Normal Blood Sugar Levels: Targets, Checks and CGM Explained

Normal blood sugar levels in adults without diabetes are a fasting glucose below 100 mg/dL (5.6 mmol/L) and an A1C below 5.7% (39 mmol/mol). Above those numbers, the American Diabetes Association (ADA) defines ranges for prediabetes and diabetes. If you already have diabetes, your own targets depend on your treatment and on where you live.

The tables below give every figure in both mg/dL and mmol/L, so you can read them whichever meter you use. This guide is general education. If you use insulin or other glucose medicines, follow the plan your diabetes team gave you.

What are normal blood sugar levels?

The ADA uses three tests to define prediabetes and diabetes: A1C, fasting plasma glucose and a 2 hour glucose tolerance test. Fasting means no food or calorie-containing drinks for at least 8 hours.^[1] Results below the prediabetes range are counted as normal.

A single result is usually not enough for a diagnosis. Your doctor will normally confirm it with a repeat or a second test.^[1] Our guide to the HbA1c test explains what A1C measures.

What targets apply if you have diabetes?

In the US, the ADA says an A1C below 7% (below 53 mmol/mol) is appropriate for many nonpregnant adults. It suggests 80 to 130 mg/dL (4.4 to 7.2 mmol/L) before meals and below 180 mg/dL (below 10.0 mmol/L) at the peak after a meal. It also notes that goals may be more or less strict for some people.^[2]

For CGM users, the ADA measures time in range, meaning the share of the day spent between 70 and 180 mg/dL (3.9 to 10.0 mmol/L). For most adults it suggests more than 70% of the day in range, less than 25% above 180 mg/dL (10.0 mmol/L) and less than 4% below 70 mg/dL (3.9 mmol/L). For older adults with complex health needs the ADA allows more time above range but less time below 70 mg/dL (3.9 mmol/L).^[2]

In the UK, NICE suggests an HbA1c of 48 mmol/mol (6.5%) for adults with type 2 diabetes managed by lifestyle or by a medicine that does not cause hypos, and 53 mmol/mol (7.0%) for those on a medicine that can.^[3] Diabetes UK points out that NICE has no day to day blood sugar targets for type 2 diabetes and advises agreeing your own with your healthcare team.^[4]

When is blood sugar too low or too high?

The ADA classes a glucose reading below 70 mg/dL (3.9 mmol/L) as hypoglycaemia, or low blood sugar. It sorts lows into three levels:^[2]

• Level 1: below 70 mg/dL (3.9 mmol/L) but not below 54 mg/dL (3.0 mmol/L).
• Level 2: below 54 mg/dL (3.0 mmol/L). The ADA says a low at this level needs immediate action.
• Level 3: a severe low in which a person's mental or physical state changes and they need another person's help to recover, whatever the reading.

For high readings, the ADA's CGM goals use two thresholds. Time above 180 mg/dL (10.0 mmol/L) counts as level 1 hyperglycaemia and time above 250 mg/dL (13.9 mmol/L) as level 2. For most adults it suggests less than 25% and less than 5% of the day at those levels.^[2] If you get high readings often, or a high reading comes with feeling unwell, contact your healthcare team.

Low blood sugar is most common if you use insulin or a sulfonylurea such as gliclazide or glimepiride.^[6] Low blood sugar usually means below 4 mmol/L (72 mg/dL) in the UK or below 70 mg/dL (3.9 mmol/L) in the US.^[6][2] Our guide to low blood sugar covers the warning signs. In the UK, the NHS says to call 999 if someone may have very low blood sugar and is not responding normally or is unconscious, and a glucagon injection is not available or you do not know how to use it, or they have not recovered within 10 minutes of a glucagon injection, or they have been drinking alcohol.^[6] In the US, the ADA says to call 911 right away if someone is unconscious and glucagon is not available or no one knows how to use it.^[2]

How often should I check my blood sugar?

It depends on your treatment. For A1C, the ADA advises a check at least twice a year, and about every 3 months if you are not at goal or your treatment has changed.^[2] Diabetes UK says most people have the test every three to six months and are entitled to it at least once a year.^[7]

Finger-prick checks are a different question. NICE advises against routinely offering them to adults with type 2 diabetes unless they take insulin, have had hypos, take tablets that raise the risk of a hypo while driving or using machinery, or are pregnant or planning a pregnancy.^[3]

A trial of 450 adults with type 2 diabetes who did not use insulin found no meaningful difference in A1C or quality of life after 1 year between people who did finger-prick checks and people who did not.^[8]

The ADA adds that checks can still help when you are changing your meals, activity or medicines, especially medicines that can cause a low.^[5]

Blood sugar after eating: what should it be?

For many adults with diabetes, the ADA suggests a peak below 180 mg/dL (below 10.0 mmol/L). Measure it 1 to 2 hours after the start of the meal, which is when glucose usually peaks in people with diabetes.^[2] UK advice is set by your own team. For more on keeping meals steady, see our guides to foods that keep blood sugar stable and exercise and blood sugar.

CGM vs finger prick: which is more accurate?

They measure different things. A finger-prick meter tests blood. A CGM measures glucose in the fluid just under the skin. The ADA says this tracks blood glucose well but can lag when glucose is rising or falling quickly.^[5]

Studies put that delay at about 5 to 10 minutes. In healthy adults it averaged 5.3 to 6.2 minutes.^[9] In adults with type 1 diabetes the median was 6.8 minutes, and all readings had caught up by 9.8 minutes.^[10] In a study of one CGM model in 316 adults, the average gap from lab values was 8.2% for sensors on the arm and 9.1% on the abdomen. The study was funded by Dexcom, the maker, and four authors were Dexcom employees.^[11]

The ADA also says meters differ in accuracy, so the brand matters too.^[5] Read more in our guide to diabetes technology.

How do I take an accurate finger-prick reading?

1. Follow the instructions for your own meter and in-date test strips, and wash and dry your hands before testing.^[5]
2. Let the meter settle after heat or cold. In a lab test, meters took 15 to 30 minutes to give stable readings after being moved back to room temperature.^[12]
3. If your hands are cold, the CDC suggests warming them near a heater or around a cup of warm water before testing.^[13]
4. If a reading does not match how you feel, check again and contact your care team if you are unsure.^[5][6]

If you are on insulin or a sulfonylurea such as gliclazide or glimepiride, learn the low blood sugar signs and what to do about them.^[6]

Questions to ask your diabetes team

• What fasting and after-meal blood glucose targets fit my age, health and medicines?^[2][3]
• What is my personal HbA1c target, and how often should we check it?^[2][3]
• Do I need to check my blood glucose at home, and how many times a day?^[3][5]
• Do any of my medicines, such as insulin or gliclazide, mean I need a plan for readings below 4 mmol/L (72 mg/dL) or 70 mg/dL (3.9 mmol/L)?^[6][2]

Frequently asked questions

What are normal blood sugar levels for adults?

Without diabetes, a fasting glucose below 100 mg/dL (5.6 mmol/L) and an A1C below 5.7% (39 mmol/mol) are in the normal range, based on ADA criteria.^[1]

What is a good A1C for someone with diabetes?

The ADA suggests below 7% (53 mmol/mol) for many nonpregnant adults. In the UK, NICE suggests 48 mmol/mol (6.5%), or 53 mmol/mol (7.0%) for people on a medicine that can cause hypos. Your own target may differ.^[2][3]

Do I need to check my blood sugar every day with type 2 diabetes?

Not always. NICE advises against routinely offering finger-prick checks to adults with type 2 diabetes unless they take insulin, have had hypos, take tablets with a hypo risk while driving or using machinery, or are pregnant or planning a pregnancy. Ask your team what applies to you.^[3]

Is a CGM more accurate than a finger prick?

A CGM reads fluid under the skin rather than blood. Studies in small groups of adults found the fluid trails blood by about 5 to 10 minutes, and the ADA says the gap can be larger when glucose is rising or falling quickly. Both methods have some error, and accuracy varies by device.^[5][9][10]

Where to go next

For more on normal blood sugar levels and what your own numbers mean, these guides go further:

• The HbA1c test, for what your 3 month average shows.
• Diabetes technology, for CGMs, pumps and apps.
• Is Diabec legit, for the company details and the cautions for each herb if you take glucose medicine.

Note: If you are pregnant, breastfeeding, or considering giving any supplement or herbal product to a child, consult your healthcare provider before making any changes to your diet, supplement routine, or prescribed medications.

Disclaimer: These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure, or prevent any disease. Talk to your doctor before changing your diet, your activity or your medicines, and before starting any supplement.