How can you predict software maintenance cost?
Industry estimates often put annual software maintenance cost at 15-40% of the original development cost. This tool reverse-estimates the initial dev cost from your code size (KLOC), then adjusts the maintenance rate based on codebase age and technical debt level to project an annual cost.
The base maintenance rate starts at 15% and rises 1 percentage point per year of codebase age, capped at 35%. That's then multiplied by a technical debt factor ranging from 0.8x (low debt) to 1.6x (very high debt) to get the final rate. Legacy code with thin test coverage and weak documentation takes far longer to touch, even for the same feature.
Dividing the annual cost by team size gives a rough monthly maintenance burden per developer. If that number vastly exceeds your team's actual capacity for new development, investing in refactoring or paying down technical debt first is usually the more efficient long-term move.
Frequently Asked Questions
Older codebases accumulate legacy dependencies, thinner documentation, and staff turnover, so the same task takes longer over time — pushing the maintenance rate up.
Generally yes. Strong test coverage, refactoring, and documentation reduce the time spent on bug fixes and new features, lowering overall maintenance cost.
This is based on industry average ratios, so treat it as a reference. For actual budgeting, combine it with your team's historical maintenance data.