Persistent absence threshold is 10%
If a pupil's overall absence rate is 10% or higher of their possible sessions, they're classified as a persistent absentee. A 'session' is 1 morning or afternoon in school.
This is based on their individual absence level, not by comparison to a national threshold.
The calculation for this is:
[A pupil’s individual overall absence divided by a pupil’s individual possible sessions] multiplied by 100. If this is greater than or equal to 10, the pupil is classified as persistently absent.
You can read more about this calculation in the DfE's guidance on pupil absence statistics, paragraph 3.2.2.