Development Estimation - An interesting chat
Prompt
You are a senior software engineer and you are asked to estimate on a piece of work that you know will take you 4 hours to complete, what is the estimate that you give to the client?
As a senior software engineer, when estimating a task that I know will take me 4 hours to complete, I would typically provide an estimate to the client that includes a buffer for unforeseen issues, communication overhead, and potential scope changes. A common practice is to multiply the actual effort by a factor, often ranging from 1.5x to 3x, depending on the complexity, risk, and client relationship.
Given this, an estimate I might provide for a 4-hour task could be in the range of:
- 6 hours (1.5x buffer): This would be for a very well-defined task with low risk, where I have high confidence in the initial 4-hour assessment and minimal external dependencies.
- 8 hours (2x buffer): This is a more common and generally safer estimate. It accounts for minor disruptions, a reasonable amount of communication, and a small margin for unexpected complexities.
- 10-12 hours (2.5x to 3x buffer): This would be for tasks with some ambiguity, potential for client feedback cycles, or dependencies on other teams/systems that might introduce delays.
My rationale for adding a buffer includes:
- Unexpected Issues: Even seemingly straightforward tasks can encounter unforeseen bugs, integration problems, or environment setup issues.
- Communication and Meetings: Time is spent in meetings, clarifying requirements, providing updates, and responding to client queries.
- Context Switching: If I’m working on multiple tasks, there’s a cognitive cost and time loss associated with switching between them.
- Testing and QA: The 4 hours might be for coding, but thorough testing and potential bug fixes are also part of the work.
- Documentation: Creating or updating any necessary documentation.
- Learning/Research: If there’s any new technology or unfamiliar part of the codebase involved, some time might be needed for learning.
- Client Feedback and Revisions: Clients often have feedback, which can lead to further iterations.
- Burnout Prevention: Aggressive estimates can lead to rushing, lower quality, and increased stress.
When communicating the estimate to the client, I would also:
- Explain the assumptions: Briefly state what is included and excluded from the estimate.
- Offer a range (if appropriate): Sometimes, providing a “best-case to worst-case” range can be helpful, e.g., “I anticipate this will take between 6 and 8 hours.”
- Emphasize flexibility: Let them know that if new information or changes arise, the estimate may need to be revised.
- Focus on value: Frame the estimate in terms of delivering a quality solution, not just raw hours.
In most scenarios, I would lean towards an 8-hour estimate for a task I anticipate taking 4 hours of pure, uninterrupted coding. This provides a reasonable buffer without appearing overly conservative, and it helps manage client expectations effectively.
Prompt
if you could, based on the reasons above, extrapolate a algorithm to get to the estimate, with the reasons being a percentage of the original development estimate
Algorithm for Software Estimation (Percentage-Based)
1. Define Your Base Estimate (Pure Development Time - PDT):
- This is your ideal, uninterrupted, head-down coding/development time.
- Let’s call this value PDT.
2. Identify and Quantify Buffer Categories (as percentages of PDT):
- Assign a percentage range or a default percentage to each common overhead/risk category. These percentages are subjective and should be refined over time based on your team’s experience and project types.
Here are common categories and example percentages:
- a. Unforeseen Issues/Bug Fixing (UIF): Account for unexpected technical challenges, bugs, or refactoring needed during development.
- Typical Range: 10% - 30%
- Default (Average Risk): 20% of PDT
- b. Communication & Meetings (CM): Time spent in stand-ups, client meetings, internal discussions, email, clarification, etc.
- Typical Range: 5% - 15%
- Default: 10% of PDT
- c. Testing & Quality Assurance (TQA): Time for unit testing, integration testing, manual QA, and potential re-work after testing.
- Typical Range: 10% - 25% (Can be higher for critical systems)
- Default: 15% of PDT
- d. Context Switching & Distractions (CSD): Time lost due to switching between tasks, minor interruptions, or non-project related activities.
- Typical Range: 5% - 15%
- Default: 10% of PDT
- e. Documentation & Knowledge Transfer (DKT): Time for updating existing docs or creating new ones.
- Typical Range: 2% - 8%
- Default: 5% of PDT
- f. Learning/Research (LR): If the task involves new technologies, unfamiliar codebases, or complex problem-solving. (This might be highly variable; consider it only if applicable).
- Typical Range: 0% - 20% (If applicable)
- Default: 0% (Assume this is part of PDT unless specifically complex)
- g. Client Feedback & Iterations (CFI): Time for incorporating client feedback and performing minor revisions.
- Typical Range: 5% - 20% (Higher for less defined projects)
- Default: 10% of PDT
3. Calculate the Total Buffer Percentage (TBP):
- Sum the chosen percentages for each applicable buffer category.
- TBP=UIF%+CM%+TQA%+CSD%+DKT%+LR%+CFI%
4. Calculate the Final Estimate (FE):
- The final estimate is the Pure Development Time plus the total buffer.
- FE=PDT+(PDT×TBP)
- Or, more simply: FE=PDT×(1+TBP)
Example Application of the Algorithm:
Let’s use the example of a 4-hour PDT:
- PDT=4 hours
Now, let’s select our default buffer percentages:
- UIF = 20%
- CM = 10%
- TQA = 15%
- CSD = 10%
- DKT = 5%
- LR = 0% (assuming no specific learning for this small task)
- CFI = 10%
Calculate TBP: TBP=0.20+0.10+0.15+0.10+0.05+0.00+0.10=0.70 or 70%
Calculate FE: FE=4×(1+0.70) FE=4×1.70 FE=6.8 hours
Rounding up for practicality, this would likely be 7 or 8 hours. This aligns well with the 1.5x to 2x multiplier (6-8 hours) discussed previously for a low-to-medium risk 4-hour task.
Example for a 12-hour PDT:
- PDT=12 hours
- Let’s keep the same default buffer percentages, as they represent general overheads.
- TBP=0.70 or 70%
Calculate FE: FE=12×(1+0.70) FE=12×1.70 FE=20.4 hours
Rounding up, this would likely be 21 hours. This is slightly less than the 24 hours (2x multiplier) I commonly suggested. The difference highlights that a fixed percentage sum might lead to slightly less than a pure 2x multiplier. If I consistently use a 2x multiplier for 12 hours, it implies a total buffer of 100%.
Refining the Algorithm Based on Experience:
If you consistently find that a simple 2x multiplier works well for “average” tasks, it means your implicit total buffer percentage for average tasks is 100%. You could then work backward to adjust your individual buffer category percentages to sum closer to 100%.
For instance, to achieve a 2x multiplier (100% buffer):
- UIF: 25%
- CM: 15%
- TQA: 20%
- CSD: 15%
- DKT: 10%
- CFI: 15%
- Total = 100%
This demonstrates how you can customize these percentages based on your specific team, project type, and risk tolerance. The key is to make these percentages explicit and review them periodically.
Final Algorithm Summary:
- Determine Pure Development Time (PDT).
- Assess Risk/Complexity: For each buffer category, select a percentage within its typical range based on the specific task’s characteristics.
- Sum all selected percentages to get the Total Buffer Percentage (TBP).
- Calculate Final Estimate (FE) = PDT * (1 + TBP).
- Review and Adjust: Apply common sense and consider rounding up to practical increments (e.g., half-days or full days). Always be prepared to explain the components of your estimate to the client.
Gemini - Software Estimation: Buffer and Rationale