Fixed price or time and materials. It's the question every web agency director asks at some point -- usually after a project that spiralled, a margin that melted, or a client who disputed the final invoice. Choosing a billing model isn't just an administrative matter. It's a strategic decision that directly impacts your profitability, your client relationship, and the way your teams work day to day.
And yet, in the majority of web agencies, this choice is made by default. You do fixed price because you've always done fixed price. Or you do time and materials because a competitor does. Without any real analysis of what works best for each situation.
This article details the advantages, risks, and concrete use cases for each billing model. It also proposes a third model -- the hybrid fixed price with milestones -- that combines the best of both worlds.
Fixed Price: Simple on the Surface, Risky Without Tracking
Fixed price is the most common billing model in web agencies. The principle is simple: a set price for a defined scope. The client knows exactly how much they'll pay. The agency knows exactly how much they'll invoice. Everyone's happy -- in theory.
The Real Advantages of Fixed Price
Clients love it. Fixed price meets the fundamental need for budget predictability. A marketing director who needs to get a budget approved by the executive committee needs a number, not a range. Fixed price provides that number.
The sale is simpler. Comparing a fixed price quote of EUR 15,000 with a competing quote of EUR 18,000 is immediate. Comparing a daily rate of EUR 650 with another of EUR 720 without knowing the number of days is far more complex. Fixed price facilitates the buying decision.
The agency controls its schedule. A fixed price implies upfront scope and timeline definition. This scoping forces early-stage thinking that structures the project and allows resource planning with greater certainty.
The Major Risks of Fixed Price
Scope creep is your mortal enemy. With fixed price, every additional client request that wasn't in the specifications reduces your margin. And these requests always come. "Could we also add a filter on the product page?" "Actually, we'd like a slider instead of a static image." "Can we integrate the Instagram feed?" Each of these requests represents 2 to 8 hours of work. Multiplied by ten over the course of the project, that's 20 to 80 hours given away. On a 150-hour project, that's 13 to 53% overrun.
Concrete example: An agency signs an e-commerce site at fixed price for EUR 22,000, estimated at 220 hours. The client is responsive, back-and-forth is frequent. "Minor" requests pile up: checkout flow modification, additional shipping methods not originally scoped, extensive product page customization. At delivery, the project has consumed 305 hours. The actual cost to the agency: EUR 30,500 (at EUR 100/hour). The net loss: EUR 8,500 on a project sold for EUR 22,000. The margin goes from +30% to -28%.
Specifications are rarely exhaustive. Even with the best specifications in the world, grey areas remain. "Content integration" -- content provided by the client in Word with random formatting, or structured content in a clean Google Doc? "Responsive site" -- responsive across the 3 standard breakpoints, or optimized for the 12 screen sizes the client will test on their personal phone?
Deadline pressure compresses quality. When the agency realizes mid-project that hours are flying, the temptation is strong to reduce testing, simplify integration, and deploy "as is." Fixed price creates a perverse incentive: doing worse to stay within budget.
When Fixed Price Works Well
Fixed price is appropriate when three conditions are met:
- The scope is perfectly defined and the client commits to not modifying it without a change order.
- The agency has already completed similar projects and has reliable historical data for time estimation.
- A mechanism for managing scope changes and scope creep is contractually provided (change order process, formal approval of additional requests).
Time & Materials: Transparent but Hard to Sell
Time and materials, or billing based on actual time spent, consists of billing the client based on hours actually consumed, typically at an agreed daily or hourly rate. The agency doesn't commit to a total price, but to a unit cost.
The Real Advantages of Time & Materials
Profitability is protected by design. Every hour worked is billed. There are no "gifts" to the client, no silent overruns. If the project takes 150 hours instead of 120, the additional 30 hours are billed. Unit margin is preserved regardless of the final scope.
Flexibility is maximized. The client can change their mind, add features, revise priorities mid-project. With time and materials, this is not only possible but natural. The team works on whatever has the most value at any given moment, without being trapped by rigid specifications.
The client relationship is healthier. With fixed price, every additional request creates tension: the client wants more, the agency wants to limit. With time and materials, this tension disappears. The client asks, the team delivers, the hours are billed. The discussion focuses on priorities, not scope boundaries.
Quality isn't sacrificed. The team has time to do things right. No pressure to rush testing or simplify integration. Time devoted to quality is billed just like production time.
The Real Difficulties of Time & Materials
Clients fear the open-ended bill. "What if it takes twice as long as expected?" That's the first objection, and it's legitimate. Time and materials transfers the financial risk to the client, which creates natural anxiety.
The sale is more complex. Selling a daily rate of EUR 700 with no commitment to results requires prior trust that new clients don't yet have. Time and materials is easier to sell to an existing client than to a prospect.
Tracking is non-negotiable. With time and materials, the client expects total transparency on hours consumed. Regular, detailed, incontestable activity reports. Without a rigorous time tracking tool, time and materials becomes a source of permanent disputes.
Key takeaway: Time and materials isn't a billing model "for disorganized agencies." On the contrary, it's the model that demands the most rigor in tracking and reporting. Without reliable data, client trust erodes within a few weeks.
When Time & Materials Works Well
Time and materials is appropriate when:
- The scope can't be locked down upfront (innovation project, progressive redesign, ongoing support).
- The client has an agile mindset and understands that the budget is a continuous investment, not a fixed price.
- A trust relationship is established, typically after a first fixed-price project that went well.
The Hybrid Model: Fixed Price with Milestones and Alerts
The reality is that neither pure fixed price nor pure time and materials suits every situation. The hybrid model combines the strengths of both approaches by segmenting the project into phases billed at fixed price, with built-in flexibility mechanisms.
The Milestone-Based Fixed Price Principle
The project is broken down into 3 to 5 phases (scoping, mockups, development, testing, deployment). Each phase has its own fixed price with its own deliverables and budget. At the end of each phase, a validation checkpoint allows adjusting the scope and budget for the next phase.
| Phase | Deliverable | Fixed price budget | Decision point |
|---|---|---|---|
| Scoping and brief | Validated specifications | EUR 2,500 | Specs validation before mockups |
| Art direction | Desktop + mobile mockups | EUR 4,500 | Mockups validation before dev |
| Development | Functional site in testing | EUR 12,000 | Testing and corrections list |
| Testing and adjustments | Corrections and optimizations | EUR 3,000 | Final validation |
| Deployment and training | Live site + user documentation | EUR 2,000 | Delivery acceptance report |
| Total | EUR 24,000 |
Built-In Flexibility Mechanisms
The change budget. In the contract, include a 10 to 15% budget of the total amount for minor changes requested during the project. For example, on a EUR 24,000 project, a EUR 3,000 budget absorbs reasonable adjustments without a change order. Beyond this budget, a change order is required.
Consumption alerts. Contractually define alert thresholds: at 50%, 75%, and 90% consumption of a phase's budget, the client receives a report with detailed hours consumed and remaining tasks. This mechanism prevents end-of-project surprises and creates shared accountability.
The re-estimation clause. At the end of each phase, the agency has the right to re-estimate subsequent phases based on learnings. If the mockup phase revealed greater complexity than anticipated, the development budget can be adjusted before committing.
Three-Model Comparison Table
| Criterion | Pure fixed price | Pure time & materials | Hybrid (milestone-based fixed price) |
|---|---|---|---|
| Client predictability | Maximum | Low | High (per phase) |
| Agency margin protection | Low if scope creep | Maximum | High |
| Scope flexibility | Low | Maximum | Moderate (adjustable per phase) |
| Sales complexity | Low | High | Moderate |
| Dispute risk | High (scope) | Moderate (hours) | Low (validated milestones) |
| Hours transparency | Not required | Essential | Strongly recommended |
| Suited for new clients | Yes | Difficult | Yes |
| Suited for long projects | Risky | Yes | Yes |
| Requires time tracking | Recommended | Mandatory | Mandatory |
Key figure: Agencies that practice milestone-based fixed price with time tracking report a client dispute rate 3 times lower than those using pure fixed price, and an average margin 8 points higher.
Decision Tree: Which Model for Which Situation
To help you choose, here's a decision tree based on the most common situations in web agencies.
The client gives you detailed specifications and a fixed budget? Go with milestone-based fixed price. The budget is fixed, but break it into phases to maintain checkpoints. Include a 10% change budget.
The client wants to "redesign their site" but doesn't know exactly what they want? Propose a fixed-price scoping phase (5-10 days) followed by time and materials support for execution. The scoping defines the scope; time and materials allows adjusting it along the way.
The client is an existing account who contacts you regularly for updates? Time and materials is the natural choice. You already have trust, the client knows your work pace, and requests are inherently unpredictable.
The client is comparing three quotes and wants a firm price? Fixed price is probably commercially unavoidable. But lock down your specifications, apply realistic margin coefficients, and include a clear change order clause for out-of-scope requests.
The project is innovative, with no equivalent in your history? Time and materials or milestone-based fixed price with re-estimation are the only responsible models. Signing a fixed price on a project whose complexity you don't master is playing Russian roulette with your margin.
Key takeaway: The choice of billing model shouldn't be an agency-wide policy ("we always do fixed price") but a project-by-project decision, based on scope definition, client maturity, and your track record on that type of work.
In Every Case, Time Tracking Is the Key
Whether it's fixed price, time and materials, or hybrid, one conclusion is clear: without time tracking, no model works properly.
With fixed price, without time tracking, you don't know if a project is overrunning until it's too late. You discover the overrun at delivery, when action is no longer possible. With real-time tracking, you detect the overrun at 50% of the project and can react: alert the client, trigger a change order, reallocate resources.
With time and materials, without time tracking, you can't justify your invoices. The client receives an amount they can't verify. Disputes are inevitable. With structured tracking, every invoice comes with a detailed, incontestable hours report that strengthens trust.
With the hybrid model, time tracking feeds consumption alerts, phase re-estimation, and client reporting. It's the technical foundation of the model.
Tracking Data Feeds Your Strategy
Beyond project management, time tracking gives you the data to optimize your billing model over the long term:
- Which billing model is most profitable for you? Compare the average margin of your fixed-price, time and materials, and hybrid projects. You might be surprised.
- Which types of clients are most profitable? Are trusting time and materials clients more profitable than fixed-price clients who negotiate every line?
- Which types of projects consistently overrun? If your e-commerce projects in fixed price overrun 80% of the time, that's a strong signal to switch to hybrid for that type of work.
Concrete example: A 15-person web agency analyzed 12 months of time tracking data. Result: pure fixed-price projects showed an average margin of 18%, compared to 32% for time and materials projects and 27% for hybrid projects. The agency decided to stop offering pure fixed price for projects over EUR 15,000. Within 6 months, its overall margin went from 21% to 28% -- that's EUR 52,500 in additional margin on EUR 750,000 in revenue.
The billing model is a strategic lever too often treated as an administrative detail. Take the time to analyze your data, test different models, and adapt your approach to each situation. The time tracking tools built for web agencies make this analysis possible. It's up to you to turn it into decisions.