When to Check Your Blood Sugar: Before and After Meals, Bedtime

The usual testing times

When	What it tells you
On waking (fasting)	How your body and your long-acting medicine handled the night.
Before a meal	Where you start from. If you use mealtime insulin, it helps decide the dose.
1 or 2 hours after a meal	How much that meal raised your blood sugar. Count from the start of the meal.
Bedtime	Whether you are going to sleep at a safe level.
Extra checks	Before driving, around exercise, when you feel low, when you are ill.

If you use insulin several times a day

People on mealtime and long-acting insulin usually test the most. The UK NICE guideline for adults with type 1 diabetes who use a finger-prick meter advises testing at least 4 times a day, including before each meal and before bed, and up to 10 times a day in some situations: before driving, during illness, around sport, during pregnancy, or when lows are frequent. The American Diabetes Association lists similar moments: on waking, before meals and snacks, at bedtime, before exercise, when you suspect a low, after treating a low until you are back in range, and before driving.

Many people with type 1 diabetes now use a continuous glucose monitor. A log is still useful for doses, food and notes.

If you have type 2 diabetes

How often you test depends on your medicine. NICE advises against routine self-testing for most adults with type 2 diabetes who do not use insulin. It does recommend testing if you take insulin, if you take medicine that can cause lows (such as sulfonylureas) and you drive or operate machinery, if you have had lows, if you are pregnant or planning a pregnancy, or to check a suspected low.

If your doctor has asked you to test, a common pattern is a few checks a day, or before and after one meal a day, changing which meal over the week. A before-and-after meal log helps you see which meals raise your sugar most.

If you have gestational diabetes

NICE advises women with gestational diabetes who manage it with diet and exercise or tablets to test fasting and 1 hour after each meal every day. Those on several insulin injections a day also test before meals and at bedtime. Some clinics ask for 2 hours after meals instead of 1. Use the timing your clinic gave you.

Timing the after-meal check

Count from when you start eating, not when you finish.
Use the same timing every time, so the readings can be compared.
Set a timer on your phone when you sit down to eat. It is easy to forget otherwise.

The extra checks

Before driving, if you use insulin or medicine that can cause lows. Many countries have legal rules on this.
Before, during and after exercise, especially longer or harder sessions.
When you feel low: shaky, sweaty, hungry, confused. Test, treat, and test again.
When you are ill. Illness can raise blood sugar even when you eat less. Ask your team for sick-day rules.

Add a spare column to your log for these checks, so they do not end up squeezed into the margin.

Not medical advice. This guide is general information. Your targets, testing times and treatment come from your doctor, diabetes nurse or clinic, who know your situation.

Make a log with your testing timesRename, add or remove columns to match the times you test.

Questions

Is fasting blood sugar the same as before breakfast?

Usually, yes. Fasting means at least 8 hours without food, which for most people is first thing in the morning, before breakfast.

Should I test 1 hour or 2 hours after eating?

Both are used. NICE uses 1 hour in pregnancy and at least 90 minutes after eating for adults with type 1 diabetes. The ADA uses 1 to 2 hours after the start of the meal. Ask your clinic which they prefer and stick to it.

How many times a day should I test?

It depends on your treatment. People on several insulin injections a day often test 4 or more times a day. Many people with type 2 diabetes not on insulin do not need to test every day. Your doctor or nurse can tell you what fits you.

Do I need to test if I use a continuous glucose monitor?

Most of the time the sensor replaces finger-pricks, but you may still need a finger-prick test when your symptoms do not match the sensor reading or when the sensor asks for one. Follow the instructions for your device.

When to check your blood sugar