The Lucky Days Sizing Guide for Development Estimations


In the realm of software development, estimating the time and effort required for tasks is both an art and a science. The Lucky Days Sizing Guide offers a fresh perspective on this challenge, introducing a methodology that balances precision with flexibility. This guide is designed to foster a common understanding among delivery teams, while also accommodating the inherent uncertainties of development work.

Sizing Categories

The guide categorizes tasks into three sizes, each represented by "Lucky Days," which serve as a measure of estimated effort:

  • Small Tasks: 1 - 2 Lucky Days
  • Medium Tasks: 3 - 6 Lucky Days
  • Large Tasks: 7 - 14 Lucky Days

These categories are intentionally broad to encourage commitment without the pressure of over-analysis. By doing so, teams can focus on progress rather than getting bogged down in the minutiae of estimation.

Methodological Approach

Baseline Establishment

The Lucky Days concept employs days as a universal metric, understandable by all team members, while simultaneously introducing an abstract layer to prevent over-specification. This duality enables teams to align their expectations and work towards a common goal.

Ranges Over Specifics

A key feature of this methodology is its use of ranges rather than exact figures. These ranges widen with the scale of the task to naturally incorporate the increased risk and uncertainty associated with larger endeavors. This approach acknowledges the complexity and unpredictability inherent in software development, allowing for flexibility and adjustment as projects progress.

Conversion and Application

For situations requiring a more concrete timeline, such as fixed-price billing, project managers can convert these sizes into actual days. This conversion is based on a statistical analysis of the team's velocity—essentially, how many Lucky Days are completed within a real-world day. By leveraging historical data and performance metrics, project managers can establish a more accurate and realistic schedule.

This strategy mitigates the impact of "fear bias"—the tendency to overestimate work to avoid potential underdelivery—and distributes risk more evenly between the delivery team and project managers. It’s a pragmatic approach that recognizes the challenges of estimation while striving for accountability and efficiency.


The Lucky Days Sizing Guide represents a novel approach to the perennial challenge of development estimation. By blending abstract sizing with concrete data, it offers a pathway to more reliable and consensus-driven estimates. This methodology not only enhances the planning and execution of projects but also supports a healthier, more collaborative relationship between delivery teams and project management. As the software development landscape continues to evolve, adopting flexible and innovative estimation techniques like the Lucky Days Sizing Guide will be key to navigating the complexities of project delivery with confidence and success.