Normal Fasting Blood Sugar

Fasting blood sugar measures glucose after at least 8 hours without eating or drinking anything but water — typically first thing in the morning, before breakfast.

Normal Fasting Blood Sugar Range

A fasting blood sugar below 100 mg/dL is considered normal. Between 100 and 125 mg/dL falls in the prediabetes range, and 126 mg/dL or higher — confirmed on a repeat test — meets the diagnostic threshold for diabetes.

Why This Test Is Used So Often

Fasting blood sugar is one of the simplest and most common ways diabetes and prediabetes are screened for, since it requires only a single blood draw and doesn't need the multi-hour process an oral glucose tolerance test involves. It's often ordered alongside or instead of an HbA1c test.

What Can Affect the Result

Illness, stress, certain medications (including steroids), and not truly fasting (even black coffee or gum can matter for some people) can all shift a fasting result. This is part of why a single elevated reading is usually confirmed with a repeat test before a diagnosis is made — see our Diabetes Blood Tests guide for how the different tests compare.