How to Keep a Blood Sugar Log

To keep a blood sugar log, write down every reading from your glucose meter together with the date, the time, and what was going on — fasting, before a meal, two hours after, bedtime — plus a short note when something unusual happened. Do it right after each check, keep the same unit throughout, and bring the log to your appointments. That is the whole method; the rest of this guide is about making it stick.

The CDC, the American Diabetes Association and the NIDDK all say the same thing about self-checks: record the result, and note what might have affected it. Whether you use paper or an app is up to you.

What is a blood sugar log?

A blood sugar log (also called a glucose log, blood glucose diary or logbook) is a running record of the readings you take with your meter or continuous glucose monitor. Each entry captures one reading and the context around it. Over days and weeks the entries add up to a picture that a single reading can never show: what your mornings usually look like, how a typical dinner plays out, whether the same time of day is repeatedly high or low.

The ADA puts it bluntly: “The logging of your results is vital.” When you bring the log to your healthcare professional, they see how your body responded to your care plan between visits rather than a snapshot from the waiting room.

What to write in a blood sugar log

The NIDDK recommends recording the date and time of each self-check, the result, and other information such as what you ate or what physical activity you did. In practice a useful entry has five parts.

1. Date and time

Both, every time. Patterns only appear when readings can be lined up by time of day across several days. “Tuesday morning” is not enough; “Tue 7:10 am” is.

2. The reading and its unit

Copy the number exactly as the meter shows it. In the United States meters report in mg/dL; in most other countries the unit is mmol/L. Pick one unit for the whole log and write it once at the top. If a report or a relative's meter uses the other unit, run it through the mmol/L to mg/dL converter before you write it down, so the column stays comparable.

3. Context: when in the day, and relative to food

A reading taken before breakfast and one taken two hours after lunch mean different things, so the log has to say which it was. The contexts that healthcare professionals commonly ask about — and that the CDC lists as typical times to check — are waking (before eating or drinking), before a meal, about two hours after a meal, and bedtime. Tag each entry with one of these rather than leaving it to memory.

4. Notes

The ADA suggests noting factors that may have affected a result, such as food, activity and stress. Keep notes short and factual: “birthday cake”, “walked 40 min”, “slept badly”, “forgot morning dose”. You are not interpreting anything — you are giving your care team the context they need to interpret it with you.

5. Your target range, from your care team

Write the target range your doctor or diabetes educator gave you at the top of the log. Not a range from the internet — yours. It makes the log self-explanatory when someone else reads it, and it keeps you from second-guessing every number against whatever you last read online.

Why a regular log helps

The ADA recommends looking at your record for readings that are too high or too low several days in a row at about the same time of day — the kind of pattern that might mean your care plan needs adjusting. You cannot see that pattern in a meter's memory scrolled through one value at a time, and you certainly cannot see it in your head. The CDC adds that monitoring helps your health care team make decisions about your diabetes care plan, and that your doctor will tell you when and how often to check.

There is also a quieter benefit. A log turns “I think my mornings have been higher lately” into something you can put on the table, which makes the appointment about the data rather than about recollection.

Paper log vs digital log

The CDC notes that most meters store results, that some can send them to a phone app, and that a written record works fine if you prefer not to use a phone. Neither approach is more correct; they trade different things.

Many people mix the two: paper at home on the fridge, the app when travelling, or paper for a couple of weeks and then a switch to an app once the habit exists. If paper suits you, the free printable blood sugar log sheet has daily, weekly, monthly and large-print layouts with all five fields above already laid out.

How to keep a blood sugar log in DiabetLog

DiabetLog is a logging app, not a measuring device: it stores the readings you take with your own meter and works as a digital diabetes logbook on iPhone, iPad and Android. Keeping the log looks like this.

1. Add the reading. Type the value exactly as your meter shows it.
2. Tag the context. Choose the time of day and a tag such as fasting, so the entry is comparable with others taken at the same point in the day.
3. Set reminders for the times your care team asked you to check. The app nudges you; the schedule itself comes from your healthcare professional, not the app.
4. Enter your target range. Use the range your doctor gave you. Charts then show which readings fell inside or outside it.
5. Before an appointment, create a PDF report. Premium users can export their history as a PDF and send it by email or message, or simply show the charts on the phone.

Readings stay on your device; there is no account and nothing is uploaded. On iPhone you can optionally sync readings with Apple Health.

Tips for making the log stick

• Log immediately. The reading written from memory an hour later is the one that ends up wrong.
• Keep the log where the meter is. Same drawer, same bag, or the same phone you already carry.
• Don't skip the “bad” readings. A log with the high and low values removed tells your care team nothing. The ADA notes that numbers often trigger strong feelings; the log is a record of how the plan is working, not a grade.
• Fill gaps honestly. If you missed a week, leave it blank and carry on. A gap is information too.
• Review it before, not during, the appointment. Two minutes with the log beforehand and you arrive with questions instead of leaving with them.

If you want a concrete picture of what all this looks like on the page, the 7-day blood sugar log example walks through a filled-in sample column by column.