A good fasting blood sugar reading falls between 70 and 99 mg/dL. That range applies to anyone without diabetes who hasn’t eaten for at least eight hours. Once you cross 100 mg/dL fasting, you’re in prediabetes territory, and 126 mg/dL or higher on two separate tests points to diabetes. But fasting numbers are only part of the picture. What counts as “good” shifts depending on when you last ate, whether you’re pregnant, and whether you’re already managing diabetes.
Fasting Blood Sugar Ranges
Fasting blood sugar is measured after you’ve gone at least eight hours without eating, typically first thing in the morning. The three categories break down clearly:
- Normal: 70 to 99 mg/dL (3.9 to 5.5 mmol/L)
- Prediabetes: 100 to 125 mg/dL (5.6 to 6.9 mmol/L)
- Diabetes: 126 mg/dL or higher on two separate tests
If you’re using a home glucose meter and consistently seeing numbers in the low 100s, that doesn’t mean you have diabetes, but it does mean your body is starting to have trouble processing sugar efficiently. Prediabetes is reversible for many people through changes in diet, activity, and weight.
After-Meal Readings
Blood sugar naturally rises after you eat. A spike to 140 or 150 mg/dL after a carb-heavy meal is completely normal for someone without diabetes. The key number to watch is where you land about two hours after the start of a meal. For most people, that reading should be below 140 mg/dL. A result above 200 mg/dL at the two-hour mark on a formal glucose tolerance test indicates diabetes, while 140 to 199 mg/dL falls in the prediabetes range.
If you have diabetes and are checking your own blood sugar, the general target is below 180 mg/dL two hours after eating. Your personal target may be tighter or more relaxed depending on your treatment plan, age, and other health conditions.
The A1C Test: Your Long-Term Average
A single finger-stick reading is a snapshot. The A1C test gives you the bigger picture by measuring your average blood sugar over the previous two to three months. It’s reported as a percentage rather than mg/dL.
- Normal: below 5.7%
- Prediabetes: 5.7% to 6.4%
- Diabetes: 6.5% or higher
A1C is useful because it isn’t thrown off by a single bad day of eating or a stressful morning. It reflects how your blood sugar has been behaving over weeks, which makes it a better predictor of complications than any individual reading. Most people with diabetes aim to keep their A1C below 7%, though the right target varies from person to person.
When Blood Sugar Drops Too Low
Low blood sugar, or hypoglycemia, is defined as anything below 70 mg/dL. It’s most common in people taking insulin or certain diabetes medications, but it can also happen after intense exercise, skipping meals, or drinking alcohol on an empty stomach. Symptoms include shakiness, sweating, confusion, irritability, and a racing heartbeat.
Below 54 mg/dL is considered severe hypoglycemia. At that level, you may need someone else’s help to recover because your thinking and coordination are impaired. If you monitor your blood sugar regularly and see readings in the low 60s, eating a fast-acting source of sugar (juice, glucose tablets, regular soda) and rechecking in 15 minutes is the standard approach.
When Blood Sugar Stays Too High
Readings above 180 mg/dL are considered high blood sugar. An occasional post-meal spike above that line isn’t uncommon for someone with diabetes, but staying there for hours or seeing fasting numbers in that range signals that something needs to change. Persistent high blood sugar causes increased thirst, frequent urination, blurry vision, and fatigue. Over months and years, it damages blood vessels, nerves, kidneys, and eyes.
Numbers above 250 mg/dL, especially with symptoms like nausea or fruity-smelling breath, can indicate a dangerous condition called diabetic ketoacidosis in people with type 1 diabetes. If you see readings consistently above 250, contact your care team promptly.
Blood Sugar Targets During Pregnancy
Pregnant women are held to tighter blood sugar standards because elevated glucose can affect the baby’s growth and increase delivery complications. The American College of Obstetricians and Gynecologists recommends these targets:
- Fasting: below 95 mg/dL
- One hour after eating: below 140 mg/dL
- Two hours after eating: below 120 mg/dL
These apply to women with gestational diabetes as well as those who had type 1 or type 2 diabetes before pregnancy. Most women with gestational diabetes check their blood sugar four or more times a day: once fasting and after each main meal.
Blood Sugar in Children
Normal fasting blood sugar for children over age two is roughly the same as for adults: 60 to 100 mg/dL. Younger children and infants run slightly lower, with normal ranges for newborns starting as low as 30 mg/dL and infants typically falling between 40 and 90 mg/dL. These lower ranges reflect the smaller glycogen stores that babies have, not a health problem.
For children with type 1 diabetes, target ranges are individualized, but the general goal is to keep blood sugar within a window that avoids both the symptoms of highs and the danger of lows, which children are less able to recognize and articulate on their own.
mg/dL vs. mmol/L
If you’re reading health information from the UK, Canada, Australia, or most of Europe, you’ll see blood sugar reported in mmol/L instead of mg/dL. The conversion is straightforward: divide mg/dL by 18 to get mmol/L. So a fasting reading of 99 mg/dL equals about 5.5 mmol/L, and the diabetes threshold of 126 mg/dL equals 7.0 mmol/L. If your meter reads in mmol/L, a good fasting number is between 3.9 and 5.5.
What Affects Your Reading
Blood sugar doesn’t sit at one number all day. It fluctuates in response to food, physical activity, stress, sleep quality, illness, and medications. A reading of 105 mg/dL after a night of poor sleep doesn’t carry the same weight as 105 mg/dL on a well-rested morning with consistent habits. Trends matter more than any single number.
Caffeine can raise blood sugar modestly in some people. So can the “dawn phenomenon,” a natural surge of hormones in the early morning that pushes fasting glucose higher than it would be at, say, 2 a.m. Dehydration concentrates your blood and can make readings appear slightly elevated. If a reading surprises you, washing your hands and retesting is a reasonable first step, since residue on your fingers (from fruit, lotion, or sugar) can skew the result.
The most useful thing you can do with blood sugar data is look for patterns over days and weeks rather than reacting to every individual number. A journal or app that tracks your readings alongside what you ate, how you slept, and how active you were will reveal far more than any single test.