A normal fasting blood sugar level is below 100 mg/dL (5.6 mmol/L), and a normal reading two hours after eating is below 140 mg/dL (7.8 mmol/L). These are the standard benchmarks for adults without diabetes, though the numbers shift slightly depending on your age, when you last ate, and how the test is done.
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 most adults, a healthy result falls between 74 and 100 mg/dL. Once fasting levels climb to 100–125 mg/dL, that’s considered prediabetes. A reading of 126 mg/dL or higher on two separate tests meets the diagnostic threshold for diabetes.
Your body keeps blood sugar in this tight window through a balancing act between two hormones made by the pancreas. Insulin lowers blood sugar by shuttling glucose into your muscles, fat, and liver cells, where it’s either burned for energy or stored. Glucagon does the opposite: when blood sugar drops too low, it signals the liver to release stored glucose back into the bloodstream and even convert amino acids into fresh glucose. These two hormones work against each other constantly, like a thermostat, to keep levels stable.
After-Meal Blood Sugar
Blood sugar naturally rises after you eat. It typically peaks one to two hours after your first bite, then gradually returns to baseline as insulin clears the glucose from your bloodstream. In a person without diabetes, that peak stays below 140 mg/dL. The American Diabetes Association recommends checking post-meal levels one to two hours after eating, and for people managing diabetes, a general target is to stay under 180 mg/dL at that mark.
What you eat matters. A meal heavy in refined carbohydrates (white bread, sugary drinks, white rice) will spike your blood sugar faster and higher than a meal built around protein, fiber, and healthy fats. The speed of digestion, the amount of fiber slowing glucose absorption, and even the order in which you eat different foods on your plate all influence how high that post-meal peak goes and how quickly it comes back down.
HbA1c: The Bigger Picture
While fasting and post-meal readings capture a single moment, the HbA1c test reflects your average blood sugar over the previous 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 gets stuck to hemoglobin.
The thresholds are straightforward:
- Normal: below 5.7%
- Prediabetes: 5.7% to 6.4%
- Diabetes: 6.5% or higher
An HbA1c of 5.7% corresponds to an average blood sugar of roughly 117 mg/dL. Because it smooths out the daily ups and downs, this test is especially useful for spotting a pattern of gradually rising blood sugar that individual fasting readings might miss.
How Ranges Change With Age
Children and older adults don’t share the same targets. In children under two, normal blood sugar runs between 60 and 100 mg/dL, while infants can be healthy at levels as low as 40 mg/dL, a number that would cause symptoms in an adult.
On the other end of the spectrum, adults over 60 tend to run slightly higher. Fasting levels up to 110–120 mg/dL and post-meal readings up to 150 mg/dL are often considered acceptable for seniors. This shift happens because insulin sensitivity naturally decreases with age, and the body’s metabolic machinery slows. There’s also a practical reason for looser targets in older adults: the risk of hypoglycemia (dangerously low blood sugar) increases with age, and the consequences of a severe low, including falls, confusion, and cardiac events, can be more harmful than running slightly above the textbook range.
When Blood Sugar Drops Too Low
Blood sugar below 70 mg/dL is classified as hypoglycemia. Early warning signs include sweating, a racing heartbeat, sudden anxiety, flushed skin, and intense hunger. These are your body’s alarm signals, driven by a surge of stress hormones trying to push glucose back up.
If levels keep falling, symptoms escalate to headaches, dizziness, confusion, difficulty speaking, and in severe cases, seizures or loss of consciousness. Hypoglycemia is most common in people taking insulin or certain diabetes medications, but it can also happen after prolonged fasting, intense exercise, or excessive alcohol intake in people without diabetes.
The Oral Glucose Tolerance Test
If a standard fasting test comes back borderline, your doctor may order an oral glucose tolerance test (OGTT). You drink a liquid containing 75 grams of glucose (roughly the sugar in two cans of soda), and your blood is drawn two hours later. A result below 140 mg/dL is normal, 140–199 mg/dL indicates prediabetes, and 200 mg/dL or above points to diabetes.
Pregnant women undergo a version of this test to screen for gestational diabetes, though the protocol and cutoffs differ. The follow-up test for gestational diabetes uses a larger glucose dose and measures blood sugar at one, two, and three hours. Expected values are 180 mg/dL or lower at the one-hour mark and 155 mg/dL or lower at two hours.
What Affects Your Numbers Day to Day
Blood sugar isn’t static. Even in a perfectly healthy person, it fluctuates throughout the day based on dozens of variables. Sleep quality, stress, physical activity, hydration, illness, and hormonal cycles all push your numbers around. Cortisol, the body’s primary stress hormone, directly triggers the liver to release stored glucose, which is why a rough night of sleep or a stressful morning can show up as a higher fasting reading even if you ate well the day before.
Exercise typically lowers blood sugar by making your muscles absorb glucose more efficiently, sometimes for up to 24 hours afterward. But very intense exercise, like sprinting or heavy weightlifting, can temporarily raise blood sugar because stress hormones spike during the effort. Neither scenario is cause for concern. The body corrects both within a few hours.
If you’re monitoring at home with a finger-stick glucose meter, keep in mind that these devices have a margin of error of about 15%. A reading of 105 mg/dL could realistically be anywhere from 89 to 121. One slightly elevated number in isolation tells you very little. The pattern across multiple readings, and especially the HbA1c, gives a much more reliable picture.