What is the difference between A1C and GMI?

A1C is measured from a blood sample and reflects longer-term glucose exposure. GMI is an A1C-like estimate calculated from your CGM average glucose. They describe related but different things and may not match exactly.

Can GMI replace a lab A1C test?

No. GMI is an estimate based on CGM average glucose and is meant to complement, not replace, a laboratory-measured A1C. Both can be reviewed together with your healthcare provider.

Why is my GMI different from my A1C?

A1C and GMI can differ because of individual glucose variability, red blood cell factors, the time periods each measurement covers, and other health conditions. A difference does not mean either number is wrong.

Can I estimate A1C from average glucose?

A1C is not calculated directly from blood glucose. It is measured from glycated hemoglobin in your blood. Average glucose may help estimate your A1C, but it cannot determine your actual A1C. Use this estimate as a reference point, not as a replacement for checking your A1C.

Can one fasting glucose reading predict my A1C?

No. A single fasting glucose reading cannot reliably estimate A1C. A1C reflects glucose exposure over a longer period, so an average of many readings works better.

What does Time in Range mean?

Time in Range is the percentage of time your glucose stayed within a target range, commonly 70-180 mg/dL. It describes how much of your day was spent in range.

What is the difference between mmol/L and mmol/mol?

A1C can be reported as % or as IFCC mmol/mol. Blood glucose and estimated average glucose are reported as mg/dL or mmol/L. These units are related through conversion formulas, but mmol/L and mmol/mol are not the same unit. For example, an A1C of 7.0% is about 53 mmol/mol in IFCC A1C units, and it corresponds to an estimated average glucose of about 154 mg/dL or 8.6 mmol/L.

What A1C level is considered prediabetes?

As a general educational reference, an A1C from 5.7% to 6.4% is often described as the prediabetes range. Diagnosis should be made by a qualified healthcare professional.

What A1C level is considered diabetes?

As a general educational reference, an A1C of 6.5% or higher is often described as the diabetes range. Diagnosis should be made by a qualified healthcare professional.

A1C Calculator & Conversion Chart: A1C to eAG, GMI, mmol/mol

Q: Does Time in Range convert to A1C?

No. Time in Range does not directly convert to A1C. Two people with the same Time in Range can have different A1C results because of glucose variability and other factors.

A1C conversion chart: A1C %, eAG, and IFCC mmol/mol

This chart converts an A1C result into estimated average glucose (eAG) in mg/dL and mmol/L, and into IFCC A1C units (mmol/mol). Use it to read a result that was reported in units you are not used to. The conversions come from the published NGSP and ADAG equations listed under Formulas used on this page.

eAG is an estimate of your average glucose over roughly the past two to three months. It is not the same thing as a single glucose meter reading, and a single reading will often fall above or below it.

A1C to estimated average glucose and IFCC units, 4.0% to 14.0%
A1C (%)	eAG (mg/dL)	eAG (mmol/L)	IFCC (mmol/mol)	General educational category
4.0%	68	3.8	20	Normal range
4.1%	71	3.9	21	Normal range
4.2%	74	4.1	22	Normal range
4.3%	77	4.3	23	Normal range
4.4%	80	4.4	25	Normal range
4.5%	82	4.6	26	Normal range
4.6%	85	4.7	27	Normal range
4.7%	88	4.9	28	Normal range
4.8%	91	5.1	29	Normal range
4.9%	94	5.2	30	Normal range
5.0%	97	5.4	31	Normal range
5.1%	100	5.5	32	Normal range
5.2%	103	5.7	33	Normal range
5.3%	105	5.9	34	Normal range
5.4%	108	6.0	36	Normal range
5.5%	111	6.2	37	Normal range
5.6%	114	6.3	38	Normal range
5.7%	117	6.5	39	Prediabetes range
5.8%	120	6.6	40	Prediabetes range
5.9%	123	6.8	41	Prediabetes range
6.0%	125	7.0	42	Prediabetes range
6.1%	128	7.1	43	Prediabetes range
6.2%	131	7.3	44	Prediabetes range
6.3%	134	7.4	45	Prediabetes range
6.4%	137	7.6	46	Prediabetes range
6.5%	140	7.8	48	Diabetes range
6.6%	143	7.9	49	Diabetes range
6.7%	146	8.1	50	Diabetes range
6.8%	148	8.2	51	Diabetes range
6.9%	151	8.4	52	Diabetes range
7.0%	154	8.6	53	Diabetes range
7.1%	157	8.7	54	Diabetes range
7.2%	160	8.9	55	Diabetes range
7.3%	163	9.0	56	Diabetes range
7.4%	166	9.2	57	Diabetes range
7.5%	169	9.4	58	Diabetes range
7.6%	171	9.5	60	Diabetes range
7.7%	174	9.7	61	Diabetes range
7.8%	177	9.8	62	Diabetes range
7.9%	180	10.0	63	Diabetes range
8.0%	183	10.2	64	Diabetes range
8.1%	186	10.3	65	Diabetes range
8.2%	189	10.5	66	Diabetes range
8.3%	192	10.6	67	Diabetes range
8.4%	194	10.8	68	Diabetes range
8.5%	197	10.9	69	Diabetes range
8.6%	200	11.1	70	Diabetes range
8.7%	203	11.3	72	Diabetes range
8.8%	206	11.4	73	Diabetes range
8.9%	209	11.6	74	Diabetes range
9.0%	212	11.7	75	Diabetes range
9.1%	214	11.9	76	Diabetes range
9.2%	217	12.1	77	Diabetes range
9.3%	220	12.2	78	Diabetes range
9.4%	223	12.4	79	Diabetes range
9.5%	226	12.5	80	Diabetes range
9.6%	229	12.7	81	Diabetes range
9.7%	232	12.9	83	Diabetes range
9.8%	235	13.0	84	Diabetes range
9.9%	237	13.2	85	Diabetes range
10.0%	240	13.3	86	Diabetes range
10.1%	243	13.5	87	Diabetes range
10.2%	246	13.7	88	Diabetes range
10.3%	249	13.8	89	Diabetes range
10.4%	252	14.0	90	Diabetes range
10.5%	255	14.1	91	Diabetes range
10.6%	258	14.3	92	Diabetes range
10.7%	260	14.5	93	Diabetes range
10.8%	263	14.6	95	Diabetes range
10.9%	266	14.8	96	Diabetes range
11.0%	269	14.9	97	Diabetes range
11.1%	272	15.1	98	Diabetes range
11.2%	275	15.2	99	Diabetes range
11.3%	278	15.4	100	Diabetes range
11.4%	280	15.6	101	Diabetes range
11.5%	283	15.7	102	Diabetes range
11.6%	286	15.9	103	Diabetes range
11.7%	289	16.0	104	Diabetes range
11.8%	292	16.2	105	Diabetes range
11.9%	295	16.4	107	Diabetes range
12.0%	298	16.5	108	Diabetes range
12.1%	301	16.7	109	Diabetes range
12.2%	303	16.8	110	Diabetes range
12.3%	306	17.0	111	Diabetes range
12.4%	309	17.2	112	Diabetes range
12.5%	312	17.3	113	Diabetes range
12.6%	315	17.5	114	Diabetes range
12.7%	318	17.6	115	Diabetes range
12.8%	321	17.8	116	Diabetes range
12.9%	324	18.0	117	Diabetes range
13.0%	326	18.1	119	Diabetes range
13.1%	329	18.3	120	Diabetes range
13.2%	332	18.4	121	Diabetes range
13.3%	335	18.6	122	Diabetes range
13.4%	338	18.8	123	Diabetes range
13.5%	341	18.9	124	Diabetes range
13.6%	344	19.1	125	Diabetes range
13.7%	346	19.2	126	Diabetes range
13.8%	349	19.4	127	Diabetes range
13.9%	352	19.5	128	Diabetes range
14.0%	355	19.7	130	Diabetes range

Values are rounded. The category column is a general educational reference only and is not a diagnosis.

What is A1C?

A1C, also written HbA1c or glycated hemoglobin, is a blood test that reflects how much glucose has attached to the hemoglobin in your red blood cells. Because red blood cells circulate for about three months, A1C summarizes glucose exposure over that period rather than at one moment. It is reported as a percentage in the United States, and as IFCC mmol/mol in many other countries.

A1C is not calculated from a blood glucose reading. It is measured from a blood sample. Average glucose can be used to estimate an A1C, which is what the calculator above does, but an estimate is not a measured result.

For a longer introduction, see What is A1C and what hemoglobin A1C measures.

Understanding your A1C result

The following ranges are widely used as general educational references for adults who are not pregnant. Your own target may be different, and only a qualified healthcare professional can make a diagnosis or set a treatment goal.

General educational reference ranges for adults
A1C	eAG (mg/dL)	Commonly described as
Below 5.7%	Below 117	Normal range
5.7% to 6.4%	117 to 137	Prediabetes range
6.5% or higher	140 or higher	Diabetes range

Several conditions can make an A1C result higher or lower than your actual glucose exposure, including anemia, kidney disease, liver disease, hemoglobin variants, recent blood loss or transfusion, and pregnancy. If your A1C and your day-to-day glucose readings disagree, that is worth discussing with your provider rather than resolving on your own.

Self-monitoring blood glucose vs. A1C

A1C and daily glucose checks answer different questions, and neither one replaces the other.

A1C tells you the average. One number covers about three months. It is useful for seeing long-term direction, and it is the measure most treatment goals are written around.
Self-monitoring tells you the pattern. Fingerstick readings or a CGM show when glucose rises and falls, how meals and activity affect you, and whether you are having lows. None of that is visible in an A1C.

This is why two people with the same A1C can have very different days. An A1C of 7.0% can come from steady glucose near 154 mg/dL, or from swings between hypoglycemia and high post-meal peaks that happen to average out. The average looks identical; the experience and the risks do not.

The practical takeaway is that A1C is a checkpoint, not a monitor. Between A1C tests, self-monitoring is what shows whether anything needs to change, and your provider is the person to review both with. Our overview of CGM and A1C in diabetes monitoring goes into how the two fit together.

GMI and Time in Range: what CGM adds

GMI (Glucose Management Indicator) is an A1C-like estimate calculated from CGM average glucose. It is reported as a percentage, which makes it easy to confuse with a lab A1C, but the two are measured from different things and often differ by a few tenths of a percent. A gap between them does not mean either value is wrong.

Time in Range (TIR) is the share of time your glucose stayed inside a target range, commonly 70 to 180 mg/dL. TIR does not convert to A1C. Two people with the same Time in Range can have different A1C results, because TIR says nothing about how far outside the range the remaining time went.

The calculator above estimates GMI from CGM average glucose and puts a Time in Range percentage into context, including how many hours per day it corresponds to.

How A1C is measured or estimated

Laboratory test. A blood sample is analyzed by a certified laboratory. This is the reference method that treatment decisions are normally based on.
Point-of-care testing. Analyzers used in a clinic or pharmacy give a result during the visit from a small blood sample. Orange Biomed develops rapid point-of-care A1C testing for this setting.
Home test kits. Consumer kits are available; accuracy varies by product, so read what the manufacturer reports and confirm important results with your provider. See our overview of A1C testing options.
CGM-derived GMI. Calculated from CGM data. An estimate, not a measured A1C.
Calculators like this one. Estimated from average glucose using a published equation. Useful as a reference point, never as a test result.

How often is A1C checked?

A common pattern described in general diabetes education is testing at least twice a year for people who are meeting their treatment goals with stable glucose, and about every three months for people whose treatment has changed or who are not yet at goal. People without diabetes may be screened far less often, or not at all, depending on risk factors.

These are general references, not a schedule for you. How often you should be tested is a decision for your healthcare provider, based on your situation.

Formulas used on this page

eAG (mg/dL) = 28.7 × A1C% − 46.7
eAG (mmol/L) = eAG (mg/dL) ÷ 18.0182
IFCC (mmol/mol) = 10.93 × A1C% − 23.50
A1C% = 0.09148 × IFCC (mmol/mol) + 2.152
GMI (%) = 3.31 + 0.02392 × CGM mean glucose (mg/dL)

The eAG equation comes from the ADAG study and is the one used by NGSP and the ADA Professional eAG/A1C calculator. The A1C and IFCC equations are the NGSP/IFCC master equations. The GMI equation comes from the 2018 Diabetes Care paper that defined the term.

Sources

Important

This page is an educational tool. It is not a medical device, it does not diagnose or treat any condition, and the numbers it produces are estimates rather than test results.

Use this information to become more familiar with the relationship between average glucose levels and A1C — never as a basis for changing your diabetes management. Do not start, stop, or adjust any medication, insulin dose, diet, or monitoring routine because of a number on this page. Always discuss your results and your personal targets with a qualified healthcare provider.

If you have symptoms of severe hypoglycemia or hyperglycemia, contact your healthcare provider or emergency services rather than a calculator.

A1C Calculator and Conversion Chart