Your sugar level, or blood glucose level, is the concentration of glucose circulating in your bloodstream at any given moment. For a healthy adult without diabetes, a normal fasting blood sugar falls between 70 and 99 mg/dL. That number shifts throughout the day based on what you eat, how active you are, your stress levels, and even how well you slept the night before.
How Your Body Regulates Blood Sugar
Glucose is your body’s primary fuel. When you eat carbohydrates, your digestive system breaks them down into glucose, which enters your bloodstream. Your pancreas then releases insulin, a hormone that acts like a key, unlocking your muscle, fat, and liver cells so they can absorb that glucose and either use it for energy or store it for later.
Between meals and overnight, a second hormone called glucagon takes over. Glucagon signals your liver to break down its stored glucose (called glycogen) and release it back into the bloodstream so your brain, organs, and muscles stay fueled even when you haven’t eaten in hours. This back-and-forth between insulin and glucagon keeps your blood sugar in a remarkably tight range all day long, as long as both systems are working properly.
Normal Blood Sugar Ranges
The numbers below apply to adults who are not pregnant. All values are measured in milligrams per deciliter (mg/dL), the standard unit used in the United States.
Fasting (no food for at least 8 hours): 70 to 99 mg/dL is considered normal. Some people without diabetes can dip to 50 to 70 mg/dL and still be perfectly healthy, though values below 70 generally warrant attention.
Two hours after eating: Blood sugar naturally rises after a meal. For most people, it should come back down to less than 140 mg/dL within two hours. For people already managing diabetes, a reading under 180 mg/dL at the two-hour mark is the typical target.
A1C (a three-month average): Unlike a single finger-stick reading, the A1C test reflects your average blood sugar over roughly the past two to three months. A normal A1C is below 5.7%.
Prediabetes and Diabetes Thresholds
Blood sugar doesn’t jump from normal to diabetic overnight. There’s a middle zone called prediabetes, where levels are elevated but not yet high enough for a diabetes diagnosis. Recognizing this range matters because lifestyle changes at this stage can slow or even reverse the progression.
- Prediabetes: Fasting glucose of 100 to 125 mg/dL, or an A1C of 5.7% to 6.4%, or a two-hour glucose tolerance result of 140 to 199 mg/dL.
- Diabetes: Fasting glucose of 126 mg/dL or higher, or an A1C of 6.5% or above, or a two-hour glucose tolerance result of 200 mg/dL or higher. A random blood sugar reading of 200 mg/dL or above with classic symptoms (excessive thirst, frequent urination, unexplained weight loss) also qualifies.
Doctors typically require two abnormal test results, either from the same blood draw or on separate occasions, before confirming a diabetes diagnosis. A single high reading alone isn’t enough.
When Blood Sugar Drops Too Low
Low blood sugar, called hypoglycemia, is generally defined as a reading below 70 mg/dL. It’s most common in people who take insulin or certain diabetes medications, but it can happen to anyone who skips meals or exercises intensely without eating.
The warning signs come on quickly: shakiness, dizziness, sudden hunger, a racing heartbeat, confusion, and irritability. You might have trouble seeing or speaking clearly. If levels drop very low and aren’t corrected with fast-acting carbohydrates (juice, glucose tablets, regular soda), it can lead to loss of consciousness or seizures. This is one of the few blood sugar situations that qualifies as a genuine emergency.
When Blood Sugar Runs Too High
High blood sugar, or hyperglycemia, often produces no noticeable symptoms until readings climb above 180 to 200 mg/dL. At that point you might notice frequent urination, increased thirst, blurred vision, and unusual fatigue. These symptoms develop because your kidneys start trying to flush the excess glucose out through urine, pulling water along with it and leaving you dehydrated.
Sustained high readings over weeks and months are what cause the long-term complications associated with diabetes: nerve damage, kidney problems, and vision loss. In extreme cases, blood sugar can spike above 600 mg/dL, a dangerous condition that requires emergency treatment.
Surprising Factors That Affect Your Levels
Food is the most obvious influence on blood sugar, but it’s far from the only one. Stress of any kind, whether emotional or physical (even a sunburn), triggers your body to release hormones that push glucose into your bloodstream. Losing just one night of sleep can make your cells respond less effectively to insulin the next day.
Dehydration concentrates the glucose already in your blood, giving you a higher reading even though the total amount of sugar hasn’t changed. Time of day also plays a role: most people experience a natural hormone surge in the early morning hours (sometimes called the dawn phenomenon) that nudges fasting levels slightly higher. Even gum disease has been linked to elevated blood sugar, creating a two-way relationship where high glucose worsens gum health and inflamed gums make blood sugar harder to control.
How Blood Sugar Is Tested
There are several ways to measure your sugar level, and each one captures a slightly different picture.
A fasting blood glucose test is the most straightforward. You fast for at least eight hours (usually overnight), then have blood drawn. It tells you what your baseline level looks like when food isn’t a factor.
An oral glucose tolerance test measures how well your body handles a sugar load. You drink a standardized glucose solution, then have your blood tested two hours later. This test is especially useful for catching prediabetes that a fasting test might miss.
The A1C test doesn’t require fasting. It measures the percentage of your red blood cells that have glucose attached to them. Because red blood cells live about three months, this gives a reliable average. It’s the test most often used for ongoing diabetes management.
A random blood glucose test can be taken at any time regardless of when you last ate. It’s typically used when symptoms are obvious and a quick confirmation is needed. A result of 200 mg/dL or above with symptoms points strongly toward diabetes.
For people who monitor daily, continuous glucose monitors (small sensors worn on the skin) track levels in real time and report a metric called Time in Range. The goal for most adults with diabetes is spending more than 70% of the day between 70 and 180 mg/dL, with less than 4% of the day below 70 mg/dL.