A normal fasting blood glucose level is below 100 mg/dL (5.6 mmol/L). That’s the number most people are looking for when they search this question, but blood sugar is measured in several different ways, each with its own “normal.” Here’s what each one means and how to read your results.
Fasting Blood Sugar Levels
A fasting blood sugar test measures your glucose after at least eight hours without food, typically first thing in the morning. The thresholds are straightforward:
- Normal: below 100 mg/dL
- Prediabetes: 100 to 125 mg/dL
- Diabetes: 126 mg/dL or higher on two separate tests
That two-test requirement matters. A single high reading can reflect stress, illness, a poor night of sleep, or even a medication side effect. A diabetes diagnosis requires confirmation, not just one elevated number.
After-Meal Blood Sugar
Your blood sugar naturally rises after eating, then drops back down as your body processes the glucose. In a healthy person, levels typically peak about one to two hours after a meal and return close to baseline within three hours. For people with diabetes who monitor after meals, the general target is to stay below 180 mg/dL at the two-hour mark, though individual goals vary.
If you don’t have diabetes and you’re checking out of curiosity with a home meter, a reading under 140 mg/dL two hours after eating is typical. What you ate matters a great deal. A bowl of white rice will spike your blood sugar faster and higher than a plate of grilled chicken and vegetables, even if both meals have the same calorie count. That spike isn’t necessarily dangerous in a healthy body, but consistently elevated post-meal numbers can be an early sign that your insulin response is starting to slow down.
How Your Body Regulates Blood Sugar
Your body works hard to keep blood sugar in a narrow band. Two hormones do most of the work: insulin brings blood sugar down, and glucagon brings it back up. Think of insulin as a key that unlocks cells throughout your body so glucose can move out of your bloodstream and into those cells, where it’s used for energy. When blood sugar drops too low (between meals, during sleep, or after exercise), your pancreas releases glucagon, which signals the liver to release stored glucose back into the blood.
This system runs constantly, adjusting in real time. Problems develop when the cells stop responding well to insulin (insulin resistance) or when the pancreas can’t produce enough of it. Both lead to glucose building up in the bloodstream instead of entering cells, which is what shows up as a high reading on a blood test.
A1C: The Three-Month Average
While a fasting test captures a single moment, the A1C test reflects your average blood sugar over roughly the past two to three months. It measures the percentage of your red blood cells that have glucose attached to them. The ranges, from the National Institute of Diabetes and Digestive and Kidney Diseases:
- Normal: below 5.7%
- Prediabetes: 5.7% to 6.4%
- Diabetes: 6.5% or above
A1C is useful because it isn’t affected by what you ate last night or whether you remembered to fast. It gives a broader picture. However, certain conditions that affect red blood cells, like iron deficiency anemia or sickle cell trait, can make A1C results less accurate. Your doctor may rely more heavily on fasting or post-meal tests in those cases.
Blood Sugar During Pregnancy
Pregnancy uses different, tighter thresholds. Gestational diabetes screening usually happens between weeks 24 and 28, and the cutoffs are lower than the standard diabetes numbers because even mildly elevated blood sugar during pregnancy can affect the baby.
The initial screening involves drinking a glucose solution and having blood drawn one hour later. A reading of 190 mg/dL or higher at that point indicates gestational diabetes. If the result falls between 140 and 189, a follow-up three-hour test is used, with these upper limits at each time point:
- Fasting: 95 mg/dL or lower
- One hour: 180 mg/dL or lower
- Two hours: 155 mg/dL or lower
- Three hours: 140 mg/dL or lower
Meeting or exceeding two or more of those thresholds leads to a gestational diabetes diagnosis. Some providers use a standalone two-hour test instead, which has slightly different cutoffs: a fasting level of 92 mg/dL or higher, 180 mg/dL or higher at one hour, or 153 mg/dL or higher at two hours.
Time in Range for CGM Users
Continuous glucose monitors (CGMs) track blood sugar around the clock, producing hundreds of readings per day. For people who use one, the key metric is “time in range,” which is the percentage of the day spent between 70 and 180 mg/dL. The American Diabetes Association recommends aiming for at least 70% of readings in that range, which works out to roughly 17 out of 24 hours.
CGMs reveal something that finger-prick tests can’t: how much your blood sugar fluctuates throughout the day. Two people can have the same A1C but very different daily patterns. One might hold steady between 90 and 140 most of the day, while the other swings from 60 to 250 and back. Time in range captures that difference in a way that averages alone miss.
Factors That Shift Your Numbers
Blood sugar isn’t static, and plenty of things beyond food can move it. Exercise typically lowers blood sugar by making your muscles take up glucose without needing as much insulin. Stress and illness raise it because your body releases hormones that push stored glucose into the bloodstream to fuel a “fight or flight” response. Poor sleep, even a single short night, can temporarily increase insulin resistance the next day.
Age and overall health also play a role. Targets for older adults or people managing multiple health conditions are sometimes adjusted to be slightly more lenient, because the risks of blood sugar dropping too low (dizziness, falls, confusion) can outweigh the risks of running a bit higher. Your targets may not match the standard numbers listed above, and that’s fine as long as the adjustment is intentional.
Medications outside of diabetes drugs can also affect readings. Steroids like prednisone are well known for raising blood sugar, sometimes dramatically. Some blood pressure medications, antipsychotics, and even high-dose niacin supplements can nudge numbers upward. If your results seem off after starting a new medication, that’s worth flagging.