Free Diabetes TrackerWhat HbA1c measures
HbA1c is a blood test that shows your average blood sugar over the past 2 to 3 months. It measures how much glucose (sugar) has become stuck to the haemoglobin in your red blood cells, and because those cells live for a few months the result reflects that whole period.
That makes it different from a day-to-day finger-prick reading. A meter tells you your blood sugar at one moment; HbA1c tells you the overall trend. Diabetes UK and NICE use it both to help diagnose diabetes and to track how well things are being managed over time.
The units: mmol/mol and %
In the UK HbA1c is reported in mmol/mol – the IFCC unit agreed internationally by the WHO. An older unit, a percentage (%), is still sometimes used, so you may see both quoted side by side.
What the bands mean
These are the bands used to assess diabetes risk. A diagnosis is made by a clinician reviewing your results, not by a single home reading.
| HbA1c (mmol/mol) | Older unit (%) | What it means |
|---|---|---|
| Below 42 | Below 6.0 | Non-diabetic range |
| 42 to 47 | 6.0 to 6.4 | Prediabetes – high risk of type 2 |
| 48 or above | 6.5 or above | Diabetes range |
Your management target
Once you have diabetes, HbA1c becomes a goal to aim for rather than a diagnosis. NICE supports many adults with type 1 or type 2 to aim for 48 mmol/mol (6.5%) or lower. People taking medicines that can cause hypos (low blood sugar), or taking more than one medicine, may be given a target of 53 mmol/mol (7.0%) instead.
| Situation | Typical target |
|---|---|
| Managed by diet, or medicines that don't cause hypos | 48 mmol/mol (6.5%) or lower |
| On a medicine that can cause hypos, or on more than one medicine | 53 mmol/mol (7.0%) |
Targets are individual – older or frail people may be given a higher, safer target to avoid the risk of hypos. Agree yours with your diabetes team.
How often it is checked
HbA1c is usually checked every 3 to 6 months while things are changing – for example after a new medicine or a change in dose – and at least once a year when things are stable.
HbA1c and your daily readings
Because HbA1c is an average, a lot of highs and lows can still average out to a “good” number. That is why your day-to-day pattern and your time-in-range matter too, not just the HbA1c on its own. Two people with the same HbA1c can have very different days.
Logging your finger-prick readings fills in that detail. You can start logging free and read more about understanding your numbers to see how the two fit together.
No maths needed from you
There is a standard formula to convert between mmol/mol and the older percentage, but you do not need to work it out – your results will show both units. If only one is given, your diabetes team can tell you the other.
HbA1c in pregnancy
HbA1c is not used to monitor blood sugar during pregnancy. Finger-prick targets are used instead, because blood sugar needs watching far more closely and over a much shorter timescale than a 3-month average can show.
Checked against NHS and NICE guidance on . See all official sources.