What Is a Good Blood Sugar Level? Ranges by Age

A good fasting blood sugar level for most adults falls between roughly 70 and 100 mg/dL (3.9–5.6 mmol/L), while post-meal readings typically peak below 140 mg/dL (7.8 mmol/L) in people without diabetes. Those numbers, though, shift meaningfully depending on your age, whether you are pregnant, what medications you take, and how your body processes insulin. Understanding the full picture requires looking at more than a single morning reading.

Standard Ranges for Healthy Adults

If you have not been diagnosed with diabetes or prediabetes, the widely accepted benchmarks go like this: a fasting blood sugar (measured after at least eight hours without food) between about 70 and 99 mg/dL is considered normal. After eating, your blood sugar rises, and in a healthy person it generally returns below 140 mg/dL within about two hours. Your body manages this through a tightly coordinated system in which the pancreas releases insulin to bring glucose down and glucagon to push it back up when it drops too low, with additional signaling from the brain, liver, gut, and muscle tissue all playing a role.¹ Glucagon, specifically, works by triggering the liver to release stored glucose and produce new glucose when blood sugar falls.²

These ranges are population-level guidelines. In practice, healthy individuals show some natural variability. One continuous glucose monitoring study found that people without diabetes spent about 96% of their time within a glucose range of 3.9 to 7.8 mmol/L (roughly 70–140 mg/dL), which means brief spikes above that window are not unusual even in healthy people.³ A spike after a carb-heavy meal that briefly touches 150 mg/dL is not automatically a sign of trouble if your levels return to baseline quickly.

Newborns and Children

The first hours of life are an exception to nearly every glucose rule. In a healthy full-term newborn, blood sugar can drop as low as about 1.4 mmol/L (roughly 25 mg/dL) and climb as high as 6.2 mmol/L (about 112 mg/dL) during the immediate post-birth period. By around 72 hours of age, fasting glucose settles into the same range seen in older children and adults: about 3.5–5.5 mmol/L (63–99 mg/dL).⁴ That wide early swing is a normal part of the transition from receiving a steady glucose supply through the placenta to regulating blood sugar independently.

For children and adolescents without diabetes, the reference range is essentially the same as for adults once those first few days are past. Kids do tend to have slightly more brisk insulin responses, so post-meal spikes may resolve faster. The clinical concern in pediatrics is usually about blood sugar dropping too low (especially in ill or premature infants) rather than running too high.

How Aging Shifts Glucose Control

As you get older, your body becomes progressively less efficient at handling glucose. Research in older men has documented that glucose tolerance drops with age and that the decline comes from two simultaneous problems: beta cells in the pancreas do not secrete insulin as effectively, and the body’s tissues become more resistant to the insulin that is produced.⁵ One study found insulin sensitivity in older men was reduced by about 63% compared to younger men, even after accounting for differences in body fat.⁵

Additional research confirms that under conditions of high glucose challenge, older people produce less insulin than younger people and may also have a reduced sensitivity to incretin hormones, which are gut signals that stimulate insulin release after you eat.⁶ Insulin resistance itself tends to increase with age, with the body’s cellular protective responses to insulin-related stress becoming weaker over time.⁷

This means that a fasting blood sugar of, say, 105 mg/dL in a 75-year-old is far more common than in a 25-year-old, and clinicians sometimes accept slightly higher targets in older adults to avoid the risks of overtreatment, particularly dangerous low blood sugar episodes. For older adults with diabetes, guidelines generally allow more relaxed targets, recognizing that aggressive glucose lowering in someone with multiple health conditions can cause more harm than a modestly elevated reading.

Blood Sugar Targets During Pregnancy

Pregnancy changes glucose regulation. Hormones produced by the placenta naturally increase insulin resistance as the pregnancy progresses, which means blood sugar after meals tends to creep higher in the second and third trimesters. Continuous glucose monitoring in healthy pregnant women has shown that average post-meal glucose rises from about 95 mg/dL around 16 weeks to roughly 111 mg/dL by 36 weeks, then drops back after delivery.⁸

For women diagnosed with gestational diabetes, the treatment targets are tighter than those for the general population. The commonly used threshold for one-hour post-meal glucose is under 140 mg/dL, but research comparing that cutoff with a stricter target of under 120 mg/dL found that the lower target led to fewer oversized babies and fewer large-for-gestational-age deliveries, without increasing the rate of undersized babies.⁹ The higher threshold was itself an independent predictor of both macrosomia and large-for-gestational-age births. In practice, many clinicians now lean toward the lower target. When using continuous glucose monitors during pregnancy, the recommended time-in-range window narrows to 3.5–7.8 mmol/L (about 63–140 mg/dL), tighter than the 3.9–10.0 mmol/L range used for adults with diabetes outside of pregnancy.¹⁰

Where Prediabetes and Diabetes Begin

Prediabetes sits in a middle zone: blood sugar levels above normal but not yet high enough to qualify as diabetes.¹¹ The standard cutoffs are:

• Fasting glucose: 100–125 mg/dL is prediabetes; 126 mg/dL or higher on two separate tests indicates diabetes.
• Two-hour oral glucose tolerance test: 140–199 mg/dL is prediabetes; 200 mg/dL or higher indicates diabetes.
• HbA1c: 5.7–6.4% is prediabetes; 6.5% or higher indicates diabetes.

An important wrinkle is that the two main forms of prediabetes, impaired fasting glucose and impaired glucose tolerance, are not identical. They share the same core problems of insulin resistance and beta-cell dysfunction, but the location and pattern of these problems differ. Impaired glucose tolerance (where the two-hour post-challenge number is elevated) carries a stronger association with cardiovascular risk than impaired fasting glucose alone.¹² Someone with a normal fasting number but a high two-hour reading is not in the clear. If your doctor only checks fasting glucose, that form of prediabetes can go undetected.

What Moves Blood Sugar Throughout the Day

Your blood sugar is not static. Multiple factors push it up and down from hour to hour, and understanding these helps you interpret any reading you get.

Food composition matters more than most people realize. Eating carbohydrates alone produces a sharper glucose spike than eating those same carbohydrates alongside protein. In one trial, adding protein to a carbohydrate load significantly blunted the 60-minute glucose peak compared to carbohydrates eaten by themselves.¹³ Another study found that combining all three macronutrients (carbohydrate, protein, and fat together) produced a significantly lower glucose response than eating carbs paired with just one other macronutrient.¹⁴ The practical takeaway: a bowl of plain white rice will spike your sugar more than the same rice served with vegetables, eggs, and some fat.

Exercise is one of the most powerful tools for lowering blood sugar. A single bout of physical activity increases glucose uptake by your muscles, and regular training improves mitochondrial function and boosts the number of glucose transporter proteins your muscles produce.¹⁵ Even a 15-minute walk after a meal can noticeably flatten the post-meal glucose curve.

Sleep deprivation pushes blood sugar in the wrong direction. Studies in young healthy volunteers have shown that chronic short sleep raises evening cortisol, increases insulin levels, and elevates blood glucose.¹⁶ Sleep loss has also been linked to impaired glucose metabolism alongside increased inflammatory markers.¹⁷ A few nights of poor sleep can make your glucose readings look worse than your long-term metabolic health actually warrants, so a single elevated morning number after a terrible night of sleep is not necessarily cause for alarm.

The Morning Spike

Many people notice that their fasting blood sugar first thing in the morning is higher than readings taken later in the day, sometimes even higher than their pre-bedtime number. This is often the dawn phenomenon: in the early morning hours, the body releases surges of counter-regulatory hormones (growth hormone, cortisol, catecholamines) that reduce insulin’s effectiveness. In people without diabetes, the pancreas simply ramps up insulin to compensate. In people with diabetes, that compensatory mechanism is weakened, so blood sugar climbs.¹⁸

A separate phenomenon, the Somogyi effect, can look similar but has the opposite cause: it happens when too much insulin (from medication) drops blood sugar too low overnight, triggering a rebound rise. Distinguishing between the two matters because the fixes are opposite: the dawn phenomenon may call for adjusting the timing of medication, while the Somogyi effect calls for reducing nighttime insulin doses.

How the Menstrual Cycle Affects Glucose

If you menstruate, your blood sugar fluctuates with your cycle in ways that are measurable but often go unmentioned. Continuous glucose monitoring data show that glucose levels tend to be lowest during the late follicular phase (around day 13 or 14 of the cycle) and highest during the luteal phase (around day 24 or 25). The difference is modest, roughly 0.3 mmol/L (about 5 mg/dL) on average, but it is statistically significant and consistent. Higher estrogen levels are associated with lower glucose, while the hormonal shifts around ovulation and into the luteal phase push glucose slightly upward.¹⁹

Research into the mechanism suggests that glucose tolerance is greatest during the follicular phase, though more studies are needed to confirm this pattern fully.²⁰ The practical implication: if you are tracking glucose and notice slightly higher readings in the week or two before your period, the cycle itself may be the explanation rather than a change in diet or activity.

When HbA1c Can Mislead

HbA1c is the go-to lab test for assessing average blood sugar over the previous two to three months, and its thresholds (below 5.7% for normal, 5.7–6.4% for prediabetes, 6.5% and above for diabetes) are used globally. But HbA1c is not foolproof. The test measures how much glucose has attached to your hemoglobin, which means anything that changes your red blood cells can throw off the result. Iron-deficiency anemia, hemoglobin variants (common in people of African, Mediterranean, and Southeast Asian descent), recent blood transfusions, chronic kidney disease, and certain medications can all produce falsely high or falsely low readings.²¹

When HbA1c does not align with what day-to-day glucose readings suggest, or when someone belongs to a population where hemoglobin variants are prevalent, clinicians may turn to an oral glucose tolerance test for a more direct assessment.²² Non-glucose-related biological variation in HbA1c also adds uncertainty to the measurement, meaning that a difference of 0.2–0.3 percentage points between two tests may just be measurement noise rather than a real change in glucose control.²³

Continuous Glucose Monitoring and Time in Range

For people who use a continuous glucose monitor (CGM), the conversation around “good blood sugar” is shifting from individual snapshots to a metric called time in range, or TIR. TIR is defined as the percentage of the day your glucose stays within a target window, typically 3.9–10.0 mmol/L (about 70–180 mg/dL) for most adults with diabetes.²⁴ The consensus recommendation for most people with type 1 or type 2 diabetes is a TIR above 70%, with less than 4% of time spent below 3.9 mmol/L and less than 1% below 3.0 mmol/L. Older adults or people at high risk for low blood sugar get more relaxed targets.¹⁰

TIR adds context that a single fasting number cannot. Two people with the same average glucose might have wildly different TIR: one could be steady all day, while the other swings between high and low extremes that average out to the same number. The second person faces more risk. CGMs are increasingly used by people without diabetes, too, often for curiosity or optimization. For those users, TIR tends to be naturally very high, and occasional spikes that briefly leave the range are generally benign.

When Blood Sugar Drops Too Low

Most of the conversation around blood sugar focuses on levels being too high, but hypoglycemia (low blood sugar) can be more immediately dangerous. Symptoms of low blood sugar fall into two categories: autonomic symptoms like trembling, sweating, rapid heartbeat, and hunger, and neuroglycopenic symptoms like confusion, weakness, and in severe cases seizure or loss of consciousness.²⁵ The classical laboratory threshold for hypoglycemia is a plasma glucose of 50 mg/dL or below in combination with symptoms.²⁶

But the glucose level at which you actually feel those symptoms varies enormously based on your recent glucose history. In people with poorly controlled diabetes who have been running high for a while, symptoms of hypoglycemia can begin at glucose levels around 78 mg/dL, a level that would feel perfectly normal for someone without diabetes. By contrast, people without diabetes typically do not experience symptoms until glucose drops to roughly 53 mg/dL.²⁷ This is part of why someone newly starting insulin or glucose-lowering medication may feel shaky at blood sugar levels that are technically in the normal range: their body has adapted to running higher and interprets the drop as dangerous, even when it is not.

On the other end, repeated episodes of low blood sugar can shift the symptom threshold downward, creating a condition called hypoglycemia unawareness, where the warning signs (trembling, sweating) stop appearing until glucose falls to dangerously low levels.²⁵ This is one of the most serious complications of tight glucose management in people with type 1 diabetes.

Ethnic and Racial Differences in Glucose Handling

Blood sugar ranges and the tests used to measure them do not behave identically across all populations. Insulin sensitivity, insulin secretion in response to food, and the glycemic response to carbohydrates all differ by ethnicity.²⁸ A systematic review and meta-analysis found that when you map the relationship between insulin sensitivity and insulin secretion across populations, Caucasian subgroups tended to cluster near the middle of the curve, while African and East Asian subgroups were positioned at more extreme points, where a small shift in one variable triggers a disproportionately large swing in the other.²⁹

This has real clinical implications. HbA1c readings may not map to average glucose in the same way across racial groups, partly due to differences in red blood cell lifespan and glycation rates. Two people with the same daily glucose average can have meaningfully different HbA1c values simply because of genetic variation in hemoglobin behavior. If you are in a population where this discordance is more common, a direct glucose measurement or an oral glucose tolerance test may give you a more accurate picture of your metabolic health than relying on HbA1c alone.