Calculator inputs
Example data table
| Case | Reading | Hours fasted | Converted mmol/L | Category | Comment |
|---|---|---|---|---|---|
| Case A | 92 mg/dL | 10 | 5.11 | Normal fasting range | Falls below 100 mg/dL after a valid fast. |
| Case B | 108 mg/dL | 9 | 6.00 | Prediabetes range | Above normal, but below the diabetes threshold. |
| Case C | 132 mg/dL | 8 | 7.33 | Diabetes range | Needs clinician review and lab confirmation. |
| Case D | 5.3 mmol/L | 11 | 5.30 | Normal fasting range | Equivalent to 95.4 mg/dL. |
Formula used
Fasting classification is based on standard fasting plasma glucose thresholds after at least 8 hours of fasting.
- Normal fasting range: less than 100 mg/dL
- Prediabetes range: 100 to 125 mg/dL
- Diabetes range: 126 mg/dL or higher
How to use this calculator
- Enter your current fasting blood sugar value and choose the correct unit.
- Add fasting hours. Use at least 8 hours for fasting interpretation.
- Select whether the value came from a lab, meter, or CGM.
- Optionally enter a previous reading to calculate change and trend.
- Set a preferred target range in the same unit as the current reading.
- Press the calculate button to show the result above the form.
- Review the Plotly chart, target check, converted values, and classification.
- Use CSV or PDF export to save the result summary for records.
Important interpretation notes
A fasting result is most meaningful when no calories were consumed for at least 8 hours. Water is generally acceptable.
A single high reading can be important, but symptoms, medications, illness, stress, and testing method can affect results.
Seek urgent medical care for severe symptoms, very high readings, confusion, vomiting, or trouble breathing.
FAQs
1) What is a fasting blood sugar test?
It measures blood glucose after an overnight fast. It is commonly used to screen for normal fasting glucose, prediabetes, and diabetes-range results.
2) How long should I fast before using this result?
A fasting interpretation usually needs at least 8 hours without calories. Water is generally allowed, but follow your clinician’s instructions for lab preparation.
3) What is considered a normal fasting blood sugar?
A fasting plasma glucose below 100 mg/dL is generally considered normal. This calculator also converts that value into mmol/L for convenience.
4) What range suggests prediabetes?
A fasting reading from 100 to 125 mg/dL falls into the prediabetes range. It signals higher-than-normal glucose and deserves follow-up care.
5) What range suggests diabetes?
A fasting reading of 126 mg/dL or higher is in the diabetes range. A clinician typically confirms diagnosis with repeat or additional testing.
6) Can I use a home meter reading for diagnosis?
No. Home meters help with monitoring and trend awareness, but diagnosis should rely on proper lab testing and professional interpretation.
7) Why does this calculator show mg/dL and mmol/L?
Different regions and labs use different units. Showing both makes your reading easier to compare across reports, devices, and medical discussions.
8) Should I worry about one high reading?
One high result can matter, but it does not tell the whole story. Illness, stress, sleep, and technique can influence readings, so follow up appropriately.