NPS vs CES: when to use each one
NPS and CES often show up together in lists of "customer experience metrics", but they measure different things and answer different questions. Confusing them leads to picking the wrong metric for the wrong moment, and ending up with a number that doesn't help you decide anything.
What each one measures
NPS measures loyalty toward the whole brand: "How likely are you to recommend us?", on a 0-to-10 scale. It's a snapshot of the overall relationship, accumulated across every interaction the person has had with the company. CES measures the effort of a specific interaction: "How easy was it to resolve your issue today?", focused on a single moment, not the whole relationship.
When to use NPS
NPS works best as a periodic tracking metric (quarterly or semi-annual), sent to the whole customer base without depending on something specific having just happened. It's useful for seeing loyalty trends over time and detecting whether something shifted in the overall perception of the brand.
When to use CES
CES works best right after an interaction with measurable effort: closing a support ticket, completing a checkout, finishing an onboarding flow. Sending it immediately after the interaction (transactional, not periodic) is what makes it useful — asking about the effort of something that happened a month ago gives an unreliable answer.
An example where both are used without stepping on each other
A software company might send NPS every quarter to its whole base to monitor overall loyalty, and CES automatically after every closed support ticket to monitor how easy that specific issue was to resolve. The two numbers coexist fine because they measure different questions — in fact, a sustained high CES over time often shows up later as a higher NPS.
The question you shouldn't be asking
"Which one is better?" has no answer, because they're not competing for the same job. The useful question is "what do I need to know right now: how the overall relationship is going, or how hard was the thing that just happened?" — the answer to that tells you which metric applies.