A fasting blood sugar of 100 mg/dL or higher is considered above normal, and 126 mg/dL or higher on two separate tests means diabetes. But “too high” depends on when you last ate, whether you already have diabetes, and how your body is responding in the moment. Here’s how to read your numbers in context.
Normal, Prediabetes, and Diabetes Ranges
The clearest way to know if your blood sugar is too high is to compare it against the standard diagnostic thresholds, which are based on fasting levels (meaning you haven’t eaten for at least eight hours):
- Normal: below 100 mg/dL
- Prediabetes: 100 to 125 mg/dL
- Diabetes: 126 mg/dL or higher
A single high reading doesn’t automatically mean diabetes. The diagnosis typically requires a second confirmatory test. However, if a random blood sugar check (taken at any time, regardless of meals) comes back at 200 mg/dL or higher and you’re experiencing symptoms like excessive thirst or frequent urination, that alone can confirm diabetes.
After-Meal Blood Sugar Targets
Blood sugar naturally rises after eating and peaks roughly one to two hours later. In people without diabetes, it stays below 140 mg/dL even after a meal. If your post-meal readings regularly exceed that, your body may not be processing glucose efficiently.
For people already managing diabetes, the target is more relaxed. The American Diabetes Association recommends keeping post-meal blood sugar below 180 mg/dL. This higher ceiling exists because tight control increases the risk of blood sugar dropping too low, which can be just as dangerous as a high reading. Your personal target may differ based on your treatment plan, age, and overall health.
What A1C Tells You About Average Levels
A1C measures your average blood sugar over roughly three months. It’s reported as a percentage, and each point corresponds to a specific average glucose level:
- A1C of 6%: average blood sugar of about 126 mg/dL
- A1C of 7%: average of about 154 mg/dL
- A1C of 8%: average of about 183 mg/dL
- A1C of 9%: average of about 212 mg/dL
- A1C of 10%: average of about 240 mg/dL
An A1C below 5.7% is normal. Between 5.7% and 6.4% signals prediabetes, and 6.5% or higher indicates diabetes. Most adults with diabetes aim to keep their A1C below 7%, though this isn’t universal.
Targets Shift for Older Adults
Blood sugar goals for people over 65 are deliberately set higher than for younger adults. Tight glucose control in older adults raises the risk of dangerous low blood sugar episodes, which can cause falls, confusion, and hospitalization.
For healthy older adults, a reasonable A1C target is below 7.5%, with fasting levels between 140 and 150 mg/dL. Older adults with multiple health conditions may aim for an A1C of 8% or lower, with fasting levels between 160 and 170 mg/dL. For those in poor health or with cognitive decline, an A1C up to 8.5% (corresponding to an average glucose around 200 mg/dL) may be appropriate, with the primary focus on avoiding both severe highs above 350 mg/dL and dangerous lows.
How High Blood Sugar Feels
Mildly elevated blood sugar often produces no symptoms at all, which is why many people with prediabetes don’t realize anything is wrong. As levels climb higher, your kidneys start working overtime to flush excess glucose into your urine, pulling water along with it. This is why the earliest noticeable symptoms tend to be increased thirst and frequent urination. You may also notice headaches and blurred vision.
When blood sugar stays elevated over weeks or months, additional signs appear: persistent fatigue, unexplained weight loss, slow-healing cuts, recurring skin or yeast infections. These signal that your body has been running at above-normal glucose levels for a sustained period, not just a single spike after a big meal.
When High Blood Sugar Becomes Dangerous
A reading above 240 mg/dL is a signal to check for ketones, which are acids that build up in your blood when your body starts burning fat instead of glucose for energy. You can check ketones with a simple urine test strip available at most pharmacies. Ketone buildup can progress to a life-threatening condition called diabetic ketoacidosis, which is diagnosed when blood sugar exceeds 200 mg/dL alongside high ketone levels and acidic blood chemistry. Symptoms include nausea, vomiting, abdominal pain, and a fruity smell on your breath.
At the extreme end, blood sugar above 600 mg/dL can trigger a condition called hyperosmolar hyperglycemic state, where the blood becomes dangerously concentrated. This is most common in older adults with type 2 diabetes and develops over days or weeks of sustained very high glucose. It can cause confusion, seizures, and coma. Both emergencies require immediate medical treatment.
Exercise and High Blood Sugar
Physical activity normally helps bring blood sugar down, but there’s an important exception. If your blood sugar is above 250 mg/dL, exercise can actually make things worse. At that level, your body may not have enough insulin to move glucose into your cells, so your liver responds to the physical demand by releasing even more glucose into your bloodstream. If you check your level before a workout and it’s over 250, wait until it comes down before exercising.
Below that threshold, moderate activity like walking, cycling, or swimming is one of the most effective ways to lower blood sugar after a meal. Muscles use glucose directly during movement, often producing a noticeable drop within 30 to 60 minutes.