COCOMO

COCOMO (Constructive Cost Model) is a family of software cost estimation models that predict effort, schedule, and cost for software projects. Developed by Barry Boehm in the early 1980s, it provides a parametric approach in which total effort is a function of program size and a set of cost drivers.

COCOMO I consists of Basic, Intermediate, and Detailed models. All variants use size measured in thousands of delivered source lines of code (KLOC) and adjust for product, platform, personnel, and project attributes. The basic model yields rough estimates of effort and duration; the intermediate model adds a larger set of cost drivers; the detailed model further refines by distributing effort across development phases using an iterative approach.

Inputs include project size (KLOC) and ratings for numerous cost drivers. Outputs include estimated effort (person-months), development time, staffing, and potentially a breakdown by phase. The core idea is that effort is a function of size multiplied by an overall effort multiplier derived from the cost drivers.

COCOMO II, introduced to address modern software development, reuse, and process practices, updates the original model with new scale factors and cost drivers. It accommodates software components, reuse, and rapid development; estimates are expressed similarly in person-months and schedule, but with updated calibration constants.

Usage and limitations: COCOMO is widely taught and used for early-stage budgeting and project planning, but its accuracy depends on data calibration to an organization and project type. It may be less reliable for projects that rely heavily on rapid prototyping, agile methods, or extensive reuse without careful tuning. Accurate size estimation and historically grounded data improve predictive performance.