Change Control Without Surprise Invoices
Scope changes during a build are normal. Surprises are not. Nothing reaches an invoice unless it was agreed, priced and scheduled in writing first, and overruns caused by our own estimation are ours to absorb, not yours to pay.
Every fixed-price project eventually meets a moment where something was not quite what either side assumed. How that moment is handled tells you more about a supplier than the proposal ever did. This article explains how we handle it, what we absorb ourselves, and what goes through written change control.
01. Two ways this usually goes wrong
Silent scope creep. The supplier absorbs small changes without discussion. The project quietly grows, and eventually quality or the timeline suffers without anyone having agreed to that trade-off.
Surprise invoicing. The supplier treats any deviation from the brief as billable, and the client learns a change was “extra” only when the invoice arrives, after the work is done and there is no leverage left.
Silent scope creep and surprise invoicing share one root cause: no agreed process for what happens when scope moves.
02. The rule: agreed, priced, scheduled, in writing, first
Changes of scope, delays on the client’s side and changes by third parties underneath the project all go through the same written process. Nothing reaches an invoice that was not agreed first, in writing, at a specific price.
| Step | What happens |
|---|---|
| 1. Raised | A change is identified by either side and described in writing |
| 2. Priced | Its cost is stated before anyone starts on it |
| 3. Scheduled | Its effect on the timeline is stated |
| 4. Agreed | Both sides accept it in writing |
| 5. Done and invoiced | Only now does the work begin, and only now can it appear on an invoice |
This sits inside the sequence described on how it works: the design is signed off before anything is built, and any change to it afterwards runs through the same process rather than being absorbed silently or billed retroactively.
03. What we absorb, and what goes through change control
Not every deviation is the client’s to pay for.
| Ours to absorb | Goes through change control |
|---|---|
| We underestimated the work | Scope that was not part of the original agreement |
| We misjudged complexity | Delays caused by the client’s own availability |
| We missed a requirement that was reasonably discoverable during the Diagnostic | A third-party system changing underneath the build in a way nobody could have planned for |
An overrun caused by our own estimation is ours to absorb. An overrun caused by a change is agreed first. That follows from measuring before quoting: if the measurement was done properly, an estimating error is the supplier’s responsibility.
The items on the right are real costs. They are not ours to absorb quietly, and they are not yours to discover after the fact.
04. How it fits with payment
Build engagements are invoiced in three parts: forty per cent at signing, thirty per cent at a milestone and thirty per cent at acceptance. The final payment falls due only once the acceptance criteria agreed at the Diagnostic are met.
A change reaches the invoice only as an agreed, priced item. It does not appear as an adjustment to the original three payments without having been agreed first.
05. Why this matters for margin, not only for trust
Unmanaged scope creep is one of the specific mechanisms behind margin eroding even as project volume grows: work expanding quietly beyond what was priced, on both sides of a supplier relationship. Written change control is not only a fairness mechanism between us and a client. It is the discipline that keeps a fixed-price engagement fixed, for both sides.
06. Four questions to ask any supplier
- Do you absorb overruns caused by your own estimation? If not, the fixed price is not fixed.
- Is every change priced before work starts on it? If not, the price arrives after the leverage has gone.
- Who agrees a change, and how is it recorded? If the answer is “we discuss it”, it is not recorded.
- Can I see what has been changed since the original scope? A list should exist at any point.
07. Frequently asked questions
What is change control?
A written process for what happens when scope needs to move. A change is described, priced and scheduled, and agreed in writing before the work is done.
Who pays when we underestimate the work?
We do. An overrun caused by our own estimation is ours to absorb.
What goes through change control?
Scope that was not part of the original agreement, delays caused by the client’s availability, and third-party systems changing underneath the build.
Can a change appear on the invoice without being agreed?
No. Nothing reaches an invoice that was not agreed first, in writing, at a specific price.
Does a change alter the acceptance criteria?
Only if the change says so in writing. The final payment still falls due only once the agreed acceptance criteria are met.
08. Next step
See the full payment structure and what triggers written change control. Pricing →
