A normal fasting blood sugar level is below 100 mg/dL (5.6 mmol/L). That’s the number most people are looking for, but “normal” shifts throughout the day depending on when and what you’ve eaten, how active you are, and whether you’re pregnant. Here’s a full breakdown of what the numbers mean at every point.
Normal Fasting Blood Sugar
Fasting blood sugar is measured after you haven’t eaten for at least eight hours, usually first thing in the morning. For adults, the ranges break down like this:
- Normal: below 100 mg/dL (5.6 mmol/L)
- Prediabetes: 100 to 125 mg/dL (5.6 to 6.9 mmol/L)
- Diabetes: 126 mg/dL (7.0 mmol/L) or higher on two separate tests
Most healthy adults fall between 74 and 106 mg/dL when fasting. If your number lands in the prediabetes range, it doesn’t mean you’ll develop diabetes, but it does signal that your body is having a harder time processing sugar efficiently.
Blood Sugar After Eating
Your blood sugar naturally rises after a meal, peaks somewhere around 30 to 60 minutes in, and then comes back down. For someone without diabetes, the two-hour mark is the standard checkpoint: blood sugar should be below 140 mg/dL (7.8 mmol/L) by then. A result between 140 and 199 mg/dL at the two-hour mark falls into the prediabetes range, and 200 mg/dL or above points toward diabetes.
Continuous glucose monitors give us a clearer picture of what happens throughout the day. In a multicenter study of healthy, non-diabetic adults, participants spent 96% of their time with glucose between 70 and 140 mg/dL. Their blood sugar went above 140 mg/dL for only about 30 minutes per day on average. So brief spikes after eating are completely normal, as long as they come back down quickly.
A1C: Your Three-Month Average
While a finger-stick or fasting test captures one moment in time, 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.
- Normal: below 5.7%
- Prediabetes: 5.7% to 6.4%
- Diabetes: 6.5% or higher
A1C is useful because it isn’t thrown off by what you ate yesterday or how well you slept. It’s often the first test ordered if a doctor suspects blood sugar problems, and it’s the number used to track long-term management for people already diagnosed with diabetes.
When Blood Sugar Drops Too Low
Low blood sugar, or hypoglycemia, is generally defined as anything below 70 mg/dL (3.9 mmol/L). But most people don’t actually feel symptoms until their levels drop below 55 mg/dL. At that point, you might notice shakiness, sweating, a racing heart, confusion, or irritability. The threshold varies from person to person, which is why some people feel “off” at levels that wouldn’t bother someone else.
Hypoglycemia is most common in people taking insulin or certain diabetes medications, but it can also happen after prolonged fasting, intense exercise, or heavy alcohol use in people without diabetes.
How Exercise and Stress Shift Your Numbers
Intense exercise causes a small, temporary blood sugar rise even in healthy people. In one study, participants without diabetes saw their blood sugar go from about 90 mg/dL before a high-intensity workout to around 100 mg/dL about 10 minutes after finishing. That bump can persist for up to an hour before settling back to normal. It happens because your liver releases stored sugar to fuel your muscles during hard effort.
Stress triggers a similar response. When your body perceives a threat, whether physical or emotional, it dumps stress hormones into your bloodstream that tell the liver to release glucose. This is why a stressful day at work or a bad night of sleep can push fasting numbers higher than expected, even if your diet hasn’t changed.
Different Ranges for Children
Children’s normal blood sugar ranges are slightly different from adults, especially in the early years. Newborns have notably lower normal ranges (30 to 60 mg/dL), which gradually rise as they grow. By age two, the normal fasting range looks similar to an adult’s at 60 to 100 mg/dL. Infants and toddlers run lower than adults partly because their smaller bodies metabolize glucose differently, so a number that would concern you in an adult may be perfectly fine in a baby.
Blood Sugar Targets During Pregnancy
Pregnancy changes how your body handles sugar, and the screening thresholds are tighter than standard adult ranges. Most pregnant people take a one-hour glucose screening test between weeks 24 and 28. A result below 140 mg/dL is normal. If that number comes back high, the follow-up is a three-hour glucose tolerance test with stricter cutoffs:
- Fasting: below 95 mg/dL
- One hour: below 180 mg/dL
- Two hours: below 155 mg/dL
- Three hours: below 140 mg/dL
Gestational diabetes is diagnosed when two or more of those values come back above the threshold. It typically resolves after delivery, but it does increase the risk of developing type 2 diabetes later in life.
Converting Between mg/dL and mmol/L
If you’re reading results from a country that uses mmol/L (most of the world outside the U.S.), the conversion is straightforward: divide mg/dL by 18. So a fasting blood sugar of 100 mg/dL equals about 5.6 mmol/L. Going the other direction, multiply mmol/L by 18. Here are some common reference points:
- 70 mg/dL = 3.9 mmol/L (lower boundary of normal)
- 100 mg/dL = 5.6 mmol/L (upper limit of normal fasting)
- 126 mg/dL = 7.0 mmol/L (diabetes fasting threshold)
- 140 mg/dL = 7.8 mmol/L (normal post-meal cutoff)
- 200 mg/dL = 11.1 mmol/L (diabetes post-meal threshold)