Internal Medicine
Normal Fasting Blood Sugar
Reviewed by the JordanMedHub Medical Editorial Team · 9/12/2026
Quick Answer
Fasting blood sugar is one of the most common ways diabetes and prediabetes are diagnosed. Here's what counts as normal, and what a higher result means.
In this article
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.
Disclaimer
This guide is for general education only and does not diagnose or recommend treatment for any individual. If your fasting blood sugar is outside the normal range, talk to a doctor about what it means and whether further testing is needed.
Frequently Asked Questions
How many hours should I fast before a fasting blood sugar test?
At least 8 hours, with water allowed. Most people schedule the test first thing in the morning after an overnight fast.
Can stress raise fasting blood sugar?
Yes — physical or emotional stress can temporarily raise blood sugar through stress hormones, which is one reason an isolated high reading is usually retested rather than treated as final.
Written by JordanMedHub Medical Editorial Team
Updated 9/12/2026
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