A normal fasting blood sugar is below 100 mg/dL (5.6 mmol/L). That single number is the most common benchmark, but your sugar levels shift throughout the day, and the “right” range depends on when you last ate, whether you’re pregnant, and whether you’re managing diabetes or trying to prevent it. Here’s a full breakdown of the numbers that matter.
Normal Fasting Blood Sugar
Fasting blood sugar is measured after at least 8 hours without eating, typically first thing in the morning. For a healthy adult, the target is below 100 mg/dL. Most people without diabetes will land somewhere between 70 and 99 mg/dL.
If your fasting level falls between 100 and 125 mg/dL, that’s considered the prediabetes range. At 126 mg/dL or higher on two separate tests, the reading meets the diagnostic threshold for Type 2 diabetes.
Blood Sugar After Meals
Your blood sugar naturally rises after you eat. In someone without diabetes, it typically peaks about an hour after a meal and settles back down within two hours. A general guideline used during pregnancy (and widely referenced for healthy adults) sets the targets at below 140 mg/dL one hour after eating and below 120 mg/dL at two hours. Most healthy people stay well under these ceilings without thinking about it.
If you’re tracking your sugar after meals and consistently seeing readings above 140 at the one-hour mark, that pattern is worth investigating even if your fasting numbers look fine. Post-meal spikes can be an early sign that your body is struggling to manage glucose before fasting levels start creeping up.
What Your A1C Tells You
While a finger-stick reading captures a single moment, your A1C (also called HbA1c) reflects your average blood sugar over roughly the past 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
An A1C of 5.7% corresponds to an estimated average glucose of about 117 mg/dL. At 6.5%, that average climbs to roughly 140 mg/dL. If you’ve only ever checked fasting glucose, an A1C test gives a fuller picture because it captures how your body handles sugar around the clock, including after meals.
Blood Sugar Targets During Pregnancy
Pregnancy tightens the acceptable ranges. The American College of Obstetricians and Gynecologists recommends these goals for pregnant women with diabetes or gestational diabetes:
- Fasting: below 95 mg/dL
- One hour after eating: below 140 mg/dL
- Two hours after eating: below 120 mg/dL
The lower fasting target exists because elevated glucose during pregnancy affects both maternal and fetal health. Most pregnant women are screened for gestational diabetes between weeks 24 and 28 with a glucose tolerance test.
When Blood Sugar Is Too Low
The conversation around blood sugar usually focuses on highs, but lows matter too. Blood sugar below 70 mg/dL is considered low (hypoglycemia), and below 54 mg/dL is classified as severe. Symptoms of a low include shakiness, sweating, confusion, irritability, and a fast heartbeat. In severe cases, it can cause seizures or loss of consciousness.
Hypoglycemia is most common in people taking insulin or certain diabetes medications, but it can happen to anyone after prolonged fasting, intense exercise, or heavy alcohol consumption on an empty stomach. If you’re not on diabetes medication and regularly feel shaky or lightheaded between meals, those symptoms are worth mentioning to your doctor even if they seem minor.
Targets Shift With Age
Standard blood sugar thresholds were developed primarily from studies of younger and middle-aged adults. For people over 70, the picture looks different. Research from Johns Hopkins found that older adults with prediabetes-range blood sugar are actually more likely to see their levels return to normal over time than to progress to diabetes. The prediabetes label, in other words, is less predictive in this age group.
That doesn’t mean blood sugar is irrelevant for older adults, but it does mean that a fasting glucose of 105 in a 75-year-old carries different implications than the same number in a 40-year-old. For older adults, managing blood pressure, cholesterol, and other cardiovascular risk factors tends to have a bigger impact on health outcomes than chasing a fasting glucose number below 100.
If You Use a Continuous Glucose Monitor
Continuous glucose monitors (CGMs) track your sugar in real time and introduce a metric called “time in range.” The American Diabetes Association defines the target range as 70 to 180 mg/dL for most people. The goal is to spend at least 70% of your day, roughly 17 out of 24 hours, within that window.
CGMs reveal something that finger-stick tests can’t: how much your sugar fluctuates. You might have a perfect fasting number but spike to 160 after lunch every day. Or your overnight levels might dip into the low 60s without you knowing. If you wear a CGM, pay attention to the overall pattern and time in range rather than fixating on any single reading.
Surprising Things That Raise Blood Sugar
Food is the obvious driver, but plenty of non-food factors push your sugar up in ways you might not expect. Poor sleep is one of the most significant. Even a single night of inadequate rest reduces your body’s ability to use insulin effectively the next day. Skipping breakfast can also backfire, leading to higher sugar levels after both lunch and dinner compared to days when you eat a morning meal.
Stress raises blood sugar through hormones like cortisol and adrenaline, which is why pain (including something as simple as a sunburn) can cause a measurable spike. Caffeine affects some people more than others, but black coffee with no sweetener can still raise glucose in sensitive individuals. Dehydration concentrates the sugar already in your bloodstream, so staying well-hydrated helps keep readings stable. Even the time of day matters: blood sugar tends to be harder to control in the evening, and most people experience a natural hormone surge in the early morning hours (called the dawn phenomenon) that temporarily raises glucose before breakfast.
Understanding these factors helps explain why your readings might vary from day to day even when your diet stays consistent. A stressful week, a few nights of poor sleep, or a bout of dehydration can all shift your numbers independently of what you eat.