A good fasting blood glucose reading is 99 mg/dL or below. That’s the benchmark for someone without diabetes, measured after at least eight hours without eating. But “good” depends on when you last ate, whether you have diabetes, and your age, so a single number only tells part of the story.
Fasting Blood Glucose Ranges
Fasting blood glucose is the most common test and the one most people picture when they think of a blood sugar reading. You take it first thing in the morning before eating or drinking anything other than water. The standard ranges break down into three categories:
- Normal: 99 mg/dL or below
- Prediabetes: 100 to 125 mg/dL
- Diabetes: 126 mg/dL or above
If you’re outside the U.S. and your meter reads in mmol/L, divide any mg/dL number by 18 to convert. A fasting reading of 99 mg/dL, for example, is about 5.5 mmol/L.
A single high reading doesn’t automatically mean you have diabetes. Stress, illness, poor sleep, and certain medications can all push your fasting number up temporarily. A diabetes diagnosis requires at least two separate high readings or a combination of abnormal results across different tests.
Blood Glucose After Eating
Your blood sugar naturally rises after a meal and peaks roughly 60 to 90 minutes later. For people with diabetes, the target is to stay below 180 mg/dL two hours after the start of a meal. In people without diabetes, blood sugar rarely exceeds 140 mg/dL after eating and typically returns to pre-meal levels within two to three hours.
If you’re checking your blood sugar at home, timing matters. Testing too soon after eating will almost always show a higher number, which can be misleading. The two-hour mark after your first bite is the standard window for a post-meal check.
A1C: The Bigger Picture
While a finger-stick reading captures a single moment, the A1C test reflects your average blood sugar over the previous two to three months. It measures the percentage of your red blood cells that have glucose attached to them. The ranges mirror the fasting test categories:
- Normal: below 5.7%
- Prediabetes: 5.7% to 6.4%
- Diabetes: 6.5% or above
For most adults already living with diabetes, the American Diabetes Association recommends keeping A1C below 7%. That roughly corresponds to an average blood sugar of about 154 mg/dL. This target balances good blood sugar control against the risk of dropping too low.
When Blood Sugar Drops Too Low
Most conversations focus on high blood sugar, but going too low is dangerous in the short term. The threshold for low blood sugar (hypoglycemia) is 70 mg/dL. Below that, you may feel shaky, sweaty, confused, or lightheaded. A reading below 54 mg/dL is considered clinically serious and requires immediate treatment with fast-acting sugar, like juice or glucose tablets.
Hypoglycemia is primarily a concern for people taking insulin or certain oral diabetes medications. If you don’t take these, your body’s hormonal systems will typically prevent your blood sugar from falling that low.
Time in Range for CGM Users
If you wear a continuous glucose monitor (CGM), you’ll see a metric called “time in range,” which tracks how many hours per day your blood sugar stays between 70 and 180 mg/dL. The goal for most adults with Type 1 or Type 2 diabetes is to spend at least 70% of the day in that range. For people who are especially vulnerable to low blood sugar episodes, a more cautious goal of 50% or more is recommended.
Time in range is useful because it captures the full picture: not just your average, but how much your blood sugar swings throughout the day. Two people can have the same A1C while having very different day-to-day patterns, and the one with wider swings faces more risk.
Adjusted Targets for Older Adults
Blood sugar targets loosen as people get older, particularly after age 70. Tight glucose control carries a real tradeoff: the lower you aim, the greater the chance of a dangerous low. For older adults, a hypoglycemic episode can lead to falls, confusion, and hospitalization, so guidelines intentionally allow higher numbers.
The ADA divides older adults into three groups based on overall health:
- Healthy older adults (few other medical conditions, mentally sharp): fasting goal of 90 to 130 mg/dL, A1C below 7.5%
- Complex health (multiple chronic conditions or mild cognitive decline): fasting goal of 90 to 150 mg/dL, A1C below 8%
- Very complex or poor health (long-term care, end-stage illness, or significant cognitive impairment): fasting goal of 100 to 180 mg/dL, A1C below 8.5%
These wider ranges aren’t a sign of giving up on blood sugar management. They reflect the reality that preventing a dangerous low matters more than chasing a perfect number, especially when someone has limited ability to recognize or respond to low blood sugar symptoms on their own.
What Your Reading Actually Tells You
A single blood glucose reading is a snapshot, not a verdict. Your number will be different at 7 a.m. than at 2 p.m., different after pasta than after a salad, and different on a day you walked for 30 minutes versus a day you sat at a desk. That variability is normal.
What matters most is the pattern over time. If your fasting readings are consistently in the low 80s or 90s, that’s a strong sign your metabolism is working well. If they’re creeping above 100 on most mornings, that’s worth tracking and discussing at your next checkup, even if you feel fine. Prediabetes causes no symptoms, which is exactly why the numbers matter.
For people already managing diabetes, the targets above give you a framework, but your ideal range may be personalized based on your medications, how long you’ve had diabetes, and your risk of lows. The key question isn’t whether any single reading is “good” or “bad.” It’s whether your overall trend is heading in the right direction.