What is the cost of quality?
The cost of quality (COQ) puts quality in the language of management: money. It adds up everything spent to prevent and find defects, and everything lost because defects happened. The idea goes back to Joseph Juran and Armand Feigenbaum in the 1950s, and the prevention-appraisal-failure (PAF) model is still the most widely used way to structure it.
The PAF model
| Category | Group | Examples |
|---|---|---|
| Prevention | Cost of good quality | Quality planning, training, supplier development, FMEA, process validation |
| Appraisal | Cost of good quality | Incoming, in-process and final inspection, lab testing, calibration, audits |
| Internal failure | Cost of poor quality | Scrap, rework, re-inspection, deviation investigations, downtime |
| External failure | Cost of poor quality | Complaints, returns, warranty, field corrections, recalls |
Cost of quality example
A medical device plant with $48 million revenue adds up its cost of quality for FY 2026: $3.48 million, 7.3% of revenue, down from $4.24 million (9.4%) in FY 2025. The plant spent $95,000 more on prevention, led by its supplier quality programme, and $30,000 less on appraisal, while failure costs fell by $825,000. The biggest reductions were field corrections (−$290,000), scrap (−$140,000) and rework (−$110,000). Failures are still 56% of the cost of quality, down from 65%, and scrap remains the largest single item at $640,000, so the next prevention projects target scrap.
Tips
- Start with what you have and estimate the rest; refine the numbers over time.
- Use the same rules every period so the trend is real.
- Report it as a % of revenue to remove the effect of volume.
- Estimate the hidden failure costs as well with the cost of poor quality calculator, and attack the largest items with a Pareto chart.
How to use this Cost of Quality tool
- Set the scope. Enter the organisation, currency, the period and the revenue, and optionally a prior period to compare.
- List the cost items. In each of the four category tables, add the cost items and their amounts for this period and the prior one.
- Read the totals. The stacked bars compare the four categories between periods and show the cost of quality as a % of revenue.
- Find the big items. The ranked list shows the largest cost items, with a tick for their prior-period value.
- Shift the balance. Plan prevention activities that remove the biggest failure costs.
- Export. Export the chart and tables to PDF, PNG or Excel for the management review.
Frequently asked questions
What is the cost of quality (COQ)?
The cost of quality is the total cost of making sure products and services meet requirements, plus the cost of failing to. In the classic PAF model it has four categories: prevention, appraisal, internal failure and external failure. Prevention and appraisal are the cost of good quality; internal and external failure are the cost of poor quality.
What are the four categories of the cost of quality?
Prevention costs stop defects from happening (quality planning, training, supplier development, design reviews, process validation). Appraisal costs find defects (inspection, testing, audits, calibration). Internal failure costs arise from defects found before delivery (scrap, rework, re-inspection, investigations, downtime). External failure costs arise after delivery (complaints, returns, warranty, field actions, lost customers).
What is a typical cost of quality?
Published estimates vary widely; figures of 5% to 30% of sales are often quoted, with mature quality systems at the low end. More useful than the total is its mix and trend: failure costs should fall as prevention grows.
Why invest in prevention?
Defects get more expensive the later they are found: a problem prevented in design costs little, the same problem found at final inspection costs more, and found by the customer costs most. Shifting spend from failure to prevention usually lowers the total cost of quality, which is what the period comparison in this tool shows.
Where do I find the cost data?
Finance can provide scrap, warranty and returns. Many costs need estimating from hours and rates: inspection and testing time, investigation time, rework labour. Start with rough estimates for the biggest items; precision matters less than consistency from period to period.
What is the difference between COQ and COPQ?
The cost of quality includes all four categories. The cost of poor quality covers only the failure costs, and often includes hidden costs such as lost capacity, expediting and lost sales. Use the cost of poor quality tool to estimate those.