A good fasting blood sugar level for most adults is below 100 mg/dL, and a reading under 140 mg/dL two hours after eating is considered normal. These two numbers give you the clearest snapshot of healthy blood sugar. But “good” shifts depending on your age, whether you’re pregnant, and whether you’re managing diabetes, so the full picture is worth understanding.
Normal Ranges at a Glance
Blood sugar is measured in milligrams per deciliter (mg/dL) in the U.S. The key benchmarks break into three categories: normal, prediabetes, and diabetes.
- Fasting blood sugar (no food for 8+ hours): Below 100 mg/dL is normal. Between 100 and 125 mg/dL falls into the prediabetes range. At 126 mg/dL or higher on two separate tests, it meets the threshold for diabetes.
- Two hours after eating: Below 140 mg/dL is normal. Between 140 and 199 mg/dL suggests prediabetes. At 200 mg/dL or above, it indicates diabetes.
- A1C (a 2–3 month average): Below 5.7% is normal. Between 5.7% and 6.4% is prediabetes. At 6.5% or higher, it’s diabetes.
A single high reading doesn’t mean much on its own. Diagnosis requires repeated testing or confirmation through a second method. What matters more than any one number is the pattern over time.
What A1C Tells You That a Single Reading Can’t
A fasting glucose test captures one moment. Your A1C captures the bigger picture by reflecting your average blood sugar over roughly three months. It works by measuring how much sugar has attached to your red blood cells, which turn over on that timeline. An A1C below 5.7% means your blood sugar has been consistently in a healthy range, even during the hours you weren’t testing.
This is why A1C is often the preferred screening tool. You don’t need to fast for it, and it isn’t thrown off by what you ate the night before. If your fasting glucose looks fine but your A1C is creeping above 5.7%, your blood sugar is likely spiking higher than normal after meals, even if it returns to baseline by morning.
After-Meal Spikes: What’s Normal
Blood sugar always rises after you eat. That’s expected. In a healthy metabolism, it peaks about 60 to 90 minutes after a meal and returns to near-fasting levels within two hours. A reading under 140 mg/dL at the two-hour mark is considered normal.
Most people without diabetes never notice these fluctuations because they stay well within range. But the size and duration of your post-meal spike is influenced by what you ate (refined carbs cause steeper rises than protein or fiber), how active you are after the meal, and how well your body produces and responds to insulin. Walking for even 10 to 15 minutes after eating can noticeably blunt a post-meal spike.
Targets During Pregnancy
Pregnancy tightens the window for what counts as a good sugar level. The American College of Obstetricians and Gynecologists recommends a fasting level below 95 mg/dL and a reading below 140 mg/dL one hour after eating for women with pre-existing diabetes. These targets are stricter than the general population’s because elevated blood sugar during pregnancy raises the risk of complications for both the mother and the baby, including higher birth weight and delivery difficulties.
Gestational diabetes, which develops during pregnancy in women who didn’t previously have diabetes, is typically screened for between weeks 24 and 28. If you’re diagnosed, you’ll track your blood sugar multiple times a day to stay within these tighter ranges.
How Targets Shift With Age
For younger adults with diabetes, tighter blood sugar control is generally the goal because they have decades ahead in which complications from elevated glucose (nerve damage, kidney problems, vision loss) could develop. For adults in their 80s or 90s, the calculus changes. The long-term risks of slightly elevated sugar become less relevant, while the immediate danger of blood sugar dropping too low becomes more serious.
Low blood sugar (hypoglycemia) can cause dizziness, confusion, falls, and loss of consciousness. Older adults are more vulnerable to these episodes, especially those with memory problems, physical frailty, vision issues, or serious heart, lung, or kidney conditions. For these individuals, the priority shifts from hitting a specific number to avoiding dangerous lows. An older adult in good overall health with few risk factors may still benefit from tighter targets, but this is always a personalized decision.
When Blood Sugar Drops Too Low
A blood sugar below 70 mg/dL is considered low, and it can cause noticeable symptoms: shakiness, sweating, irritability, and a feeling of sudden hunger. This level is classified as mild hypoglycemia and is usually easy to correct by eating 15 to 20 grams of fast-acting carbohydrates, like a few glucose tablets, half a cup of juice, or a tablespoon of honey.
Below 54 mg/dL is more serious. At this point, coordination and thinking can become impaired. Below that, or at any level where someone becomes confused, loses consciousness, or needs help from another person, it’s classified as severe hypoglycemia and is a medical emergency. People who don’t take insulin or blood sugar-lowering medications rarely experience levels this low.
When Blood Sugar Goes Too High
On the other end, symptoms of high blood sugar typically don’t appear until levels exceed 180 to 200 mg/dL. That means you can walk around with moderately elevated glucose for months or years without feeling anything obviously wrong, which is exactly why screening matters.
Once symptoms do appear, they tend to include increased thirst, frequent urination, blurred vision, and fatigue. Persistently elevated levels above 200 mg/dL, especially over weeks or months, accelerate damage to blood vessels, nerves, and organs. The absence of symptoms at slightly elevated levels is what makes prediabetes so easy to miss and so important to catch.
What Affects Your Numbers Day to Day
Blood sugar isn’t a fixed value. It fluctuates throughout the day based on food, activity, sleep, and stress. When you’re under acute stress, your body releases cortisol and adrenaline, which signal the liver to dump stored glucose into the bloodstream. At the same time, these hormones make your muscle and fat cells less responsive to insulin, so that extra glucose lingers longer. This is a survival mechanism, designed to fuel a quick physical response, but in modern life it mostly just raises your readings.
Poor sleep has a similar effect. Even one night of restricted sleep can temporarily reduce insulin sensitivity the next day. Illness and infection also raise blood sugar because the body’s inflammatory response triggers many of the same hormonal pathways as stress. If you’re testing at home and see an unexpectedly high reading, consider whether you’re sick, sleep-deprived, or under unusual stress before assuming the worst.
Continuous Glucose Monitors and Time in Range
If you use a continuous glucose monitor (CGM), the key metric to watch is “time in range,” which measures the percentage of the day your glucose stays between 70 and 180 mg/dL. For most people with type 1 or type 2 diabetes, the recommended target is spending more than 70% of the day in that range. That works out to roughly 17 hours out of 24.
Time in range is a more useful measure than any single reading because it captures the full picture: how high your spikes go, how quickly they come down, and how much time you spend at healthy levels overnight. A person with a great fasting glucose but large post-meal spikes throughout the day might have a lower time in range than their morning number would suggest.