“We can have this live in 3 months.”
This is the most dangerous sentence in software development.
You sign the contract based on that promise. Three months later, the features are only 60% done, the budget is burning, and you are having difficult conversations with stakeholders.
Why does this happen so often? Is the team lazy? Are the developers slow?
Almost never. The problem is not the work ethic. The problem is the math.
Most agencies create a project timeline based on optimism and “happy path” scenarios. They confuse the hours needed to code (effort) with the weeks needed to deliver (duration).
This guide explains the critical difference between a software estimate and a project timeline, and how to calculate a launch date you can actually trust.
Table of Contents
- The estimation gap: Effort vs. Duration
- Mistake 1: The “8-hour day” fallacy
- Mistake 2: Ignoring the feedback loops
- Mistake 3: Planning strictly linearly
- How to build a realistic timeline (The 3-step formula)
- How devtimate helps you calculate reality
- Checklist
- FAQ
The estimation gap: Effort vs. Duration
This is where 90% of timelines fail.
Your developers estimate a feature, say “User Profiles,” will take 40 hours of work. You (or the Project Manager) look at the calendar and think: “Great, one developer works 40 hours a week. That feature will be done in 1 week.”
This is mathematically correct but practically impossible.
Effort is the raw time needed to write the code if the developer is locked in a quiet room with no interruptions. Duration is how long that work takes in the real world.
In reality, a 40-hour task takes about 2 to 2.5 weeks to complete. Why? Because of the hidden friction that most estimates ignore.
Mistake 1: The “8-hour day” fallacy
No developer codes for 8 hours a day.
If you plan your timeline assuming 100% capacity, you are guaranteed to fall behind on day one. A typical senior developer spends time on:
- Daily stand-up meetings
- Code reviews for other team members
- Context switching
- Clarifying requirements with the PM
- Fixing minor bugs from previous sprints
The Fix: Plan for 5 to 6 hours of effective coding work per day, maximum. If your software estimate says 100 hours, do not divide it by 40 (weeks). Divide it by 25 or 30 to get a realistic timeline.
Mistake 2: Ignoring the feedback loops
Writing the code is only half the job. The other half is verifying it.
A common timeline mistake is creating a schedule that looks like this: Week 1: Build Feature A Week 2: Build Feature B Week 3: Build Feature C
This assumes Feature A is perfect the moment it is finished. It never is.
Real software development requires a feedback loop:
- Developer builds Feature A.
- QA (Quality Assurance) tests it.
- QA finds a bug.
- Developer fixes the bug.
- Client (you) reviews it and asks for a tweak.
- Developer implements the tweak.
If your timeline does not have dedicated buffers for QA and User Acceptance Testing (UAT), you aren’t building a plan. You are building a wish list.
Mistake 3: Planning strictly linearly
Some timelines are too pessimistic because they assume everything must happen in a sequence.
- “Design must be 100% done before Backend starts.”
- “Backend must be 100% done before Frontend starts.”
This creates the “Waterfall” trap. If the Design phase is delayed by two days, the entire project launch is delayed by two days.
The Fix: Modern software teams use Agile workflows. Once the design for “User Profiles” is approved, the developers start building it while the designers move on to “Checkout.” A good project timeline overlaps these phases to save time without sacrificing quality.
How to build a realistic timeline (The 3-step formula)
To get a launch date you can present to your board with confidence, follow this formula.
Step 1: Get a granular estimate
Do not estimate the whole project. Break it down into small features (e.g., “Login,” “Search,” “Filters”). Estimate the hours for each role: Design, Frontend, Backend.
Step 2: Apply the “Focus Factor”
Take the total hours and divide them by a realistic weekly capacity (e.g., 30 hours per developer, not 40).
- Example: 300 hours of effort / 30 hours per week = 10 weeks duration (for one developer).
Step 3: Add the “Process Tax”
Add distinct blocks of time on top of development for:
- Project Management: Usually 10-15% of total hours.
- QA/Testing: Usually 20-30% of development hours.
- Buffer: Add 15-20% for “unknown unknowns” (like API issues or illness).
The final number will be higher than you “hoped,” but it will be a deadline you can actually hit.
How devtimate helps you calculate reality
You cannot build a good timeline on a bad estimate.
If your initial numbers are guesses, your timeline is fiction. This is why agencies use devtimate to ground their planning in data.
devtimate forces you to think about the hidden factors before you commit to a date.
- Separate Roles: It separates Frontend, Backend, QA, and PM hours automatically. You see exactly how much non-coding work is required.
- Risk Ranges: Instead of a single number, devtimate uses Optimistic/Pessimistic ranges. You can build your timeline based on the “Realistic” or “Pessimistic” scenario to be safe.
- Visual Breakdown: You can see which modules are the heaviest. If “Admin Panel” takes 400 hours, you know immediately that you need to assign more resources there or move it later in the timeline.
By starting with a structured, detailed estimate in devtimate, you give your Project Manager the raw data they need to build a winning schedule.
Start your realistic plan with devtimate.
Checklist
✅ Do not confuse effort (hours) with duration (weeks).
✅ Assume developers have only 5-6 effective coding hours per day.
✅ Include specific timeline buffers for QA and bug fixing.
✅ Plan for client feedback delays (e.g., 2 days for approval).
✅ Ensure your estimate includes Project Management time (10-15%).
✅ Use a range-based estimate to account for technical risks.
FAQ
1. What is the difference between a project timeline and a roadmap?
A timeline is a specific schedule with dates and deadlines for tasks. A roadmap is a high-level strategic document that shows the direction and priorities of the product over time, often without specific dates.
2. Why does adding more developers not always speed up the timeline?
This is known as “Brooks’s Law.” Adding manpower to a late software project makes it later. New people need training, which takes time away from existing team members. Communication complexity also increases, slowing down decision-making.
3. How much buffer should I add to my software timeline?
For a standard project with clear requirements, a 20% buffer is recommended. If you are working with new technology or unclear requirements (no discovery phase), you should add a 30-50% buffer to the timeline.
4. Can devtimate create a Gantt chart?
No, devtimate is a specialized estimation tool. It provides the accurate data (hours, roles, costs) that you feed into a project management tool (like Jira, Asana, or Monday) to create a reliable Gantt chart.
5. What happens if we miss a deadline on the timeline?
In a professional setup, the timeline is reviewed weekly. If a delay happens, you have three options: extend the deadline, increase the budget (to add senior resources carefully), or reduce the scope (cut low-priority features) to hit the date.
A missed deadline costs more than money. It costs trust.
By understanding the science of the project timeline, you stop making promises you can’t keep and start delivering on time, every time.
It all starts with the right numbers. Use devtimate to get your estimation right, so your timeline can follow.
