A good fasting blood glucose level is below 100 mg/dL, and a healthy reading two hours after eating stays below 140 mg/dL. These numbers apply to adults without diabetes and serve as the baseline for understanding where your blood sugar stands. But “good” depends on context: whether you’re fasting or just ate, whether you’re pregnant, whether you manage diabetes, and even your age.
Fasting Blood Glucose: The Baseline Number
Fasting blood glucose is measured after at least eight hours without food, typically first thing in the morning. The American Diabetes Association breaks fasting levels into three categories:
- Normal: below 100 mg/dL (5.6 mmol/L)
- Prediabetes: 100 to 125 mg/dL
- Diabetes: 126 mg/dL or higher
If your fasting glucose lands between 100 and 125, your body is starting to have trouble processing sugar efficiently, but the condition is often reversible with changes to diet, exercise, and weight. A single reading at 126 or above doesn’t seal a diagnosis on its own. The test is typically repeated on a separate day to confirm.
After-Meal Glucose Levels
Your blood sugar naturally rises after eating, then comes back down as insulin moves glucose into your cells. In people without diabetes, that post-meal peak generally stays below 140 mg/dL when measured two hours after eating. A reading between 140 and 199 mg/dL at the two-hour mark falls into prediabetes territory, and 200 mg/dL or above points to diabetes.
The size and speed of that spike depend largely on what you ate. A meal heavy in refined carbohydrates (white bread, sugary drinks, white rice) sends glucose up faster and higher than a meal built around protein, fat, and fiber. This is why two people with identical fasting numbers can have very different post-meal patterns.
A1C: Your Two-to-Three-Month Average
While fasting and post-meal readings capture a single moment, the A1C test reflects your average blood sugar over roughly two to three months. It measures the percentage of hemoglobin in your red blood cells that has glucose attached to it. The higher your blood sugar has been running, the higher the percentage.
- Normal: below 5.7%
- Prediabetes: 5.7% to 6.4%
- Diabetes: 6.5% or higher
Each A1C percentage corresponds to an estimated average glucose. An A1C of 6% translates to an average of about 126 mg/dL. At 7%, the average is roughly 154 mg/dL. By 9%, you’re looking at an average around 212 mg/dL. For people already managing diabetes, most guidelines aim for an A1C below 7%, though individual targets vary.
When Blood Sugar Drops Too Low
Low blood sugar, or hypoglycemia, is primarily a concern for people taking insulin or certain diabetes medications, but it’s worth understanding the thresholds. A reading below 70 mg/dL is considered mild hypoglycemia and may cause shakiness, sweating, or irritability. Below 54 mg/dL is clinically significant and can lead to confusion, blurred vision, or difficulty concentrating. Severe hypoglycemia involves altered mental or physical functioning serious enough that you need someone else’s help to recover, regardless of the specific number on the meter.
For most people not on diabetes medication, the body’s own hormones prevent glucose from dropping dangerously low. But skipping meals, intense exercise, or heavy alcohol consumption can occasionally push levels below 70 in otherwise healthy individuals.
Glucose Targets During Pregnancy
Pregnancy tightens the window for healthy blood sugar because elevated glucose crosses the placenta and affects the baby’s growth. The American College of Obstetricians and Gynecologists recommends these targets for pregnant women managing diabetes:
- Fasting: below 95 mg/dL
- One hour after eating: below 140 mg/dL
- Two hours after eating: below 120 mg/dL
These numbers are lower than the general population thresholds because even moderately elevated glucose during pregnancy raises the risk of complications like high birth weight, preterm delivery, and preeclampsia. Women diagnosed with gestational diabetes typically monitor their blood sugar four or more times daily to stay within these tighter ranges.
Adjusted Targets for Older Adults
For older adults with diabetes, especially those with other chronic conditions, glucose targets are often relaxed rather than tightened. The reasoning is straightforward: aggressive treatment to push A1C below 6% with complex medication regimens significantly increases the risk of dangerous low blood sugar episodes. For someone in their 70s or 80s, a severe hypoglycemic event (a fall, loss of consciousness, confusion) can be more immediately harmful than running slightly above the standard target.
Treatment plans for older adults prioritize medications with a low risk of hypoglycemia and focus on avoiding both extreme highs and lows rather than chasing a perfect number.
Continuous Glucose Monitors and Time in Range
If you use a continuous glucose monitor (CGM), you’ll encounter a metric called “time in range,” which tracks the percentage of the day your glucose stays between 70 and 180 mg/dL. This range is wider than the fasting target because it accounts for natural post-meal rises throughout the day.
For most adults with type 1 or type 2 diabetes, the goal is spending more than 70% of the day (roughly 17 hours) in that 70 to 180 window. For older or higher-risk individuals, the target drops to more than 50% (about 12 hours). During pregnancy with type 1 diabetes, the target range narrows to 63 to 140 mg/dL, again reflecting the need for tighter control.
What makes time in range useful is that it captures the full picture of daily glucose behavior, not just a snapshot. Every 5% improvement in time in range is associated with meaningful health benefits, which means even incremental progress matters. A person who moves from 55% to 65% in range is making a clinically significant difference even without hitting the 70% target.
What Affects Your Numbers Day to Day
Blood sugar isn’t static, even in perfectly healthy people. A number of everyday factors push it up or down. Stress hormones raise glucose, which is why a bad night’s sleep or a high-pressure morning can show up on your meter. Physical activity pulls glucose into muscles for energy, often lowering readings for hours afterward. Illness and infection trigger the body’s stress response and can spike glucose even if you haven’t changed what you eat. Dehydration concentrates glucose in the blood, making readings appear higher.
Caffeine affects some people more than others, with studies showing it can temporarily reduce insulin sensitivity. Even the order you eat your food matters: starting a meal with vegetables or protein before carbohydrates tends to blunt the post-meal spike compared to eating carbs first. These variables explain why you can eat the same breakfast two days in a row and get different readings each time. The overall pattern matters far more than any single number.