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Saturation is judged by the new information rate: new themes from recent interviews as a share of all themes identified. One new theme from the last three out of 32 total is 3.1%, below the 5% threshold Guest and colleagues propose, so saturation is likely reached. Most homogeneous samples saturate between twelve and twenty interviews.
New information rate
rate = new themes in the recent base / total themes x 100
Threshold
5% or below is commonly taken as evidence of saturation
Twelve to twenty for a homogeneous sample on a focused question. Heterogeneous samples or broad questions can need fifty or more.
It is the convention but is criticised as unfalsifiable. Reporting the run of interviews with no new themes is more transparent than simply asserting saturation.