How do you convert blood sugar to A1C?

Use the reverse ADAG formula: A1C (%) = (eAG + 46.7) ÷ 28.7. If the value is in mmol/L, multiply by 18.0182 first to get mg/dL. For example, 154 mg/dL gives (154 + 46.7) ÷ 28.7 = 7.0%. This calculator applies both steps automatically and shows the converted unit alongside the A1C result.

What blood sugar level equals an A1C of 7.0%?

An average glucose of 154 mg/dL (8.6 mmol/L) corresponds to an estimated A1C of 7.0%. This is the ADA target for most non-pregnant adults with diabetes. Entering 154 into this calculator returns 7.0%. To go in the reverse direction, use our A1C to Blood Sugar Calculator.

What average glucose should I aim for to reach an A1C of 6.5%?

To reach an A1C of 6.5%, the ADAG formula gives: eAG = (28.7 × 6.5) − 46.7 = 140 mg/dL (7.8 mmol/L). If your current CGM average is 175 mg/dL, bringing it to 140 mg/dL would move your estimated A1C from approximately 7.7% to 6.5%. A reduction of about 35 mg/dL in sustained average glucose corresponds to roughly a 1.2% drop in A1C.

Does time-in-range (TIR) affect this estimate?

Not directly. This calculator uses only the average glucose, not the distribution of highs and lows. Two people with the same average glucose of 154 mg/dL can have very different glucose profiles: one spending most of the day between 120 and 180 mg/dL (good TIR), another swinging from 60 to 280 mg/dL. Both produce the same estimated A1C. TIR is a separate and complementary metric that A1C alone does not capture.

How long does it take to see a change in A1C after improving my glucose average?

A1C reflects approximately 90 days of glucose history, so changes take time to appear in a lab result. However, the most recent 30 days contribute more to A1C than the earlier 60 days because newer red blood cells are more abundant. A meaningful reduction in average glucose sustained for 4 to 6 weeks will typically move the next A1C reading by 0.3 to 0.5%, with the full effect visible after a complete 90-day cycle.

Blood Sugar to A1C Calculator | Average Glucose to HbA1c

Q: Can I use my CGM average to predict my next A1C?

Yes, with one important caveat: your CGM reports a 7-day, 14-day, or 30-day average, while A1C reflects approximately 90 days. If you enter a 14-day CGM average, the estimate will weight recent glucose more heavily than your upcoming lab result will. For the closest prediction, use a 90-day CGM average. Most modern devices (Libre 3, Dexcom G7) can display a 90-day average in settings.

The Blood Sugar to A1C Calculator converts a sustained average blood glucose value in milligrams per decilitre (mg/dL) or millimoles per litre (mmol/L) into an estimated HbA1c percentage. It is designed for people who track glucose with a continuous glucose monitor (CGM) or a home logbook and want to estimate what their next lab A1C is likely to show. The converted unit appears alongside the result so you can see both without switching inputs.

About this estimate: This calculator applies the reverse of the ADAG formula. The result is most accurate when the glucose value entered represents a true 90-day average, matching the window that an A1C lab test reflects. A 7-day or 14-day CGM average will produce an estimate weighted toward recent trends. For a confirmed A1C, a blood test is required.

Unit

Average Blood Glucose (mg/dL) Use a sustained average, not a single reading. A 90-day CGM average gives the closest match to a lab A1C.

Estimated A1C

Estimated HbA1c

Equivalent in mmol/L

A1C Category

Formula applied:

About This Calculator

What it calculates: Estimated HbA1c percentage from a sustained average blood glucose in mg/dL or mmol/L.
Inputs required: Average blood glucose value and unit (mg/dL or mmol/L). Best input is a 90-day CGM average.
Outputs: Estimated A1C %, converted unit value, and A1C category (Normal / Prediabetes / Diabetes ranges)
Formula: Reverse ADAG: A1C (%) = (eAG mg/dL + 46.7) ÷ 28.7; mmol/L inputs multiplied by 18.0182 first
Assumptions: Based on the 2008 ADAG study. Most accurate when the input represents a 90-day sustained average. Not suitable for single readings or 7-day windows.
Last updated: March 2026

How to Use This Calculator

Select the unit your device displays. Meters and CGMs in India and the United States use mg/dL. Devices sold in the UK, Australia, and most of Europe use mmol/L. The toggle updates the input and shows the converted unit in the result automatically.
Enter your average glucose. Open your CGM app and find the average glucose for the longest available window — ideally 90 days. On FreeStyle Libre, this appears in the AGP report. On Dexcom Clarity, check the Trends or Summary section. For a paper logbook, total your readings and divide by the count.
Click Calculate A1C. Results appear immediately: estimated HbA1c, the converted unit value, and the ADA category.
Compare with your upcoming lab result. If the estimate and lab A1C diverge by more than 0.5%, review the factors below that can cause a gap.

How CGM Averages Map to A1C

A continuous glucose monitor measures glucose in the interstitial fluid every 1 to 5 minutes. Over a day, it generates hundreds of readings. The device averages these into a single number — the mean glucose — displayed in the app summary. The ADAG study established that this kind of sustained mean glucose correlates closely with HbA1c, with a correlation coefficient of 0.92 across 507 participants in four countries.

This calculator applies the reverse of that relationship. Given a mean glucose, it returns the A1C that the ADAG model predicts. The result is an estimate, not a lab measurement, but it is the same mathematical basis that the American Diabetes Association uses when it reports eAG alongside A1C on lab reports.

Why CGM Window Length Matters

HbA1c reflects red blood cells that have been circulating for up to 120 days, though the most recent 30 days contribute more because newer cells are more abundant. Research published in Diabetes Care suggests that roughly 50% of A1C is determined by the most recent 30 days, 25% by the preceding month, and 25% by the two months before that.

This means a 14-day CGM average will overweight very recent glucose and underrepresent trends from 6 to 10 weeks ago. If you made dietary changes two weeks ago and your recent CGM average improved sharply, this calculator will produce a more optimistic A1C estimate than the lab will return — because the lab is still accounting for the higher glucose from 6 weeks prior. A 90-day CGM average distributes the weighting more evenly and gives a closer prediction.

Why Your Estimated A1C May Not Match the Lab

Even with a 90-day average, a gap between the estimate and the lab result is common for four reasons. First, CGMs measure interstitial glucose, which lags behind blood glucose by 5 to 15 minutes. Post-meal spikes in blood glucose are often partially smoothed out in the CGM record. Second, CGM sensors apply proprietary calibration algorithms that vary between manufacturers. A Libre 3 average and a Dexcom G7 average for the same person on the same days can differ by 5 to 10 mg/dL. Third, individual variation in red blood cell lifespan means some people consistently run a higher or lower A1C than the formula predicts. Fourth, conditions such as iron deficiency anaemia and haemoglobin variants affect the lab A1C value without affecting actual glucose. For a broader picture of metabolic health, our BMI Calculator and Body Fat Calculator provide complementary screening data.

Time-in-Range vs A1C

Average glucose and A1C capture one dimension of glycaemic control: how high the mean is. Time-in-range (TIR) captures a different dimension: what proportion of the day glucose stays within a target band, typically 70 to 180 mg/dL. Two people with an identical CGM average of 154 mg/dL, and therefore the same estimated A1C of 7.0%, can have very different TIR scores. One might spend 85% of the day in range with minimal spikes; the other might spend 50% in range but offset by deeper lows and higher peaks that average out to the same mean. A1C cannot distinguish between these profiles. TIR and A1C are complementary, not interchangeable.

The Reverse ADAG Formula

The forward ADAG formula converts A1C to estimated average glucose: eAG (mg/dL) = 28.7 × A1C − 46.7. Rearranging algebraically for A1C gives:

A1C (%) = (eAG + 46.7) ÷ 28.7

Where:

eAG = average blood glucose in mg/dL
46.7 and 28.7 = regression coefficients derived from the 2008 ADAG study dataset

For mmol/L inputs, the unit conversion is applied first:

eAG (mg/dL) = eAG (mmol/L) × 18.0182

The calculator handles both steps automatically. The formula is shown here for transparency.

Worked example: CGM average of 154 mg/dL (8.6 mmol/L)

A1C = (154 + 46.7) ÷ 28.7 = 200.7 ÷ 28.7 = 7.0%

Same value entered in mmol/L: 8.6 mmol/L

Convert: 8.6 × 18.0182 = 154.96 ≈ 155 mg/dL
A1C = (155 + 46.7) ÷ 28.7 = 7.0%

A sustained 90-day CGM average of 154 mg/dL corresponds to an estimated A1C of 7.0%, the ADA target for most adults with diabetes. To work in the reverse direction, use our A1C to Blood Sugar Calculator.

CGM Average to A1C Reference Table

The table below shows how common CGM average values map to estimated A1C percentages using the ADAG formula. Use it to quickly locate where your device average sits without entering individual values.

CGM Avg (mg/dL)	CGM Avg (mmol/L)	Est. A1C (%)	Category
100	5.6	5.1	Normal
110	6.1	5.5	Normal
117	6.5	5.7	Prediabetes threshold
130	7.2	6.2	Prediabetes
140	7.8	6.5	Diabetes threshold
154	8.6	7.0	ADA target
169	9.4	7.5	Above ADA target
183	10.2	8.0	Above ADA target
212	11.8	9.0	Well above target
240	13.3	10.0	Significantly elevated

To find what average glucose a specific A1C target requires, use our A1C to Blood Sugar Calculator in reverse. For example, to reach an A1C of 6.5%, sustaining an average glucose below 140 mg/dL (7.8 mmol/L) is the corresponding target. For lifestyle factors that influence daily glucose, our Calorie Calculator can help estimate dietary intake targets alongside medical management.

Common Mistakes When Using a CGM Average to Estimate A1C

Using a 7-day average after a good week. A strong 7-day period may reflect temporary behaviour changes — a holiday, illness recovery, or unusual activity — rather than sustained control. Entering it produces an optimistic estimate. If your typical average over the past two months was 175 mg/dL but your last 7 days averaged 140 mg/dL, the lab A1C will reflect the longer pattern.
Comparing the estimate to the wrong lab A1C. If your most recent lab A1C was drawn 6 weeks ago and your glucose has changed significantly since then, the estimate from today's CGM average will not align with that older result. The estimate reflects current patterns; the lab reflects the period ending at the draw date.
Ignoring sensor accuracy variation between brands. Different CGM brands calibrate differently. A person wearing a Libre 3 and a Dexcom G7 simultaneously may see average glucose values that differ by 5 to 15 mg/dL, producing estimated A1C values roughly 0.2 to 0.5% apart. Both sensors can be clinically acceptable, but the brand used affects what this calculator returns.
Treating this as a diagnostic result. This calculator produces a mathematical estimate based on a population formula. It cannot diagnose diabetes or prediabetes. Only a certified lab HbA1c test provides a clinically valid result for diagnosis or treatment decisions. Use this tool to prepare for and contextualise lab appointments, not to replace them.

Frequently Asked Questions

Use the reverse ADAG formula: A1C (%) = (eAG + 46.7) ÷ 28.7. If the value is in mmol/L, multiply by 18.0182 first. For example, 154 mg/dL gives (154 + 46.7) ÷ 28.7 = 7.0%. This calculator applies both steps automatically and shows the converted unit alongside the A1C result.

Yes, with one important caveat. Your CGM reports a 7-day, 14-day, or 30-day average while A1C reflects approximately 90 days. If you enter a 14-day average, the estimate will weight recent glucose more heavily than the upcoming lab result will. For the closest prediction, use a 90-day CGM average. Most modern devices such as Libre 3 and Dexcom G7 can display a 90-day average in the app settings or AGP report.

Three main reasons. First, CGM covers a shorter time window than A1C. Second, CGM measures interstitial glucose, which lags behind blood glucose by roughly 5 to 15 minutes, smoothing out some post-meal spikes. Third, CGM algorithms apply calibration adjustments that vary by sensor brand. A divergence of 0.3 to 0.5% between the CGM-estimated A1C and the lab A1C is within the normal expected range.

An average glucose of 154 mg/dL (8.6 mmol/L) corresponds to an estimated A1C of 7.0%. This is the ADA target for most non-pregnant adults with diabetes. To go in the other direction and find what glucose average a given A1C implies, use our A1C to Blood Sugar Calculator.

To reach an A1C of 6.5%, the forward ADAG formula gives: eAG = (28.7 × 6.5) − 46.7 = 140 mg/dL (7.8 mmol/L). If your current CGM average is 175 mg/dL, sustaining a reduction of 35 mg/dL over 90 days would be expected to bring your A1C from approximately 7.7% down to 6.5%. A reduction of roughly 29 mg/dL corresponds to a 1% drop in A1C.

The ADAG formula has a reported correlation of 0.92 between A1C and eAG across diverse populations. However, individual variation exists. People with conditions affecting red blood cell lifespan, such as iron deficiency anaemia, haemolytic anaemia, or sickle cell trait, may have a lab A1C that consistently reads higher or lower than this estimate predicts. Use this as an estimate for planning and context, not a lab substitute.

Not directly. This calculator uses only the average glucose, not the distribution of highs and lows. Two people with the same CGM average of 154 mg/dL will get the same estimated A1C of 7.0%, even if one spends 85% of the day in the 70 to 180 mg/dL range and the other swings between 60 and 280 mg/dL. Time-in-range and A1C are complementary metrics that measure different aspects of glycaemic control.

A1C reflects approximately 90 days of glucose history, but the most recent 30 days contribute roughly 50% of the result. A meaningful reduction in average glucose sustained for 4 to 6 weeks will typically move the next A1C reading by 0.3 to 0.5%, with the full effect visible after a complete 90-day cycle. Entering an improved CGM average into this calculator shows the A1C you are trending toward if the improvement is maintained.

Calculator Category

This tool belongs to Health Calculators. Browse similar tools for related calculations.

Results are for informational purposes only and do not constitute medical advice. Consult a qualified healthcare professional for personal guidance.

Blood Sugar to A1C Calculator