Meal spike checker
Your spike is your highest reading after the meal minus your reading just before it. “Back to baseline” here means back within 10 mg/dL (0.6 mmol/L) of where you started, or within a fifth of the rise for bigger rises. Rises after meals are normal: adults without diabetes spent about 3 hours a day above 140 mg/dL in the Framingham study (Spartano et al. 2024).
After the first bite
One meal on one day says little: in a study of adults without diabetes, the same meal eaten twice, about a week apart, often gave quite different rises (Hengist et al. 2024). Compare the same meal on a few days.
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How it is worked out
Rise = highest reading after the meal − reading before Back near baseline = first reading after the peak at or under before + max(10 mg/dL, rise ÷ 5)
The same rule the free CGM report uses for your biggest rises. Times count from the first bite. A sensor reads fluid under the skin and trails a finger-prick by roughly 5 to 15 minutes, so the peak it shows comes a little late.
Sources
- Spartano et al. 2024. Journal of Clinical Endocrinology & Metabolism. CGM in the Framingham Heart Study.
- Hengist et al. 2024. American Journal of Clinical Nutrition. Meal responses on two sensors at once.
Glucose tools
See it all from your export
The free CGM report reads the whole file: your 24-hour profile (AGP), time in range, GMI, variability, your biggest rises and overnight sensor pressure.
Open the free CGM reportQuestions people ask
- How do I work out my glucose spike after a meal?
- Take your reading just before you eat, then your highest reading in the next 2 to 3 hours, and subtract. From 90 to 150 mg/dL (5.0 to 8.3 mmol/L) is a rise of 60 mg/dL (3.3 mmol/L). Enter your readings above to see the peak time and when you were back near where you started.
- How long should glucose take to go back down after eating?
- There is no single number: it depends on the meal, the person and the day. The checker above shows when your own readings got back near where they started. Track the same meal on a few days rather than judging one curve.
- Is a glucose spike after eating bad?
- Rises after meals are normal. Adults without diabetes in the Framingham study spent about 3 hours a day above 140 mg/dL (Spartano et al. 2024). Whether smaller spikes improve health in people without diabetes is still being studied. Use the number to learn what moves you, not to score a food for good.
- How high should blood sugar go after a meal if I don’t have diabetes?
- There is no agreed CGM cut-off. Rises to around 140 mg/dL (7.8 mmol/L) after a meal are common in adults without diabetes, and higher peaks happen too: in the Framingham study they spent about 3 hours a day above 140 mg/dL (Spartano et al. 2024). Diabetes is judged on fasting glucose, HbA1c or a lab glucose tolerance test (under 140 mg/dL two hours after the drink is normal), not on a sensor’s peak. If your readings worry you, ask your doctor about those tests.
More free glucose tools
Information, not a diagnosis. HealthOS is a wellness product, not a medical device: these numbers can’t tell you whether anything needs treatment. Talk to a doctor about your results.