Improving Estimations in Software Development Projects: Why It’s So Hard and How to Get It Right

Software Development is, at its core, a mix between math and logic. But if math is an exact science, Software development isn’t.

Improving Estimations in Software Development

Software development is often seen as a balance between math and logic, but while math is an exact science, software development is far from it. Estimating how long it will take to deliver a feature or complete a project is one of the most challenging tasks for developers, project managers, and stakeholders alike.

According to the Standish Group’s 2015 CHAOS report, only 36% of software projects successfully met their scope, time, and cost goals. Meanwhile, 45% of projects were challenged, and a staggering 19% failed entirely. The same report highlights that 60% of project estimations are inaccurate, often leading to delays, budget overruns, and even project failure. [1]

With such high stakes, improving your estimation skills becomes crucial for successful software project delivery. In this article, we’ll explore what estimations really are, why they matter, and how you can make them more accurate using practical techniques and strategies.

TL;DR: A Simple Approach to Better Estimations

Imagine a scenario where your team has estimated the effort for a particular development task to be ten sprints or weeks (or your preferred unit of time). To make that estimation more reliable, do the following:

Add [20 to 30]% of unforeseen work

This is pure risk management. No matter how much planning you do, the unexpected will occur. Adding 20–30% buffer time accounts for these surprises.

From:

Total: 10

To:

Total: 12/13

If the task is simple or your team is highly experienced, you might reduce this buffer, but never go below 10%. Even in the best case, unforeseen issues can arise.

Add [20 to 30%] for additional delivery work

Beyond development, consider tasks like User Acceptance Testing (UAT), production deployments, and bug fixes, which can add time to your overall delivery.

From:

Total: 13/14

To:

Total: 16/18

I usually have a fixed estimation for the deployment while using a percentage for the tests.

For simpler projects, go with the lower estimate of 16 sprints. For more complex projects, use the higher end of 18 sprints. The key is to consistently account for testing and deployment time rather than treating them as afterthoughts.

Why You Should Stick to Your Buffer Time

You’ll likely be asked why something estimated at ten sprints now requires 16 or even 18. It’s essential to explain that the actual development effort hasn’t increased, but the new estimate accounts for the entire delivery process, including testing, debugging, and deployment, which were previously left out.

Additionally, some tasks may require less than the full capacity of your team, meaning they can work on other tasks in parallel. However, cutting time strictly based on optimistic assumptions increases the risk of delays, rework, or even failure.

If there are strict time constraints, you have two viable options:

Reduce the scope and split the work into multiple smaller deliverables. This allows for better adaptation to changes and helps manage expectations.
If scope is non-negotiable, openly share the risk. Make it clear that all stakeholders (engineering, product, and business teams) should align on the risks of choosing an optimistic timeline.

Also consider Progressive Elaboration — Start with high-level estimates and refine them as more information becomes available. This approach is ideal for long-term projects where early-stage unknowns may skew initial estimates.

Why Do Estimations Fail?

Most project estimations fail for three key reasons: misalignment on what’s being estimated, only estimating known tasks, and the desire to please stakeholders.

1. Align on What You’re Estimating

By default, each person involved in a project may have a different understanding of what needs to be done. Without clarity, estimations will inevitably fail. For example, if someone asks, “How long will it take to change the login form to add a CAPTCHA?” you might think, “A couple of hours.”

However, it’s important to recognize that development is only part of the delivery process. After coding, the changes need to be tested, integrated, and deployed. The real question is not “How long will it take to write the code?” but “When can this feature be live in production?”

To avoid confusion, always ensure there’s a shared understanding of the scope and definition of done. Estimating without this alignment is one of the quickest ways to miss deadlines.

You can learn more about the Definition of Done here.

2. Treat the Unknown as a Risk

You cannot estimate what you don’t know. However, rather than guessing, treat these unknowns as risks that can be managed.

For simple tasks, unexpected issues are less likely to occur. But when dealing with more complex work, the likelihood of encountering unforeseen challenges increases. For example, you might split the login form work into sub-tasks: username/password fields, social login, CAPTCHA, etc. You can estimate these individual pieces fairly well.

However, while developing the form, you discover that configuring social logins requires external team involvement. The longer the project, the more likely such dependencies will appear.

This is why adding slack time proportional to the project’s complexity is critical. The more complex the task, the higher the chances of encountering something that extends the timeline.

3. Don’t Be a Pleaser

It’s natural to want to deliver results quickly, especially when pressured by stakeholders. However, cutting time to please others is a recipe for failure. By being overly optimistic, you push the risk of delays further down the line. Instead of focusing on delivering quality, you’ll find yourself constantly explaining delays and replanning.

Many organizations fall into a trap of chronic replanning, as described by Ben “The Hosk” Hosking in his article, “How Much Money Has Been Lost on Software Projects That Keep Replanning and Missing Deadlines”. By trying to please, you end up causing more problems than you solve.

If you’re working with tight deadlines, consider the following:

Cut scope or break the work into smaller deliverables.
Face reality and share the risks with stakeholders. It’s better to be realistic than overly optimistic.

Managing Stakeholder Expectations

A crucial part of delivering successful projects is managing expectations. When you provide an estimate, make sure you explain the assumptions, risks, and potential blockers that could impact the timeline. This level of transparency builds trust with stakeholders and reduces the likelihood of surprises later on.

Additionally, ensure that everyone understands that an estimate is not a commitment. It’s a calculated guess based on known factors, which will be adjusted as new information comes to light.

Conclusion: Improving Estimations is Key to Project Success

Estimation is one of the most critical aspects of project planning in software development, yet it’s also one of the most challenging. By accounting for risk, complexity, and the full delivery cycle, you can create more accurate estimates that stakeholders can rely on.

Remember, the goal is not to give the shortest possible timeline but to provide a realistic timeline with a high probability of success. Apply the techniques discussed here — adding slack time, breaking down complex tasks, and managing unknowns — and you’ll see improvements in both estimation accuracy and project outcomes.

If you’re interested in learning more, check out Dave Stewart’s article, “The Work is Never Just ‘The Work’” for further insights into estimation and project planning.