Understanding Defect Leakage
How we calculate. Leakage % = (post-release defects ÷ total defects) × 100 — keep the same defect definition in both counts. See our methodology and accuracy policy .
Real-world scenario: A typical Defect Leakage case uses defects found after release 8 and total defects found (all phases) 80. Enter the same figures below to reproduce the worked path.
What is Defect Leakage?
Defect leakage is the share of all discovered defects that slipped past earlier QA phases. Teams use it to judge whether unit, integration, and system testing are catching issues before release.
- Target: many teams aim for leakage under 5–10%, depending on product risk
- Not the same as density: leakage is a phase-escape rate; density is defects per size unit
- Count consistently: include only confirmed defects, not duplicate tickets
The Formula
Worked Example
Common Use Cases
- Release retrospectives: compare leakage sprint to sprint
- Test process audits: high leakage points to weak earlier phases
- Vendor / outsourced QA: track escapes into your production environment
Pro Tips
- Split by severity: critical escapes matter more than cosmetic ones
- Exclude rejected tickets: invalid defects inflate totals
- Pair with DRE: leakage and DRE tell complementary stories
| Scenario | When to use |
|---|---|
| Percent of a number | Finding a part of a whole (tax, tip, score) |
| Percent change | Comparing old vs new values |
Limitations: Defect Leakage results are estimates for learning and QA planning—not contractual SLAs. Align definitions with your org’s quality glossary before executive reporting.
Common mistakes
- Swapping part and whole: The denominator must be the full total, not a subset.
- Rounding too early: Carry extra decimal places through multi-step work before rounding the final percent.
- Mixing percent and decimal forms: Enter rates in the format the calculator labels expect.
The worked example for defect leakage was verified with the calculator form on this page—enter the same values to confirm the result.
When to use this calculator
- Use this page when your wording matches defect leakage and the form labels on screen.
- Use percent of a number for “what is X% of Y?” problems.
- Use number is what percent when you know part and whole and need the percent.
Still unsure about defect leakage? Start with the quick answer above, then open the linked calculator that matches your wording.
❓ Frequently Asked Questions
How do I use this defect leakage calculator?
For defect leakage, enter the values labeled on the form, then press Calculate. Compare the result to the worked example on this page.
What formula does this page use?
See the quick answer and formula box above for defect leakage—the same percentage calculator expression is applied to your inputs.
What if my result looks wrong?
When checking defect leakage, re-check part vs whole (or rate vs base), rounding, and whether percents were entered as 25 rather than 0.25 when the form expects percents.
Authoritative References
For software quality metrics definitions, consult established engineering sources:
- ISTQB — software testing glossary and practices
- ISO/IEC 25010 — systems and software quality models
- IEEE — software engineering standards