A1C Calculator
Convert between A1C percentage and estimated average glucose (eAG). A1C reflects average blood sugar over the past 2-3 months.
⚠️ For educational use. Consult your doctor for diabetes management decisions. This calculator does not diagnose or treat any condition.
Reviewed & updated for 2026 · How we calculate
A1C to glucose reference
| A1C | eAG (mg/dL) | eAG (mmol/L) | Status |
|---|---|---|---|
| 5.0% | 97 | 5.4 | Normal |
| 5.7% | 117 | 6.5 | Prediabetes (start) |
| 6.0% | 126 | 7.0 | Prediabetes |
| 6.5% | 140 | 7.8 | Diabetes (start) |
| 7.0% | 154 | 8.6 | Most diabetes target |
| 8.0% | 183 | 10.2 | Action needed |
| 9.0% | 212 | 11.8 | Poor control |
| 10.0% | 240 | 13.4 | Very poor control |
What A1C is actually measuring
Hemoglobin in red blood cells binds with glucose in the bloodstream, irreversibly. The more glucose is present over time, the higher the percentage of hemoglobin molecules that get "glycated." A1C measures that percentage. Because red blood cells live about 120 days on average, A1C gives a weighted average of blood sugar over the past 2-3 months, with more recent weeks weighted more heavily (because newer cells outnumber older ones).
This is a fundamentally different measurement than a finger-stick test (which captures one moment) or a fasting glucose test (which captures one fasted moment). A1C cannot be cheated by abstaining from carbs for a few days before the test, the glycated hemoglobin from a month ago is already locked in. That makes it the most honest signal of long-term diabetes control available without a continuous monitor.
The ADAG formula (28.7 × A1C − 46.7) used to convert A1C to estimated average glucose was developed from the ADAG study (Diabetes Care, 2008) using continuous glucose monitoring of 507 participants. The relationship is approximately linear in the 5-12% A1C range. Below 5% the formula slightly underestimates; above 14% it slightly overestimates.
A1C targets are personalized, not one-size-fits-all
The ADA's general target for adults with diabetes is below 7.0%, but the 2025 ADA Standards of Medical Care emphasize that target should be individualized. A young, healthy person newly diagnosed might aim for below 6.5% to maximize the chance of preventing long-term complications. An 85-year-old with heart disease and a history of hypoglycemia might safely target 8.0%, because aggressive lowering increases the risk of dangerous low blood sugar that outweighs the benefit of tight control.
Pregnancy is the strictest category: targets often below 6.0% to reduce risk of birth defects and large-for-gestational-age babies. Insulin requirements during pregnancy can change weekly. Conversely, frail older adults with limited life expectancy gain little from tight control and a lot from avoiding hypoglycemia.
Each 1% reduction in A1C reduces microvascular complication risk (retinopathy, nephropathy, neuropathy) by roughly 25-30% based on UKPDS and DCCT trial data. The bigger the starting A1C, the bigger the absolute benefit from lowering it. Going from 10% to 9% prevents more complications per year of effort than going from 7% to 6%.
When A1C lies, and what to use instead
- Hemoglobinopathies: Sickle cell trait, thalassemia, and certain hemoglobin variants can produce falsely high or low A1C. Use fructosamine or CGM data.
- Recent blood loss or transfusion: A transfusion replaces glycated hemoglobin with fresh, unglycated hemoglobin, A1C drops artificially. Wait 3 months for accurate testing.
- Iron-deficiency anemia: Can elevate A1C by 1-2% above true average. Treating the iron deficiency fixes the reading.
- Chronic kidney disease: Both shortens red cell lifespan (lowering A1C) and causes carbamylation (raising A1C). Net effect is unpredictable. CGM is preferred at advanced kidney disease stages.
- Pregnancy: Red cell turnover increases, lowering A1C by 0.5% on average. The pregnancy A1C targets (below 6%) account for this.
FAQs
What is A1C?
A1C (also called HbA1c or glycated hemoglobin) measures your average blood sugar over the past 2-3 months. It's expressed as a percentage representing the proportion of hemoglobin molecules that have glucose attached. Lab test, no fasting required.
What's a normal A1C?
Normal (no diabetes): under 5.7%. Prediabetes: 5.7%-6.4%. Diabetes: 6.5% or higher. Target for most people with diabetes: under 7.0%. Stricter target for younger, healthier patients: under 6.5%. Looser target for elderly or complex cases: under 8.0%.
How is A1C converted to average blood sugar?
Formula: eAG (mg/dL) = 28.7 × A1C − 46.7. Example: A1C of 7.0 → 28.7 × 7.0 − 46.7 = 154 mg/dL average. eAG (mmol/L) = (eAG mg/dL + 46.7) / 18.05, or 1.5944 × A1C − 2.594 directly.
How often should I test A1C?
If you have diabetes and are stable: every 6 months. If treatment is changing or you're not at target: every 3 months. Prediabetes monitoring: annually. After meeting glycemic targets: typically twice yearly.
Can A1C be wrong?
Some conditions affect A1C accuracy: anemia (false LOW or HIGH depending on type), recent blood transfusion (false low), kidney disease, hemoglobin variants, pregnancy (use different ranges). If A1C and home glucose readings strongly disagree, fructosamine or continuous glucose monitor (CGM) data may be more accurate.