Cost of Quality

Cost technique · See it on the map

Runnable here

Sorting quality spending into four buckets, to see if a project pays to prevent defects or fix them.

When to use it

When you're deciding how much to invest in preventing and catching defects, or when rework and warranty costs are climbing and you want to know whether more prevention spend would actually pay for itself. Also useful whenever quality-related costs need to be visible as a category, not buried inside general cost overruns.

When to avoid it

Don't build the four-bucket breakdown on a project too small or too short to have a meaningful quality cost signal — the categorization overhead will exceed anything it reveals. And don't treat a low failure cost as proof prevention spend is working; it might just mean nobody has found the defects yet.

Steps

1. Define the four categories for this project in concrete terms: what counts as prevention, appraisal, internal failure, external failure.
2. Tag cost entries into one of the four categories as they're incurred, not retroactively from memory.
3. Total each category on a recurring cadence (e.g. monthly).
4. Compare prevention plus appraisal (cost of conformance) against internal plus external failure (cost of nonconformance).
5. Where failure cost dominates, identify which failure category is driving it and evaluate whether targeted prevention or appraisal spend would reduce it.

What it produces

• A running total for each of the four cost-of-quality categories.
• A conformance-versus-nonconformance comparison that argues for or against more upfront quality investment.

Common pitfalls

• Miscategorizing rework as a normal project cost instead of an internal failure cost, which hides the real signal.
• Only counting external failure costs that show up as an invoice (a warranty claim) and missing the ones that show up as reputation or lost repeat business.
• Treating a shrinking failure-cost total as success without checking whether defects are actually down or just being found later, off this project's books.

Worked example

A software team building a billing module tracks $12,000 in prevention (design reviews, static analysis setup), $9,000 in appraisal (QA testing cycles), $31,000 in internal failure (bugs caught and fixed before release), and $4,000 in external failure so far (a production billing error refunded to two customers). With failure costs at $35,000 against $21,000 of conformance spend, the team adds a second design review pass for the next module rather than continuing to absorb the rework.

Source

• PMBOK-6 §8.1.2.3

Where it comes from: this technique is named by the PMBOK Guide, 6th edition.