Stale Defect Percentage
Stale Defect Percentage measures the proportion of open bugs that have not been resolved within a defined time threshold. It reflects how long defects remain in the backlog and highlights the risk of neglected quality issues.
Calculation
A defect is considered “stale” if it has been open longer than a set number of days, commonly 30, 60, or 90. Teams choose the threshold based on SLA targets or product maturity.
The metric is calculated as:
stale defect percentage = number of open bugs older than threshold ÷ total open bugs × 100
Goals
Stale Defect Percentage helps teams surface neglected or deprioritized quality issues. It answers questions like:
- Are we addressing bugs promptly, or letting them sit unresolved?
- Are we meeting our resolution SLAs?
- Is defect volume exceeding our capacity to resolve?
Tracking stale defects supports long-term quality by revealing when issues are silently accumulating and increasing risk.
Variations
Stale Defect Percentage may also be called Old Bug Rate, Aging Defect Ratio, or Overdue Defects. Common breakdowns include:
- By severity, to highlight if high-impact bugs are going stale
- By team or component, to locate neglected areas of the codebase
- By age bracket, such as bugs 30–60 days old vs. 60+ days
- By source, like customer-reported vs. internally found
- By sprint or release, to track regression backlog trends
Some teams pair this with average bug age to create a fuller picture of defect backlog health.
Limitations
This metric tracks age, not urgency. Some low-priority bugs may go stale by design. Conversely, a recent P0 bug may have higher business risk than an old P3.
The metric also assumes accurate ticket aging. Without consistent status updates or closure practices, defect age may be overstated.
To interpret the metric effectively, use it alongside:
| Complementary Metric | Why It’s Relevant |
|---|---|
| Average Bug Backlog Size | Provides context for how big the unresolved pool of issues is overall |
| Bug Closure Rate | Indicates whether stale bugs are being worked down or continuing to accumulate |
| Bug Time Ratio | Reveals whether sufficient capacity is being allocated to fix existing defects |
Optimization
Reducing Stale Defect Percentage requires better triage discipline, resolution prioritization, and backlog hygiene.
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Set review intervals for aging bugs. Use dashboards to flag bugs approaching or exceeding age thresholds
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Define time-based SLAs. Set clear expectations for resolution windows based on severity
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Close non-actionable defects. If a bug won’t be fixed, close or mark it as won’t-fix to keep backlog signals clean
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Prioritize by impact, not just age. Target stale bugs that affect customers or critical systems first
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Use stale bugs as quality signals. High counts may indicate tech debt, unclear ownership, or under resourced teams
Old bugs don’t always cause fires, but they often hide slow leaks. Managing stale defects helps teams deliver with confidence and prevent silent quality decay.
