For most healthy adults, a normal fasting blood sugar is below 100 mg/dL (5.6 mmol/L), and a normal reading two hours after eating is below 140 mg/dL (7.8 mmol/L). Those thresholds apply broadly from young adulthood through old age, but children, pregnant women, and older adults with chronic conditions each have their own practical targets. Here’s how the numbers break down across life stages.
Normal Ranges for Adults
The American Diabetes Association uses three main tests to evaluate blood sugar, and each has its own scale. A fasting plasma glucose test measures your blood sugar after at least eight hours without food. A normal result is below 100 mg/dL. A reading between 100 and 125 mg/dL falls into the prediabetes range, and 126 mg/dL or higher indicates diabetes.
An oral glucose tolerance test checks how your body handles sugar by measuring blood glucose two hours after you drink a standardized sugary liquid. Below 140 mg/dL is normal, 140 to 199 mg/dL signals prediabetes, and 200 mg/dL or above points to diabetes.
The A1C test gives a broader picture. Instead of a single snapshot, it reflects your average blood sugar over the past two to three months, expressed as a percentage. Below 5.7% is normal, 5.7% to 6.4% is prediabetes, and 6.5% or higher typically means diabetes. These adult thresholds don’t shift based on whether you’re 25 or 55. The diagnostic cutoffs remain the same.
Blood Sugar Targets for Children
Children’s bodies are still developing, and blood sugar targets reflect that. Young children are especially vulnerable to dangerous lows, so their acceptable range is wider than what you’d see for an adult. The American Diabetes Association sets age-specific goals primarily for children who already have diabetes, but the ranges also help parents understand what’s typical.
For toddlers and preschoolers (ages 0 to 6), a target blood sugar range of 100 to 200 mg/dL is considered appropriate, with an A1C goal under 8.5% but above 7.5%. That wider window accounts for the fact that very young children can’t easily recognize or communicate symptoms of low blood sugar, and their eating patterns are unpredictable.
For school-age children (ages 6 to 12), the target tightens slightly to 90 to 180 mg/dL, with an A1C goal under 8%. By the teenage years, targets generally begin to align more closely with adult ranges, though individual circumstances vary. A healthy child without diabetes will typically have fasting glucose levels similar to healthy adults, well under 100 mg/dL.
How Pregnancy Changes the Numbers
During pregnancy, blood sugar standards become stricter because even mildly elevated glucose can affect fetal development. Screening for gestational diabetes usually happens between weeks 24 and 28. The initial screening is a glucose challenge test: you drink a sugary solution, and your blood is drawn one hour later. A result below 140 mg/dL is generally considered normal. A reading of 190 mg/dL or higher means gestational diabetes is diagnosed right away, while results in between prompt a longer follow-up test.
If you’re diagnosed with gestational diabetes, your care team will set tighter targets for daily monitoring. Fasting levels are typically expected to stay well below the standard 100 mg/dL cutoff, and post-meal readings are watched more closely than they would be outside of pregnancy. These stricter numbers usually apply only during the pregnancy itself, and glucose regulation often returns to normal after delivery.
Why Blood Sugar Regulation Shifts With Age
The diagnostic cutoffs for diabetes don’t change for older adults, but that doesn’t mean aging has no effect. As you get older, your cells gradually become less responsive to insulin, the hormone that moves sugar out of your bloodstream and into your cells. This is a well-documented part of aging. Insulin levels in the blood tend to rise over time as the body tries to compensate for that reduced sensitivity, but the compensation becomes less effective.
At a cellular level, several things contribute. Mitochondria, the structures inside cells that produce energy, become less efficient with age. They generate more waste products (free radicals) and less usable energy. The body’s ability to clear out damaged proteins and recycle cellular components also declines. Fat storage increases, and muscles, which are major consumers of blood glucose, tend to shrink. All of these shifts nudge fasting blood sugar and post-meal blood sugar gradually upward over the decades, even in people who remain healthy.
This means that a fasting glucose of 95 mg/dL in a 70-year-old, while technically normal, represents a different metabolic picture than the same reading in a 30-year-old. Some clinicians set slightly more relaxed blood sugar management targets for elderly patients with diabetes, particularly those with other serious health conditions, because the risks of aggressive blood sugar lowering (including dangerous lows) can outweigh the benefits in that population. But for diagnostic purposes, the cutoffs remain the same regardless of age.
When Screening Should Start
The U.S. Preventive Services Task Force recommends that adults aged 35 to 70 who are overweight or obese get screened for prediabetes and type 2 diabetes. If your initial results are normal, repeating the test every three years is a reasonable schedule. Earlier screening is recommended for people in populations with higher diabetes rates, including Black, Hispanic/Latino, American Indian/Alaska Native, and Native Hawaiian/Pacific Islander communities. Asian Americans are advised to screen at a lower weight threshold (a BMI of 23 or above, rather than the standard 25).
For children, routine screening isn’t standard unless risk factors are present, such as a strong family history of type 2 diabetes, obesity, or signs of insulin resistance like darkened skin patches on the neck or underarms.
mg/dL vs. mmol/L
If you live outside the United States, your blood sugar results are likely reported in mmol/L rather than mg/dL. The conversion is straightforward: divide mg/dL by 18 to get mmol/L. So a fasting level of 100 mg/dL equals about 5.5 mmol/L, and the diabetes threshold of 126 mg/dL converts to 7.0 mmol/L. The post-meal normal cutoff of 140 mg/dL is 7.8 mmol/L, and the diabetes diagnostic level of 200 mg/dL works out to 11.1 mmol/L.
Quick Reference by Age Group
- Toddlers and preschoolers (0 to 6): 100 to 200 mg/dL target range, A1C between 7.5% and 8.5%
- School-age children (6 to 12): 90 to 180 mg/dL target range, A1C under 8%
- Teens and adults: Fasting below 100 mg/dL, post-meal below 140 mg/dL, A1C below 5.7%
- Pregnant women: Stricter post-meal targets; screening result below 140 mg/dL is normal on the one-hour glucose challenge
- Older adults (65+): Same diagnostic cutoffs as younger adults, though individual management targets may be adjusted for those with multiple health conditions