A healthy fasting blood sugar is below 100 mg/dL (5.6 mmol/L). After eating, blood sugar naturally rises but should return to the 70 to 140 mg/dL range within about two hours. These numbers apply to adults who are not pregnant, and they represent the range where your body is processing glucose efficiently without strain on the system.
Fasting Blood Sugar Ranges
Fasting blood sugar is measured after at least eight hours without eating, typically first thing in the morning. The ranges break down into three categories:
- Normal: below 100 mg/dL
- Prediabetes: 100 to 125 mg/dL
- Diabetes: 126 mg/dL or higher
It’s worth noting that the World Health Organization draws the prediabetes line slightly higher, at 110 mg/dL, while the American Diabetes Association lowered it to 100 mg/dL in 2003 to catch more people at risk. If your fasting number falls between 100 and 110, you’re in a gray zone where one set of guidelines flags you and another doesn’t. Either way, that range signals your body is starting to struggle with glucose regulation and warrants attention.
After-Meal Blood Sugar
Blood sugar always rises after you eat. That’s normal. In a healthy body, it peaks somewhere around 30 to 60 minutes after a meal, then drops back down. By the two-hour mark, a normal reading falls between 70 and 140 mg/dL. A reading of 140 to 199 mg/dL two hours after a standardized glucose test falls into the prediabetes range, and 200 mg/dL or above indicates diabetes.
Even in people with completely normal blood sugar regulation, glucose doesn’t stay perfectly flat throughout the day. A large study using continuous glucose monitors on people without diabetes found that their average glucose was about 114 mg/dL, and they spent roughly 87% of their time in the 70 to 140 mg/dL range. They still spent about three hours per day above 140 mg/dL, and some participants saw spikes as high as 376 mg/dL at their peak moments. So occasional post-meal spikes above 140 don’t automatically signal a problem.
A1C: The Bigger Picture
While fasting and post-meal readings capture a single moment, your A1C reflects your average blood sugar over the previous two to three months. It’s reported as a percentage:
- Normal: below 5.7%
- Prediabetes: 5.7% to 6.4%
- Diabetes: 6.5% or higher
A1C works by measuring how much glucose has attached to your red blood cells over their lifespan. It’s useful because it smooths out the daily ups and downs and shows whether your blood sugar is well-controlled on average, not just on the morning you happened to get tested.
How Your Body Keeps Blood Sugar Stable
Your pancreas produces two key hormones that work in opposition to keep glucose in a tight range. When you eat and blood sugar rises, your pancreas releases insulin, which signals your muscles, fat, and liver to absorb glucose from the bloodstream and store it for later. At the same time, glucagon (the opposing hormone) drops, telling your liver it doesn’t need to produce any extra glucose right now.
Between meals and overnight, the reverse happens. Insulin falls, glucagon rises, and your liver begins converting its stored glycogen back into glucose to keep your brain and body fueled. If those glycogen stores run low, the liver can also build new glucose from amino acids and fat byproducts. This is why you can go eight or ten hours overnight without eating and still wake up with blood sugar in a normal range.
Your gut also plays a role. When food arrives in your intestines, your gut releases signaling hormones that tell the pancreas to ramp up insulin production and dial down glucagon. This coordination is why blood sugar in a healthy person rises only modestly after meals and comes back down quickly.
Why Morning Blood Sugar Can Run High
Some people notice their fasting blood sugar is higher than expected, even when they ate well the night before. This is often due to the dawn phenomenon: in the early morning hours, roughly between 3 and 8 a.m., your body releases cortisol and growth hormone that tell the liver to push out more glucose. This provides the energy burst that helps you wake up. In a healthy person, the pancreas compensates with extra insulin. In someone with insulin resistance or diabetes, that compensation falls short, and morning readings creep up.
A related pattern called the Somogyi effect works differently. If blood sugar drops too low during the night (from skipping dinner or other causes), the body overcorrects by dumping glucose into the bloodstream, resulting in a high reading by morning. A large or late dinner can also keep blood sugar elevated overnight simply because the body is still processing the meal.
Targets During Pregnancy
Pregnancy tightens the acceptable ranges. The American College of Obstetricians and Gynecologists recommends that pregnant women aim for a fasting blood sugar below 95 mg/dL, below 140 mg/dL one hour after eating, and below 120 mg/dL two hours after eating. A1C should stay below 6%. These stricter targets exist because elevated blood sugar during pregnancy increases risks for both the mother and baby, including larger birth weight, preterm delivery, and complications during labor.
When Blood Sugar Drops Too Low
The floor matters too. For people without diabetes, blood sugar below 55 mg/dL is considered hypoglycemia. Symptoms include shakiness, sweating, confusion, irritability, and feeling lightheaded. In the continuous glucose monitor study of healthy individuals, participants spent less than 1% of their time below 70 mg/dL and almost no time below 54 mg/dL, so significant drops are uncommon in people with normal glucose regulation.
Low blood sugar in non-diabetic individuals can happen after prolonged fasting, intense exercise, or excessive alcohol consumption. Reactive hypoglycemia, where blood sugar dips a few hours after eating a high-carbohydrate meal, is another pattern some people experience. If you’re regularly feeling shaky or lightheaded between meals, that’s worth investigating rather than assuming it’s normal.
What Continuous Glucose Monitors Reveal
Continuous glucose monitors have given researchers a much more detailed picture of what “healthy” blood sugar actually looks like minute to minute. In a large community study of 560 people without diabetes, participants spent about 98% of their time between 70 and 180 mg/dL. Their median glucose was around 112 mg/dL, and even the healthiest participants saw their glucose fluctuate across a wide range throughout the day.
These findings are reassuring if you wear a CGM and notice your blood sugar isn’t a flat line. Healthy blood sugar is not static. It rises after meals, dips during exercise, and shifts overnight. The key indicator of metabolic health isn’t whether your glucose ever goes above 140, but how quickly it comes back down and how much of your day is spent in a reasonable range.