You ask, “How long will it take?” and the estimate you get back feels like a guess. That moment is where trust often breaks.
This guide is about estimating software development time in a way you can actually use. You will learn why “simple” features swing so much, how teams build estimates, and how to turn effort into a real calendar timeline.
Why is estimating software time so hard?
Many founders picture software like construction. Define the plan, build in order, finish on schedule.
Software rarely works like that. It is full of “unknown unknowns,” small details that show up late and change the work.
Even “standard” features vary a lot. A login screen can mean basic email and password, or it can mean Google sign-in, multi-factor authentication, or enterprise SAML. Each adds new steps, new testing, and more edge cases.
If you want a simple way to get clearer requirements before anyone estimates, start with a product requirements document template. It helps you capture the details that usually get missed in early calls.
Common misconceptions vs what happens in real projects
| What founders often assume | What actually happens |
|---|---|
| “A login is a login, how hard can it be?” | Social sign-on, MFA, password policies, or SAML can double or triple the work. |
| “Third-party APIs are plug-and-play.” | Rate limits, missing docs, and odd auth flows often create delays. |
| “Frameworks are interchangeable.” | Each stack has setup needs, patterns, and trade-offs that affect speed. |
These are not excuses. They are normal parts of custom software work. The goal is to plan for them early, so nobody feels blindsided later.
A real-world login feature breakdown
We once quoted four days for a login flow for a new SaaS product. It finished closer to two weeks.
The original scope was basic email and password. Midway through, the scope expanded to include Google sign-in and enterprise SAML.
“We thought the login would be quick until we hit SAML metadata, certificates, and rotation rules. That’s where the hidden work lived,” a lead engineer told me.
Here is what the work looked like once it was fully defined:
- Basic email/password sign-up: 1 day
- Password reset workflow: 0.5 days
- Google OAuth integration: 2 days
- SAML setup and testing: 5 days (security review plus test coverage)
The first estimate was not “wrong.” It was correct for a smaller feature. The extra time came from added requirements and the risk that comes with enterprise auth.
Small choices that change the schedule
In real builds, tiny decisions can ripple through the entire plan.
- A small database change may require a data migration and backfill.
- A UI library may be missing a key component, so the team has to build it.
- A team new to a stack will move slower at first, even if they are strong engineers.
Hidden work you do not see on a feature list
Most projects have “invisible” tasks under the surface. Examples include data cleanup, refactoring legacy code that must be touched, and adding monitoring so issues show up fast after launch.
These are hard to fully predict up front, even with good planning.
That is why a buffer matters. A 20 to 30% buffer often covers common surprises without turning the plan into a padded wish list.
Before you ask for an estimate, write your core features as short user stories. List integrations, security needs, and any special UI states you already know you want. This one step can save weeks of churn.
Scope for clarity, not just code
Most projects slip before the first line of code. The problem is not effort. The problem is that two people are picturing two different products.
Clear scope creates clear estimates. Vague scope creates numbers you cannot plan a business around.
Turn big ideas into user stories
Founders often say, “I need a user profile.” That sounds simple until you ask what “profile” means.
Does it include a photo? A bio? Social links? Team roles? Admin editing? Privacy controls? Each answer changes the work.
User stories force the details into the open. They also make it easier to prioritize.
- As a user, I can sign up with email and password.
- As a user, I can upload a profile photo.
- As a user, I can edit my bio.
- As a user, I can reset my password.
Now “user profile” is not one big mystery item. It is a set of small items the team can estimate and discuss.
Must-haves vs nice-to-haves
After you list user stories, split them into two buckets.
A must-have is required for the product to work. A nice-to-have adds value, but you can ship without it.
This split is your best defense against scope growth. It also helps you protect launch dates.
Try this simple test for each story:
- Ask, “If we ship without this, can a user still solve the core problem?”
- If the answer is no, it is a must-have.
- If the answer is yes, it is a nice-to-have.
If you are building an MVP, this is even more important. For a step-by-step process, see our MVP development guide for founders.
By the end of scoping, you should have a prioritized list that a team can estimate without guessing what you “really meant.”
Pick an estimation method that fits your stage
Once scope is clearer, you still need a way to attach numbers. There is no single best approach. The right method depends on how defined your product is and how much risk sits in each feature.
T-shirt sizing for early planning
When ideas are still rough, you do not need hour-by-hour estimates. You need scale.
T-shirt sizing assigns a relative size to each feature: S, M, L, XL.
- Small (S): simple work, usually 1 to 3 days
- Medium (M): a few moving parts, often 4 to 10 days
- Large (L): multi-part work, often 2 to 4 weeks
- XL: big slice of a product, often a month or more
This is fast, collaborative, and good for early decisions like, “Is this a 6-week MVP or a 6-month build?”
Story points once a team is shipping
When a team is working in sprints, story points can be a better tool than hours. Points measure relative effort and uncertainty.
The team picks a baseline task and assigns it a value. Other tasks are scored compared to that baseline.
If Feature B feels about twice as hard as Feature A, it gets about twice the points. Consistency matters more than the exact numbers.
Over time, you learn the team’s “velocity,” which helps forecast how much can fit in the next sprint or month.
Three-point estimation for risky work
Some tasks are loaded with unknowns. New tech, messy integrations, or unclear data are common examples.
Three-point estimation forces honesty by capturing a range:
- Optimistic (O): if everything goes right
- Most likely (M): based on normal experience
- Pessimistic (P): if common problems show up
A common PERT formula is:
Estimate = (O + 4M + P) / 6
This pulls the estimate toward “most likely,” but still accounts for risk. It is a good fit when founders want a plan that does not fall apart the first time something unexpected happens.
Turn effort into a real calendar timeline
Let’s say your MVP estimate totals 100 effort-hours.
A common mistake is to divide by 40 hours per week and assume a 2.5-week schedule. Effort-hours are not calendar time.
Work that is not “just coding”
Developers do not spend eight hours a day writing code. Good teams spend time on planning, reviews, and testing because that is how bugs get caught before customers see them.
A realistic schedule includes:
- Project management: planning, coordination, and status updates
- QA: test plans, manual testing, bug fixes, regression checks
- Design and UX reviews: feedback loops, edge states, accessibility checks
- Founder reviews: demos, decisions, and approvals
An effort estimate measures time spent doing the task. A timeline includes the work around the task that makes delivery possible.
If you have never worked with an agency before, our tips for smooth collaboration can help you set expectations early, so timelines do not drift from avoidable miscommunication.
A simple way to do the math
A solid rule of thumb is that focused build time is about 60% of a developer’s week. The rest goes to the activities above.
In a 40-hour week, that is about 24 focused hours.
- Total estimated effort: 100 hours
- Focused dev hours per week: 24 hours
- Timeline: 100 / 24 = 4.17 weeks
Now the plan looks like about a month, not two and a half weeks.
Buffer is not padding
Some founders hear “buffer” and assume it is a hidden fee. A real buffer is a visible way to account for risk.
APIs change. Dependencies break. A “small” feature exposes a deeper data problem. These things happen on good teams too.
For average risk work, a 20% buffer is common:
- Initial timeline: 4.17 weeks
- Buffer: 0.83 weeks
- Total: about 5 weeks
That is a date you can plan around, share with investors, and align marketing to.
If you also need to turn timelines into budget ranges, our software development cost estimation guide is a helpful companion.
Past projects beat guesswork
The best estimates come from real delivery data. If a team has built similar features before, they can anchor your estimate in what actually happened, not what sounds right in a meeting.
For example, if you need an admin dashboard, past dashboards can provide a realistic range. One might have taken 60 hours, another 85, another 110, depending on reporting needs, data sources, and permissions.
The goal is not to find an exact match. The goal is to start from real baselines, then adjust for what is different in your product.
To get better at prediction over time, it helps to learn how teams improve forecast accuracy by tracking results and feeding those results back into planning.
Common questions founders ask
These are the questions that come up in almost every estimation conversation.
“What if the project goes past the estimate?”
It depends on why.
If scope changes, the right move is a clear change request. Pause, define the new work, estimate it, then decide if it ships now or later.
If the work is harder than expected, a good partner flags it early, explains the issue, and offers options. That might mean simplifying a feature, adjusting the timeline, or increasing the buffer for similar items.
“How do you handle scope changes mid-project?”
Change is normal. The problem is untracked change.
A simple process keeps things under control:
- Define it: break the idea into small user stories
- Estimate it: time, cost, and new risks
- Decide: add it now and move the date, or ship it later
“Why can’t I get a simple fixed-price quote?”
Fixed price can work for predictable work, like a basic marketing site.
Custom software is different. To protect themselves, vendors often add a large safety margin. If reality gets messy, the contract can also push teams to cut testing or reduce quality to protect profit.
Many founders do better with a clear scope, a time-based estimate, and steady communication.
“Is the cheapest estimate the best deal?”
Usually not.
A very low estimate often means the scope was misunderstood, testing was skipped, or the team plans to bill change requests for anything not spelled out. The “cheap” option can turn into a rebuild.
Next steps
Estimates get better when the scope is clear, risk is visible, and the timeline includes the work around coding.
If you want help turning your idea into a buildable plan, we can scope it with you and map a realistic timeline. Our build work is supported by our website development services, and we can also support testing, performance, and post-launch improvements through our website optimization services.
When you are ready, plan your strategy call and we will walk through scope, risks, and the timeline together.
