A normal fasting blood sugar level for a healthy adult is 70 to 99 mg/dL (3.9 to 5.5 mmol/L). That’s the number you’d see on a blood test taken first thing in the morning before eating. But “normal” shifts depending on when you last ate, your age, and whether you’re pregnant, so the full picture involves several different numbers.
Normal 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 adults without diabetes, the healthy range is 70 to 99 mg/dL. Some people naturally sit between 50 and 70 mg/dL without any symptoms or problems, which is also considered normal.
Once fasting glucose hits 100 to 125 mg/dL, it falls into the prediabetes range. At 126 mg/dL or above on two separate tests, it meets the threshold for a diabetes diagnosis. These cutoffs matter because they’re the numbers your doctor uses to decide whether further testing is needed.
Blood Sugar After Eating
Your blood sugar naturally rises after a meal and then comes back down as insulin moves glucose into your cells. In a person without diabetes, blood sugar typically peaks about 60 to 90 minutes after eating and returns close to baseline within two to three hours. At the two-hour mark, a normal reading is below 140 mg/dL (7.8 mmol/L).
If your two-hour post-meal reading lands between 140 and 199 mg/dL, that suggests impaired glucose tolerance, a hallmark of prediabetes. A result of 200 mg/dL or higher points toward diabetes.
HbA1c: Your Three-Month Average
While a single blood sugar reading captures one moment, the HbA1c test reflects your average blood sugar over the past two to three months. It measures the percentage of your red blood cells that have glucose attached to them. The CDC uses these thresholds:
- Normal: below 5.7%
- Prediabetes: 5.7% to 6.4%
- Diabetes: 6.5% or above
An HbA1c of 5.7% translates to an average blood sugar of roughly 117 mg/dL. This test is useful because it isn’t thrown off by what you ate yesterday or how well you slept. It gives a broader view of how your body handles sugar over time.
What Continuous Monitors Show
Continuous glucose monitors (CGMs) give the most detailed picture of blood sugar throughout the day. A 2024 study in the Journal of Clinical Endocrinology & Metabolism tracked over 500 adults without diabetes wearing CGMs and found they spent about 87% of their time in the 70 to 140 mg/dL range. That means even healthy people spend some portion of the day above 140, particularly right after carb-heavy meals, and occasionally dip below 70 during sleep or exercise.
This is worth knowing because a single reading of 145 mg/dL an hour after lunch doesn’t automatically signal a problem. Blood sugar is a moving target, not a fixed number.
Normal Ranges During Pregnancy
Pregnancy tightens the targets. Hormonal changes naturally increase insulin resistance, which is why doctors screen for gestational diabetes between 24 and 28 weeks. The recommended targets for pregnant women, set by both the American College of Obstetricians and Gynecologists and the American Diabetes Association, are:
- Fasting: below 95 mg/dL
- One hour after a meal: below 140 mg/dL
- Two hours after a meal: below 120 mg/dL
Post-meal timing starts from the beginning of the meal, not when you finish eating. These numbers are stricter than the general population targets because elevated blood sugar during pregnancy carries risks for both the mother and baby.
Normal Ranges for Children
Children’s blood sugar ranges are similar to adults but vary in the earliest years of life. Newborns normally run between 30 and 60 mg/dL, which would be alarmingly low for an adult but is appropriate for their size and metabolism. By infancy, the range widens to 40 to 90 mg/dL, and by age two, children settle into the 60 to 100 mg/dL range that closely mirrors the adult standard.
When Blood Sugar Drops Too Low
Blood sugar below 70 mg/dL is classified as low (hypoglycemia). Below 54 mg/dL is considered severe. In people without diabetes, true hypoglycemia is uncommon but can happen after prolonged fasting, intense exercise on an empty stomach, or excessive alcohol intake.
Symptoms of low blood sugar include shakiness, sweating, confusion, irritability, and a fast heartbeat. These symptoms overlap with anxiety, which is one reason people sometimes confuse the two. If you eat something and the symptoms resolve within 15 minutes, low blood sugar was likely the cause.
Why Your Numbers Fluctuate
Even with perfectly healthy metabolism, your blood sugar doesn’t stay constant. Several everyday factors push it around.
Stress triggers a “fight or flight” hormone response that tells your liver to dump glucose into the bloodstream for quick energy. This can spike blood sugar noticeably, even if you haven’t eaten anything. Paradoxically, stress can also cause blood sugar crashes when the hormonal surge triggers a burst of insulin that overcorrects.
Poor sleep makes your body less responsive to insulin, leading to higher and more erratic blood sugar the following day. Even one night of short or interrupted sleep can have a measurable effect.
Exercise generally lowers blood sugar, but intense or prolonged workouts without fuel beforehand can cause it to drop too far. On the flip side, very high-intensity exercise (like sprinting or heavy lifting) can temporarily raise blood sugar because stress hormones kick in during the effort.
In the early morning hours, typically between 3 a.m. and 8 a.m., your body releases cortisol and growth hormone that naturally raise blood sugar to help you wake up. In people without diabetes, the pancreas compensates with enough insulin to keep levels in range. This is why fasting morning numbers can occasionally be slightly higher than you’d expect, even on a healthy day.