The short answer: blood sugar is the amount of glucose in your blood right now, while A1C is the percentage of your hemoglobin with glucose attached, which reflects your average over about 2 to 3 months. They’re linked. An A1C of 7% matches an average blood sugar of about 154 mg/dL (8.6 mmol/L), according to the American Diabetes Association.
If you need the ranges for a single reading, such as fasting or after a meal, our guide to normal blood sugar levels has them in one chart.
Is blood sugar the same as A1C?
Blood sugar and A1C aren’t the same, but they measure the same thing over different spans of time. A finger-stick meter or a continuous glucose monitor (CGM) shows your glucose at one moment. The A1C test looks at your red blood cells. Glucose sticks to hemoglobin, the protein in those cells, and the more glucose there is, the more sticks. Red blood cells are renewed about every 3 months, so the A1C reflects roughly the last 2 to 3 months, the ADA explains.
The ADA compares it to a basketball player’s shooting percentage. One game tells you how that night went. The season percentage tells you how the player is really doing. NIDDK adds that the most recent 30 days count the most.
| Blood sugar reading | A1C | |
|---|---|---|
| What it measures | Glucose in your blood now | Percentage of hemoglobin with glucose attached |
| Time covered | One moment | About 2 to 3 months |
| Fasting needed? | For a fasting test, yes (8+ hours) | No |
| Where it’s done | Home meter, CGM or lab | Lab or clinic |
| Shows highs and lows? | Yes | No |
| Diabetes cutoff | Fasting 126 mg/dL or above | 6.5% or above |
Sources for the table: the ADA, the CDC and NIDDK.
How does A1C convert to blood sugar?
A1C converts to an estimated average glucose (eAG) with a simple formula: eAG in mg/dL = 28.7 × A1C − 46.7. It comes from the ADAG study, which compared A1C with thousands of glucose readings in 507 people. The link was strong, and it didn’t differ by age, sex, diabetes type, race or ethnicity, or smoking. The ADA publishes this chart:
| A1C | Estimated average glucose (mg/dL) | Estimated average glucose (mmol/L) |
|---|---|---|
| 5% | 97 | 5.4 |
| 6% | 126 | 7.0 |
| 7% | 154 | 8.6 |
| 8% | 183 | 10.2 |
| 9% | 212 | 11.8 |
| 10% | 240 | 13.4 |
| 11% | 269 | 14.9 |
| 12% | 298 | 16.5 |
Source: American Diabetes Association Standards of Care 2025, Table 6.1. Each 1% step in A1C adds about 29 mg/dL to the average. To check your own number, multiply your A1C by 28.7 and take away 46.7. An A1C of 6.5% works out to about 140 mg/dL.
Don’t expect the eAG to match your meter. NIDDK says it won’t, because you check at certain times of day while the A1C covers every hour, including the night.
Why is my A1C high when my glucose is normal?
Your A1C can be high while your glucose readings look normal because the readings miss part of the day, or because something is affecting the A1C itself. The ADA lists three common reasons the two don’t agree:
- Your glucose swings a lot. Spot checks before meals can look fine while highs after meals or overnight go unseen.
- The meter or CGM is off. The ADA lists an inaccurate meter or CGM as one cause of a mismatch.
- The A1C is off. Some health conditions change how long red blood cells live, which changes the result.
If your numbers don’t line up, bring your meter log or CGM report to your next appointment. Your doctor may compare it with a lab glucose test, or suggest wearing a professional CGM for about 2 weeks, which the ADA describes as an option.
Can A1C be wrong?
A1C can be wrong, or at least misleading, in some people. NIDDK says iron-deficiency anemia can make it falsely high. Cleveland Clinic says kidney failure, sickle cell disease and hemolytic anemia can make it falsely low. The ADA adds pregnancy, recent blood loss or a transfusion, G6PD deficiency, medicines that boost red blood cell production, and end-stage kidney disease.
Hemoglobin variants matter too. NIDDK says the common ones (HbS, HbC, HbD and HbE) are more frequent in people of African, Mediterranean or Southeast Asian descent. Having one doesn’t raise your risk of diabetes, and most US labs use tests that work for people who carry one copy of a common variant, the ADA says. In people with sickle cell disease (HbSS) or HbEE, A1C can’t be used at all.
Even a perfect test has a little wobble. NIDDK gives an example: an A1C of 6.8% could come back anywhere from 6.4% to 7.2% if the same sample were tested again. So a small change between two results may be noise.
NIDDK also warns that a falsely high A1C could lead to treatment changes that cause low blood sugar. If you have anemia, kidney disease or a known variant, tell your doctor. They may lean on glucose tests or a CGM instead.
How often should A1C be checked?
A1C should be checked at least twice a year if you have diabetes and are meeting your goals, the ADA says, and every 3 months if you’re not at goal or your treatment has changed. With prediabetes, the ADA and MedlinePlus suggest testing every 1 to 2 years. The A1C test isn’t a fasting test, so you can eat and drink beforehand.
NIDDK says the A1C shouldn’t be used to diagnose type 1 diabetes or diabetes in pregnancy. For the signs that should prompt a first test, see our guide to diabetes symptoms.
What is time in range on a CGM?
Time in range is the share of the day your CGM readings sit between 70 and 180 mg/dL (3.9 to 10.0 mmol/L). The ADA says most people should aim for at least 70%, about 17 of every 24 hours. It shows the daily highs and lows an A1C hides, and it helps most if you have type 1 diabetes or use insulin. The ADA notes that A1C is still the standard test.
| CGM goal | Most adults with diabetes | Older or higher-risk adults |
|---|---|---|
| Time in range (70 to 180 mg/dL) | Over 70% | Over 50% |
| Time from 54 to 69 mg/dL | Under 4% | Under 1% |
| Time below 54 mg/dL | Under 1% | Under 1% |
Source: ADA Standards of Care 2025. A time in range of 70% lines up with an A1C of about 7%. Your CGM report may also show a glucose management indicator (GMI), an A1C estimate worked out from your readings. The ADA says it isn’t always the same as a lab A1C.
Your next step
Find your latest A1C and look up its estimated average in the chart. Then compare it with your typical meter readings. If they’re far apart, note any anemia, kidney problems or recent blood loss and take that list to your doctor. Day to day, your food choices feed into both numbers. Our high-fiber foods list and the free 7-day meal plan are easy places to start. If you have diabetes, check any new eating plan with your care team first.
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Quick questions
Is A1C a fasting test?
A1C isn’t a fasting test. You can eat and drink normally before it, because it reflects your average blood sugar over about 2 to 3 months, the American Diabetes Association says. If your doctor also orders a fasting glucose test at the same visit, you’ll still need to fast for that one.
What is a good time in range?
A good time in range for most adults with diabetes is over 70%, meaning readings between 70 and 180 mg/dL for about 17 of every 24 hours, the ADA says. For older or higher-risk adults the goal is over 50%. Time below 70 mg/dL should stay under 4%, and below 54 under 1%.
Can A1C be falsely elevated?
A1C can be falsely elevated. NIDDK says iron-deficiency anemia can make it read high. Kidney failure, liver disease, recent blood loss, transfusions and some hemoglobin variants can also throw it off. If your A1C doesn’t match your meter or CGM readings, ask your doctor whether another test would suit you better.
What is the correlation between A1C and blood sugar?
A1C and average blood sugar are closely linked. In the ADAG study the correlation was 0.92, and the formula is average glucose (mg/dL) = 28.7 × A1C − 46.7. Each 1% rise in A1C means an average about 29 mg/dL higher. An A1C of 7% equals about 154 mg/dL.
How often should A1C be checked?
If you have diabetes and are meeting your goals, A1C should be checked at least twice a year, the American Diabetes Association says, and every 3 months if you’re not at goal or your treatment has changed. With prediabetes, the ADA and MedlinePlus suggest testing every 1 to 2 years.
This article is general information, not medical advice. A1C and blood sugar goals differ from person to person, and only your doctor can diagnose diabetes or set your targets. If your A1C and meter readings don’t match, talk to your care team before changing anything. Don’t change any diabetes medicine on your own.
Sources
- American Diabetes Association. Understanding A1C
- American Diabetes Association. 6. Glycemic Goals and Hypoglycemia: Standards of Care in Diabetes, 2025
- American Diabetes Association. CGM and Time in Range
- American Diabetes Association. Diagnosis
- Nathan DM, et al. Translating the A1C assay into estimated average glucose values. Diabetes Care, 2008
- NIDDK. The A1C Test and Diabetes
- NIDDK. The A1C Test and Race/Ethnicity
- CDC. Diabetes Testing
- MedlinePlus. Hemoglobin A1C (HbA1c) Test
- Cleveland Clinic. A1C