter control can sometimes do more harm than good at certain developmental stages.
Why Your Numbers Fluctuate
Blood sugar is not static. Even in a perfectly healthy person, levels shift throughout the day. Several everyday factors drive those fluctuations:
- Food choices: Meals high in refined carbohydrates cause a faster, steeper rise than meals with more protein, fat, and fiber.
- Physical activity: Exercise pulls glucose into your muscles for fuel, which lowers blood sugar. This effect can last for hours after a workout.
- Stress: Physical or emotional stress triggers hormone release that pushes blood sugar up. This includes both negative stress and positive excitement.
- Sleep: Poor sleep can reduce your body’s sensitivity to insulin, leading to higher morning readings.
- Dehydration: When you’re dehydrated, the glucose in your blood becomes more concentrated, which can push readings higher.
- Illness or infection: Your body releases stress hormones when fighting off a cold or infection, which often raises blood sugar temporarily.
How Your Body Keeps Blood Sugar Stable
Your pancreas is the control center. It produces two hormones that work in opposition to keep blood sugar within a tight range. After you eat and blood sugar rises, your pancreas releases insulin, which moves glucose out of the bloodstream and into your cells. Between meals or during sleep, when blood sugar starts to dip, the pancreas releases glucagon instead. Glucagon tells your liver to convert its stored glycogen back into glucose and release it into the blood.
This back-and-forth between insulin and glucagon keeps healthy blood sugar in a remarkably narrow window. Your liver plays a central role as the storage facility, banking glucose when there’s excess and releasing it when supplies run low. Problems with blood sugar regulation typically begin when cells stop responding to insulin as effectively, a condition called insulin resistance, which is the hallmark of prediabetes and type 2 diabetes.
Quick Reference: Blood Sugar Ranges
- Normal fasting: 99 mg/dL or below
- Prediabetes fasting: 100 to 125 mg/dL
- Diabetes fasting: 126 mg/dL or above
- Normal 2 hours after eating: under 140 mg/dL
- Low blood sugar: below 70 mg/dL
- Normal A1C: below 5.7%
- Prediabetes A1C: 5.7% to 6.4%
- Diabetes A1C: 6.5% or above