Ask one question, right after the ticket is solved
The standard question is “How satisfied were you with the help you received?” on a five point scale, sent when the ticket is solved. Keep it to one question and one click. Every extra field lowers the answer rate.
Put the survey inside the reply
A rating link or buttons in the reply email tend to get more answers than a separate survey email a day later. The customer is already looking at the answer, so asking then costs them no effort.
How to calculate it
CSAT is the share of answers that are a 4 or 5, out of all answers. 90 satisfied answers out of 100 is 90%. Count answers, not tickets: a ticket nobody rated is not part of the score.
Read it with its margin of error
With few answers the score moves a lot by chance alone. Forty answers can shift ten points with no real change in service. The CSAT calculator gives the range your true score probably sits in. If this week's score is inside last week's range, nothing changed.
Watch the response rate
If only 5% of customers answer, you are mostly hearing from people who felt strongly, good or bad. Track the response rate beside the score, and do not compare scores between periods with very different rates.
Read the comments, not just the number
The score tells you if something is wrong; the comment tells you what. Read every low rating once a week, tag the cause, and fix one thing. That is how the score moves.
Do not coach the answer
Agents who ask for a five, or send the survey only after happy tickets, make the score meaningless. Send it to every solved ticket and leave it alone.