Last updated: 7 October 2026
Quick Answer: A customer satisfaction index, or CSI, is a single 0 to 100 score built by weighting several customer satisfaction ratings together. The American Customer Satisfaction Index averages three 1 to 10 questions on satisfaction, expectations and an ideal. Its national US score stood at 76.7 in the first quarter of 2026.
A customer satisfaction index is a composite score that blends several weighted satisfaction ratings into one number from 0 to 100. Companies build their own; the US has a national one.
That design keeps an index steady, and it means a falling index says something changed without saying what.
Which Survey Questions Feed a CSI?
A customer satisfaction index asks several related satisfaction questions, converts each to a 0 to 100 scale and combines them with weights. Weights come from importance ratings or a model of what best predicts loyalty.
The ACSI uses three 10-point questions, as its researchers describe in a 2023 data paper:
- Overall satisfaction with the company or brand.
- How far it fell short of or exceeded expectations.
- How close it comes to an ideal product or service.
How Is a CSI Score Calculated?
To calculate a CSI score, rescale each question's mean to 0 to 100, then take a weighted average. On a 1 to 10 scale, the customer satisfaction index formula for each question is (mean minus 1) ÷ 9 × 100. A 2000 Department of Labor letter shows one example:
| ACSI question | Mean (1 to 10) | Rescaled (0 to 100) | Weight |
|---|---|---|---|
| Overall satisfaction | 8.3 | 81.1 | 0.3804 |
| Met expectations | 7.9 | 76.7 | 0.3247 |
| Compared with ideal | 7.0 | 66.7 | 0.2949 |
| Index | 75.4 | 1.0000 |
Rows follow survey order.
What Is the ACSI and What Is the Current Score?
The ACSI, or American Customer Satisfaction Index, is a national economic indicator of US consumer satisfaction, begun in 1994 at the University of Michigan by Claes Fornell. It now surveys some 400,000 consumers a year on more than 400 companies in about 50 industries, per its researchers.
The national ACSI score was 76.7 in the first quarter of 2026, according to ACSI LLC, before a sharp second-quarter fall.
How Is a CSI Different From CSAT and NPS?
A customer satisfaction index combines several questions into one weighted score, while CSAT and NPS each rest on a single question. CSAT reports the share of satisfied customers after an interaction; NPS reports promoters minus detractors on a recommend question.
That is the customer satisfaction index meaning in practice: steadier and harder to game than one question, but less tied to one touchpoint.
Can a Company Build Its Own Customer Satisfaction Index?
Yes, a company can build its own customer satisfaction index, but it cannot call the result an ACSI score. Department of Labor guidance noted that the three core questions are public domain, while the ACSI name, weights, formula and comparisons are proprietary and need a license.
Licensing has a price. In one customer satisfaction index example, the National Institutes of Health licensed the ACSI survey for 60 websites at $18,000 each; 42 produced enough data to report.
Which Customers Never Make It Into the Index?
A satisfaction index leaves out anyone its collection method cannot reach. The ACSI moved from landline phone interviews to internet panels in 2015, and Pew Research Center puts US internet use at 96% of adults, so online panels miss the offline 4%.
WhatsApp-native interviews and AI phone interviews ask the same rating questions where customers already are. Alchemic publishes 60+ languages including Spanish and Hindi, across 14 markets including the USA and the UK.
Where Does a CSI Fall Short?
A customer satisfaction index falls short as a diagnostic, because a weighted average hides which experience moved it. A two-point drop shows on the dashboard; the broken delivery promise behind it does not. Brand equity measures have the same limit.
Deeper Brand Tracks adds 40 to 80 AI-moderated interviews to each tracker wave so the reason arrives with the score. Once it has the client's brief, Alchemic designs and tailors the discussion guide to handle these risks before fielding, rather than leaving that work to the buyer. A company that only needs an external yardstick is better served licensing ACSI benchmarks.