A good blood sugar number for a healthy adult is between 70 and 99 mg/dL when measured after fasting (no food for at least 8 hours). After eating, blood sugar naturally rises but should stay below 140 mg/dL within two hours of a meal. These two numbers give you the clearest snapshot of where you stand, but the full picture depends on when you’re testing, whether you’re pregnant, and whether you’re managing diabetes.
Fasting Blood Sugar: Your Baseline Number
Fasting blood sugar is the most common measurement and the one your doctor orders during routine bloodwork. It’s taken after you haven’t eaten for at least 8 hours, usually first thing in the morning. The ranges break down cleanly:
- Normal: below 100 mg/dL
- Prediabetes: 100 to 125 mg/dL
- Diabetes: 126 mg/dL or higher
If your fasting number lands between 70 and 99 mg/dL, your body is processing glucose well. A result in the 100 to 125 range means your cells are becoming resistant to insulin, the hormone that moves sugar out of your blood and into your cells. This is prediabetes, and it’s reversible with lifestyle changes. A fasting level of 126 or above, confirmed on two separate tests, meets the diagnostic threshold for diabetes.
After-Meal Blood Sugar
Blood sugar peaks roughly 1 to 2 hours after you start eating. In a healthy person, that peak stays below 140 mg/dL and returns close to your fasting level within a few hours. If you’re checking at home, testing about two hours after your first bite gives you the most useful reading.
What you eat matters enormously for this number. 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. Two people with the same fasting number can have very different post-meal responses depending on what’s on their plate.
A1C: The Three-Month Average
While fasting and post-meal readings are snapshots, the A1C test measures your average blood sugar over the previous two to three months. It works by measuring how much sugar has attached to your red blood cells, which live about 90 days. The result is reported as a percentage:
- Normal: below 5.7%
- Prediabetes: 5.7% to 6.4%
- Diabetes: 6.5% or higher
Each percentage point translates to a specific average blood sugar level. An A1C of 6% corresponds to an average of about 126 mg/dL. At 7%, the average jumps to roughly 154 mg/dL. At 8%, it’s around 183 mg/dL. For people managing diabetes, most guidelines recommend keeping A1C below 7%, though your personal target may differ based on age, other health conditions, and how long you’ve had diabetes.
The A1C is especially useful because it smooths out the daily fluctuations. You might have a great fasting number on the morning of your blood draw but consistently spike after meals. The A1C catches that pattern.
Targets During Pregnancy
Pregnancy tightens the acceptable ranges considerably because high blood sugar can affect fetal development. The American College of Obstetricians and Gynecologists recommends these targets for pregnant women with diabetes:
- Fasting: below 95 mg/dL
- 1 hour after eating: below 140 mg/dL
- 2 hours after eating: below 120 mg/dL
- A1C: no higher than 6%
These targets are lower than the general diabetes goals because even moderately elevated blood sugar during pregnancy increases the risk of complications. Women with gestational diabetes typically check their blood sugar four or more times per day to stay within these tighter windows.
When Blood Sugar Drops Too Low
Low blood sugar (hypoglycemia) is primarily a concern for people taking insulin or certain diabetes medications, but it’s worth understanding the thresholds. Below 70 mg/dL is considered mild hypoglycemia. You might feel shaky, sweaty, irritable, or suddenly hungry. Below 54 mg/dL is moderate hypoglycemia and requires immediate attention, typically fast-acting sugar like juice or glucose tablets. Severe hypoglycemia can cause confusion, seizures, or loss of consciousness and requires someone else’s help.
For people without diabetes, the body is very good at preventing blood sugar from dropping dangerously low. The liver releases stored glucose, and the pancreas dials back insulin production. This self-correcting system keeps most people safely above 70 mg/dL even during long gaps between meals.
Why Morning Numbers Can Be Higher Than Expected
If you have diabetes and notice your fasting blood sugar is unexpectedly high despite eating well the night before, the likely culprit is a process called the dawn phenomenon. Between roughly 3 a.m. and 8 a.m., your body releases a surge of cortisol and growth hormone that signals your liver to produce more glucose. This is a normal wake-up mechanism. In people without diabetes, the pancreas compensates by releasing more insulin. In people with diabetes, the insulin response is insufficient, so blood sugar rises overnight and is already elevated by morning.
This can be frustrating because it’s not caused by anything you ate. Adjusting medication timing, evening meals, or physical activity patterns can help, but it’s something to discuss with your care team rather than troubleshoot alone.
Continuous Glucose Monitors and Time in Range
Continuous glucose monitors (CGMs) have shifted how many people think about blood sugar. Instead of isolated finger-stick readings, a CGM tracks your glucose every few minutes throughout the day and night. This creates a new metric called “time in range,” which measures what percentage of the day your blood sugar stays between 70 and 180 mg/dL.
The goal for most people with diabetes is to spend at least 70% of the day in that range, which works out to roughly 17 out of 24 hours. This metric captures something A1C and spot checks can miss: how stable your blood sugar is throughout the day. Two people can have the same A1C, but one might have smooth, steady glucose levels while the other swings dramatically between highs and lows. Time in range reveals that difference.
Converting Between Units
If you’re reading blood sugar information from outside the United States, you’ll encounter a different unit: mmol/L instead of mg/dL. The conversion is straightforward. Divide mg/dL by 18 to get mmol/L, or multiply mmol/L by 18 to get mg/dL. So a fasting reading of 90 mg/dL equals 5.0 mmol/L, and the diabetes threshold of 126 mg/dL equals 7.0 mmol/L. The numbers look very different, but they describe the same thing.