How do I evaluate developer estimates to know if they're realistic?

Why most estimates feel opaque

Developers often quote a total number because it is faster to produce and easier to sell. The problem is that a single figure hides all the decisions and risks underneath it. When something shifts — a third-party API behaves differently, a requirement is ambiguous — there is no shared reference point for why the number changes. A transparent estimate is a negotiating document, not just a price tag.

What a credible estimate includes

• Feature-level breakdown: Each distinct piece of functionality should carry its own hours or days, with a range (best case / likely / worst case), not a single number.
• Non-feature work itemised: Look for explicit line items covering code review, QA and testing, DevOps or deployment setup, third-party integrations, and documentation. If these are absent, they are either hidden inside the feature lines or not planned at all.
• Stated assumptions: A good estimate lists what it assumes — for example, design assets are ready, the API is documented, a staging environment exists. Every unchecked assumption is a future change order.
• Exclusions listed: Knowing what is not in scope is as valuable as knowing what is.

Questions to ask before accepting an estimate

1. "Can you walk me through the biggest uncertainty in this estimate?" A team that cannot name a risk probably has not thought it through.
2. "What have you built that is closest to this?" Ask for a past project of similar scope, ideally with a reference you can contact.
3. "What causes estimates like this to grow, and by how much?" Experienced teams know their historical overrun patterns.
4. "What decisions do we need to make in the next two weeks that could change this number?" This surfaces hidden dependencies early.
5. "How are change requests handled?" Fixed-price and time-and-materials contracts handle scope changes differently — know which one you are signing.

Spotting common warning signs

How milestone-based pricing helps

One practical safeguard is milestone-based contracts: you pay on delivery of defined, working functionality rather than by calendar month. This aligns the team's incentive with output, and gives you natural checkpoints to reassess. Studios like CodeNicely structure work this way — with scoped milestones and client IP ownership — which makes estimates easier to verify because each milestone has an acceptance criterion attached to it.

When estimates differ wildly between vendors

A large spread usually means the vendors are not pricing the same scope. Before comparing numbers, make sure each team is reacting to the same written specification. If you do not have a spec yet, a paid discovery or scoping engagement — typically a few days to two weeks — is worth the investment before you commit to build.