For most adults, a blood sugar reading above 180 mg/dL after a meal or above 130 mg/dL before a meal is considered too high. But “too high” depends on context: whether you have diabetes, when you last ate, and what you’re planning to do next. A single elevated reading isn’t the same as chronically high levels, and the thresholds for concern shift depending on the situation.
Normal Blood Sugar vs. Too High
In people without diabetes, blood sugar stays in a surprisingly tight range. Continuous glucose monitoring studies show that healthy individuals spend over 99% of the day below 140 mg/dL. After a meal, blood sugar typically peaks around 130 to 135 mg/dL within about 46 to 50 minutes, then drops back to baseline. The average glucose across the full day in healthy subjects hovers around 95 mg/dL.
For people managing diabetes, the CDC lists these typical targets: 80 to 130 mg/dL before a meal, and less than 180 mg/dL two hours after the start of a meal. Anything consistently above those ranges signals that blood sugar is running too high and management needs adjusting. Your individual targets may differ based on age, other health conditions, and how long you’ve had diabetes.
The Diagnostic Thresholds
If you don’t have a diabetes diagnosis, your A1C percentage (a measure of average blood sugar over the past two to three months) tells you where you stand:
- Normal: below 5.7%
- Prediabetes: 5.7% to 6.4%
- Diabetes: 6.5% or above
A fasting blood sugar of 100 to 125 mg/dL falls in the prediabetes range. At 126 mg/dL or higher on two separate tests, the diagnosis is diabetes. These numbers matter because they mark the point where chronically elevated glucose begins to raise your risk of damage to blood vessels, nerves, eyes, and kidneys over time.
When Symptoms Start
Many people with diabetes don’t feel any different until blood sugar climbs above 250 mg/dL. At that point, the classic symptoms tend to appear: excessive thirst, frequent urination, headaches, and blurred vision. People who haven’t been diagnosed with diabetes often notice symptoms at lower levels, because their bodies aren’t accustomed to elevated glucose.
This gap between “too high on paper” and “too high to feel” is part of what makes chronic hyperglycemia dangerous. Blood sugar can sit at 200 mg/dL for weeks or months without obvious symptoms, quietly contributing to long-term complications. That’s why regular testing matters more than waiting for your body to sound the alarm.
The 250 mg/dL Checkpoint
At 250 mg/dL, the situation escalates. The Joslin Diabetes Center recommends testing for ketones anytime blood sugar stays above 250 mg/dL for two consecutive readings. Ketones are acids your body produces when it starts burning fat instead of glucose for fuel, and high levels can push you toward a dangerous condition called diabetic ketoacidosis (DKA).
This threshold also affects exercise decisions. If your blood sugar is above 250 mg/dL and you have moderate or high ketone levels, you should not exercise. Physical activity can actually push blood sugar higher in that situation rather than bringing it down. Even without ketones, caution is recommended when starting exercise above 300 mg/dL.
Emergency-Level Blood Sugar
Blood sugar above 250 mg/dL combined with ketones in the blood or urine meets one of the key criteria for DKA. This is most common in type 1 diabetes but can occur in type 2 as well. Other signs include nausea, vomiting, abdominal pain, fruity-smelling breath, and rapid breathing. DKA requires emergency treatment.
At 300 mg/dL and above, the risk climbs sharply. Another emergency, hyperosmolar hyperglycemic state, can develop when blood sugar reaches extremely high levels (often above 600 mg/dL), typically in type 2 diabetes. It causes severe dehydration and confusion and can be life-threatening without hospital care.
Worth noting: DKA can occasionally occur even when blood sugar is below 250 mg/dL, particularly in people taking certain diabetes medications or those with alcohol use disorder. Symptoms like nausea, vomiting, and rapid breathing should be taken seriously regardless of the number on the meter.
What To Do When Your Reading Is High
If your blood sugar is moderately elevated, in the 180 to 250 mg/dL range, a few immediate steps can help. Drinking water is one of the most effective, because your kidneys filter excess sugar out through urine, and staying hydrated supports that process. Light physical activity like walking can also help bring levels down, as long as you’re under 250 mg/dL and don’t have ketones.
Cutting back on carbohydrates at your next meal or snack gives your body less glucose to process. If you take insulin, follow whatever correction protocol your care team has given you. Avoid sugary drinks, which will push levels higher.
If your blood sugar is consistently above 200 mg/dL, that pattern points to something that hydration and a walk won’t fix on their own. It often means your medication, insulin dose, or overall management plan needs an adjustment.
Targets Shift for Older Adults
For older adults, the American Diabetes Association recommends that blood sugar targets be individualized and sometimes relaxed. The reasoning is practical: tighter glucose control increases the risk of hypoglycemia (dangerously low blood sugar), which can cause falls, confusion, and hospitalization in older people. For someone with multiple health conditions or limited life expectancy, the harm from a low blood sugar event can outweigh the long-term benefit of keeping numbers below 130 mg/dL before meals. In these cases, a higher target range is appropriate and intentional, not a failure of management.
Quick Reference by Level
- Under 140 mg/dL (after meals): Normal range for people without diabetes
- 130 to 180 mg/dL: Typical target zone for managed diabetes, depending on timing
- Over 180 mg/dL (after meals): Above target for most people with diabetes
- Over 250 mg/dL: Test for ketones, avoid exercise if ketones are present
- Over 300 mg/dL: Exercise with caution even without ketones, contact your care team
- Over 600 mg/dL: Medical emergency territory