Direct Answer
Net Promoter Score (NPS) is a customer-loyalty metric calculated by asking 'How likely are you to recommend us to a friend?' on a 0–10 scale. Subtract the percentage of detractors (0–6) from the percentage of promoters (9–10). Service-business NPS averages 30–50; world-class companies hit 70+.
Voice answer (≤30 words)
“Net Promoter Score is a loyalty metric. Subtract the percent of detractors from the percent of promoters. Healthy NPS is thirty to fifty.”
Survey at a stable point — typically 30 days post-job. Don't survey at the moment of the most-positive emotion.
Always ask 'why?' as a follow-up — the qualitative comments are where the operational wins live.