Almost every buyer has seen it: a quote that looked fair, a project that cost more and took longer. Estimates run low often enough that many buyers distrust every quote before they read it. That distrust is reasonable, but it is also fixable. Most low estimates come from a handful of causes, and a good estimate shows its working.
This guide explains why software estimates run low and what a reliable estimate contains, so you can judge a quote before you sign. For the numbers behind a typical build, see what a SaaS MVP costs in 2026.
Why Estimates Run Low
They assume the happy path
An estimate for "user login" often covers the form and the database table. It leaves out password reset, failed attempts, email verification, session expiry and the admin view. Each is small. Together they can double the work.
They miss work that is not coding
Design, project management, testing, deployment, documentation and bug fixing are real hours. A quote that lists only development leaves them to appear later as extra charges.
Unknowns are priced at zero
Third-party APIs, existing systems and unclear requirements hide surprises. When an estimator does not know how an integration behaves, the easy move is to assume it is easy.
Selling pressure pushes the number down
A lower quote wins the deal. If the agency expects to recover the difference through change requests, the low estimate was a sales tool and not a forecast.
Scope is described, not defined
"A dashboard" can be one chart or twenty. When the scope is a sentence, both sides read it in their own favour.
One number hides the uncertainty
A single figure suggests precision that does not exist. Real estimates have a range, and the range is wider early in the project.
What a Reliable Estimate Contains
A range, not a point. Something like "ten to fourteen weeks" tells you how much the team does not yet know.
A breakdown. Estimates split by feature or phase let you see where the budget goes and which parts are uncertain. A single lump sum hides this.
Listed assumptions. Good estimates say what they assume: the number of user roles, which integrations are included, who provides content and how fast feedback arrives. When an assumption breaks, the change in price is easy to explain.
Named exclusions. Hosting, third-party licence fees, content and post-launch support should be written down as included or not.
A basis in past work. Ask which previous projects the estimate draws on. Experience with similar products is the best predictor.
An agreed way to handle change. The contract should state how scope changes are priced and approved. See our list of questions to ask a software agency before signing.
The Most Reliable Fix: Pay for Discovery First
The accuracy of an estimate depends on how much is known when it is written. A short paid discovery phase turns vague requirements into a defined scope, a prioritised backlog and a list of technical risks. The estimate that follows is narrower and easier to trust. Read more in what a software discovery phase produces.
How to Check an Estimate You Have Received
- Ask for a breakdown if you received a single figure.
- Ask what is excluded.
- Ask which three items are most likely to take longer, and why.
- Ask for the rate and process for extra work.
- Compare it with other quotes by inclusions, not only by total. Our checklist for evaluating a software development company shows how.
Frequently Asked Questions (FAQs)
Is a fixed price a reliable estimate?
A fixed price moves the risk of overruns to the agency, but it only works when the scope is well defined. Check what is excluded and how changes are handled, because that is where the extra cost returns.
How much should I add as a buffer?
Many teams add a contingency on top of the estimate for the unknowns. The size should reflect how much is still undefined: smaller after discovery, larger before it.
Why do timelines run late as well as budgets?
For the same reasons: hidden work, unknowns and scope growth. Our guide to how long it takes to build a SaaS platform breaks a schedule into phases.
Conclusion
Estimates run low when they assume the best case, skip non-coding work and hide uncertainty. A reliable one shows a range, a breakdown, its assumptions and its exclusions, and it is written after discovery, not before.
If you want a scoped estimate for your project, see our custom software development services or get in touch.