For a healthy adult who hasn’t eaten in at least eight hours, blood sugar should fall between roughly 70 and 99 mg/dL. After a meal, it normally stays below 140 mg/dL. These numbers shift depending on your age, whether you’re pregnant, and what you’ve just eaten, so the full picture is more nuanced than a single range.
Fasting Blood Sugar
Fasting blood sugar is measured after at least eight hours without food, usually first thing in the morning. A reading under 100 mg/dL is considered normal. Between 100 and 125 mg/dL falls into the prediabetes range, signaling that your body is starting to have trouble processing sugar efficiently. A fasting level of 126 mg/dL or higher on two separate tests is used to diagnose diabetes.
For people without diabetes, readings below 70 mg/dL count as low blood sugar. That threshold matters because symptoms like shakiness, sweating, dizziness, and confusion tend to kick in around that point. A drop below 54 mg/dL is considered severe and can cause weakness, trouble walking, seizures, or loss of consciousness.
Blood Sugar After Eating
Your blood sugar naturally rises after a meal, peaking somewhere around 30 to 60 minutes after you start eating and then gradually dropping back down. In a healthy person, it should return to below 140 mg/dL within two hours of eating. For someone with diabetes, levels above 180 mg/dL at that point are generally considered too high.
What you eat matters more than you might expect. A Stanford Medicine study that fitted 57 people with continuous glucose monitors for about two weeks found striking results: more than half of participants whose prior blood tests classified them as “healthy” spiked into prediabetic or diabetic territory after certain meals. Eighty percent of participants spiked after eating a bowl of cornflakes with milk. The type of carbohydrate you consume, not just the amount, plays a significant role in how high your blood sugar climbs.
A1C: The Bigger Picture
While a finger-stick reading captures a single moment, the A1C test reflects your average blood sugar over the past two to three months. It measures the percentage of your red blood cells that have sugar attached to them, giving a much broader view of how well your body manages glucose day to day.
The CDC uses these thresholds:
- Normal: below 5.7%
- Prediabetes: 5.7% to 6.4%
- Diabetes: 6.5% or above
If you already have diabetes, the general target is keeping your A1C under 7%, though your doctor may set a more or less aggressive goal depending on your situation.
Targets During Pregnancy
Blood sugar targets are tighter during pregnancy because elevated glucose can affect both the mother and the developing baby. The American College of Obstetricians and Gynecologists recommends these goals for pregnant women:
- Fasting: below 95 mg/dL
- One hour after eating: below 140 mg/dL
- Two hours after eating: below 120 mg/dL
These numbers apply whether you had diabetes before pregnancy or developed gestational diabetes during it. Most pregnant women are asked to check their blood sugar several times a day to stay within these ranges.
Targets for Children and Teens
Children with diabetes have slightly wider target ranges than adults because tight blood sugar control carries a higher risk of dangerous lows in younger kids. The American Diabetes Association sets age-specific goals:
- Ages 0 to 6: 100 to 200 mg/dL, with an A1C between 7.5% and 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%
As children grow and become better able to recognize and respond to low blood sugar on their own, the targets gradually narrow toward adult ranges.
What Happens When Blood Sugar Stays Too High
A single spike after a big meal isn’t dangerous on its own. The concern is chronically elevated blood sugar, which slowly damages blood vessels and nerves throughout the body. Over years, sustained high glucose can lead to vision problems from damage to the blood vessels in the eyes, kidney disease, nerve damage that causes numbness or pain (especially in the feet and hands), digestive issues from impaired nerve function in the gut, and a significantly increased risk of heart disease and stroke.
For someone without a diabetes diagnosis, a fasting level above 125 mg/dL is the threshold for hyperglycemia. Many people with consistently elevated blood sugar don’t feel any symptoms until levels are quite high, which is why routine screening matters. Prediabetes in particular is often silent, affecting an estimated one in three American adults, most of whom don’t know they have it.
How Blood Sugar Naturally Fluctuates
Blood sugar is not a fixed number. It rises and falls throughout the day in response to meals, physical activity, stress, sleep quality, and even the time of day. Morning readings tend to be slightly higher than you’d expect because the liver releases stored sugar overnight to keep your brain fueled while you sleep. This is sometimes called the “dawn phenomenon.”
Exercise pulls sugar out of your bloodstream and into your muscles for fuel, which is why a walk after eating can noticeably blunt a post-meal spike. Stress and illness raise blood sugar through the release of hormones like cortisol and adrenaline, even if you haven’t eaten anything unusual. Understanding these patterns helps explain why two readings taken on the same day can look quite different, and why a single test is never the whole story.