Blood Sugar Log
Log a reading in seconds and see your average, estimated A1C and time in range, with patterns by meal. Saved only in this browser, with a printable report for your doctor.
Key facts
- For most adults with diabetes, the ADA suggests 80–130 mg/dL (4.4–7.2 mmol/L) before meals and under 180 mg/dL (10.0 mmol/L) 1–2 hours after starting a meal.
ExampleExample log · average, Jan 5 – Jan 18
136mg/dL
Estimated A1C about 6.4%, from 49 readings on 14 days.
before a meal or fastingafter a meal or othertarget rangenotelines break at gaps over 8 hours
- In range (70–180)
- 88%
- Lows (under 70)
- 1
- Highs (over 180)
- 5
General information from published research, not a diagnosis or medical advice. Talk to a doctor before changing medication or treatment. If a reading worries you, contact your care team. SourcesTerms
Insights
Jan 5 – Jan 18Based on 49 finger-stick readings on 14 of 14 days.
Lows: 1 low (under 70 mg/dL) in this period, at 4:10 pm on Jan 14. Talk to your care team about lows.
Going well: After lunch you stayed under 180 mg/dL on all 4 days you checked.
For context: Your readings were fairly steady: variability (CV) was 20%, within the consensus goal of 36% or less. From finger-sticks this is a rough guide.
Statistics
Changes are against the 14 days beforeTime in range
Share of your 49 readings in each band. Finger-sticks cluster around meals, so this is not the share of the day a sensor would measure.
- Very high over 250 mg/dLgoal under 5%0%0 readings
- High 181–250 mg/dLgoal under 25% with very high10%5 readings
- In range 70–180 mg/dLgoal over 70%88%43 readings
- Low 54–69 mg/dLgoal under 4% with very low2%1 reading
- Very low under 54 mg/dLgoal under 1%0%0 readings
Goals from Battelino et al., Diabetes Care 2019, for most adults with type 1 or type 2 diabetes. Older or higher-risk adults and pregnancy have different goals; your care team may set others.
Day by day
14 days · select a day to open itEach day’s lowest to highest reading, with its average as a dot.
Your readings
Your readings will appear here, newest first. They’re saved only in this browser: nothing is sent anywhere. Already have readings in Dexcom Clarity, LibreView, mySugr, Apple Health or a spreadsheet? Use Import readings in the ⋯ menu.
Your targetsRange 70–180 mg/dL
Defaults are the ADA and time-in-range consensus targets. Your care team may set different ones (for example in pregnancy, or for older adults); change them here and every number on the page follows.
How the numbers are worked outTime-in-range consensus, GMI, ADAG and ADA targets, with sources
Average is the mean of your readings in the period; variability (CV) is the standard deviation divided by the average, with 36% or less as the consensus goal. Estimated A1C uses the ADAG formula, A1C (%) = (average mg/dL + 46.7) / 28.7, and is shown once there are at least 14 readings on 7 days. With sensor (CGM) data the page shows the GMI instead: GMI (%) = 3.31 + 0.02392 × average mg/dL. Readings taken at set times can miss highs and lows in between, so compare either with a lab A1C.
Time in range uses the international consensus bands: very low under 54, low 54–69, in range 70–180, high 181–250 and very high over 250 mg/dL, with goals for most adults of over 70% in range, under 4% below 70 (under 1% below 54) and under 25% above 180 (under 5% above 250). You can switch to your own range. The consensus reads these from a sensor worn for at least 14 days, 70% of the time; with finger-sticks they are shares of readings, not of the day, so the page marks them as low confidence.
Time of day folds the period onto one 24-hour axis, as the ambulatory glucose profile (AGP) does: the median with the middle 50% (25th–75th percentiles) and 90% (5th–95th) of readings in half-hour slots, each smoothed over the slots beside it. It is drawn only when every slot has at least 5 readings on 5 or more days; otherwise each reading is shown as a dot. Lines over time break at gaps longer than 8 hours (finger-sticks) or three sensor intervals.
Targets by meal: before meals 80–130 mg/dL and under 180 mg/dL 1–2 hours after starting a meal. Meals are worked out from the time of day (breakfast before 11 am, lunch until 4 pm, dinner after), and the average rise pairs each after-meal reading with that day’s reading before the same meal, 30 minutes to 4 hours earlier. Lows: under 70 mg/dL (level 1) and under 54 mg/dL (level 2).
mmol/L = mg/dL ÷ 18.0182. This log is for keeping track, not for diagnosis or treatment decisions.
- Battelino T, et al. Clinical Targets for Continuous Glucose Monitoring Data Interpretation: Recommendations From the International Consensus on Time in Range. Diabetes Care 2019;42(8):1593–1603.
- Bergenstal RM, et al. Glucose Management Indicator (GMI): A New Term for Estimating A1C From Continuous Glucose Monitoring. Diabetes Care 2018;41(11):2275–2280.
- Nathan DM, et al. Translating the A1C Assay Into Estimated Average Glucose Values (ADAG). Diabetes Care 2008;31(8):1473–1478.
- American Diabetes Association. Standards of Care in Diabetes 2025, section 6: Glycemic Goals and Hypoglycemia.
How this works: Method, 4 sources, Checked against 4 worked examples,
How this works
Method
Your average is the mean of the readings in the period, and variability is their standard deviation divided by that average. The estimated A1C uses the ADAG formula, A1C (%) = (average mg/dL + 46.7) ÷ 28.7, once there are 14 readings on 7 days; with sensor data it shows the GMI, 3.31 + 0.02392 × average mg/dL, instead. Time in range is the share of readings in each consensus band (under 54, 54–69, 70–180, 181–250 and over 250 mg/dL), and meal targets default to the ADA’s 80–130 before and under 180 after.
Sources
- Clinical Targets for Continuous Glucose Monitoring Data Interpretation: Recommendations From the International Consensus on Time in Range (Diabetes Care, 2019)
- Standards of Care in Diabetes, section 6: Glycemic Goals and Hypoglycemia (American Diabetes Association, 2025)
- Translating the A1C Assay Into Estimated Average Glucose Values (ADAG) (Diabetes Care, 2008)
- Glucose Management Indicator (GMI): A New Term for Estimating A1C From Continuous Glucose Monitoring (Diabetes Care, 2018)
How it’s tested
4 worked examples for this page are checked by automated tests before every release: given the inputs, the tool must show the expected answer.
Limits
General information from published research, not a diagnosis or medical advice. Talk to a doctor before changing medication or treatment. If a reading worries you, contact your care team.
Privacy
You choose. Stays on your device unless you click to send something to a service you pick; the tool says which. Your readings stay in this browser. Connect Nightscout and your browser reads from your own Nightscout site. With your own AI key, insights send their facts and your question to that provider. About privacy labels
Changes
- Connecting your own Nightscout site works again: the log’s page is now allowed to reach it, and only that page.
- The insights can be worded by an AI service using your own key; only the facts and your questions are sent, never your readings.
- Rebuilt: charts over time, by time of day and by meal, GMI for sensor data, imports from Dexcom, LibreView, mySugr, Apple Health and Nightscout, and a report to share with your care team.
- Usage statistics no longer record a reading’s value, range or meal.
- Added key facts with the ADA and time-in-range targets.
- CSV import asks which unit a file uses when it doesn’t say, and lists the rows it skipped.
- First published: log readings and see your average, estimated A1C and time in range, with a printable report and blank log sheet.
Frequently Asked Questions
Where are my readings saved?
Only in this browser, on this device. Nothing is sent to Binary Decimal and readings never go into the page address. To keep a copy or move to another phone or computer, use Backup & sync (linked in the footer), or download a CSV from the ⋯ menu.
What is a normal blood sugar?
Without diabetes, fasting glucose is usually 70–99 mg/dL (3.9–5.5 mmol/L). For most adults with diabetes, the American Diabetes Association suggests 80–130 mg/dL (4.4–7.2 mmol/L) before meals and under 180 mg/dL (10.0 mmol/L) 1–2 hours after starting a meal. Your care team may set different targets, for example in pregnancy or for older adults; you can change them under “Your targets”.
How is the estimated A1C worked out, and how accurate is it?
It uses the ADAG study formula: A1C (%) = (average glucose in mg/dL + 46.7) / 28.7. It needs about two weeks of readings (at least 14 on 7 different days) before it is shown. Finger-stick readings taken at set times don’t capture the whole day, and a lab A1C reflects roughly three months, so treat it as a guide and compare it with your lab result.
What counts as low or high?
Below 70 mg/dL (3.9 mmol/L) is low and below 54 mg/dL (3.0 mmol/L) is very low (ADA level 1 and level 2 hypoglycaemia). Time-in-range guidelines treat 70–180 mg/dL (3.9–10.0 mmol/L) as the target range and above 250 mg/dL (13.9 mmol/L) as very high. If you have symptoms or readings outside your range, follow the plan from your care team.
What are time in range, GMI and the time-of-day chart?
Time in range is the share of readings between 70 and 180 mg/dL (3.9–10.0 mmol/L); the international consensus goal for most adults with diabetes is over 70%, with under 4% below 70. GMI (glucose management indicator) estimates A1C from sensor data: 3.31 + 0.02392 × average mg/dL. The time-of-day chart folds every day onto one, like the ambulatory glucose profile (AGP) clinics use, showing the median and the usual spread at each hour. These were designed for continuous glucose monitors; with a few finger-sticks a day the page still shows them but says they are low confidence.
How often should I check my blood sugar?
It depends on your treatment, so follow your care team’s advice. People using insulin often check several times a day; others may check less often, for example a fasting reading plus a reading after different meals to learn how food affects them.
Can I print a log for my doctor?
Yes. “Print report for my doctor” in the ⋯ menu prints the period you’re viewing like the one-page summaries clinics use: your statistics, the time-in-range bar, the time-of-day profile and the last 14 days, then before vs after meals and a table of every day. “Print a blank log sheet” prints a weekly paper sheet to fill in by hand.
Can I import readings from my meter or CGM?
Yes. “Import readings” in the ⋯ menu reads a Dexcom Clarity CSV, a LibreView (FreeStyle Libre) CSV, a mySugr CSV, the export.zip from Apple Health, a file exported from this log, or any CSV with a date (YYYY-MM-DD), a time and a glucose column in mg/dL or mmol/L. Files are read on your device and nothing is uploaded. You see how many readings are new before anything is saved, readings already in your log are skipped, and each one keeps where it came from. If you run Nightscout, you can also connect your own site with a read-only token to bring in new readings whenever the log opens.