Your 13-Week Cash Forecast is Wrong. That's Okay.
How Architecture and Engineering (A/E) firms can forecast when project schedules, WIP and client payments keep moving.
A 13-week cash forecast sounds straightforward.
List the money coming in. List the money going out. Look at the balance each week.
In an architecture or engineering firm, it is rarely that clean.
You might be expecting a $60,000 payment in four weeks, but that payment depends on reaching a certain project milestone. The milestone still needs client approval. Another $25,000 is sitting in WIP. A subconsultant wants to be paid next Friday, and payroll is not going to wait for any of it.
The firm can be profitable, busy and carrying a healthy backlog while still running into a cash squeeze.
That is why the goal of a 13-week forecast is not to predict the future perfectly.
It is to show you which incoming dollars you are depending on, what must happen before it arrives, and how much time you have to react if it does not.
What you will learn
In this article, we will look at how to use a 13-week cash forecast when project timing is uncertain, including:
how to separate expected cash from genuinely dependable cash;
how to treat WIP, milestones and client approvals;
how to identify the point where you need to act;
which assumptions are worth challenging every week; and
how to keep the weekly update to roughly 15-minutes once the system is working.
Forecast the process, not just the payment terms
One of the easiest mistakes to make is to forecast based on the invoice date and payment terms.
Invoice goes out. Terms are Net 30. Cash arrives 30 days later.
Except there may be several steps between the work and the cash.
For example:
Your 'Project Team' finishes milestone
→ principal reviews the work
→ client approves the milestone
→ invoice is issued
→ client's project manager approves it
→ invoice reaches accounts payable
→ payment is released
If your forecast says "$60,000 in Week 4," but the milestone is still waiting for client approval, Week 4 is really an assumption.
A better question is:
What still must happen before this money reaches the bank?
This helps you see the difference between a payment that is already moving through a known process and a payment that still depends on several things going right.
Stop treating all expected cash the same
You don’t need to assign complicated probability percentages to every invoice. A simple level of cash confidence is often enough.
We suggest to think about incoming cash in four categories.
Committed: The invoice is approved and you have a reasonably dependable payment date.
In process: The invoice has been issued, but it is still moving through the client's approval or payment process.
Dependent: You expect to bill it, but something still needs to happen first, such as milestone approval or completion of a project phase.
Not cash yet: Unbilled WIP, unsigned additional services or work tied to a future phase.
This matters because your obligations don’t have the same level of uncertainty.
Payroll has a date.
A tax payment has a date.
A consultant invoice may have a contractual due date.
A client milestone approval may not.
The practical rule is simple:
Do not fund a fixed obligation with an uncertain receipt without knowing your Plan B.
Work backwards from the $60,000
Let’s head back to our previous example.
You expect $60,000 from a client in four weeks.
Instead of asking whether that number is in the forecast, ask what is preventing it from being cash today.
If the answer is client approval, find out:
Who needs to approve it?
When is that expected?
Is anything outstanding from your team?
Does approval immediately trigger billing?
Once invoiced, how does this client normally pay?
If nobody can answer those questions clearly, the issue is not the spreadsheet. It is uncertainty in your billing process.
Now look at another $25,000 sitting in your WIP. Don’t automatically add it to your future cash allotment.
Ask yourself:
Is it contractually billable now?
Is it waiting for a PM or principal review?
Is part of it tied to a future milestone?
Are additional services included that have not been approved?
Could some of it legitimately be invoiced this week?
If $15,000 could be billed now but is waiting until the usual month-end review, you have identified an internal cash-flow bottleneck. This is something you can act on now.
Give every uncertain receipt a decision date
Most forecasts contain payment dates.
We suggest that you add another (equally important) date to your thinking:
When do we need enough confidence in this before we take another action?
Suppose payroll is $55,000 in Week 6 and the forecast assumes the $60,000 client payment arrives in Week 5.
If the payment is delayed, your projected cash balance drops below the level you are comfortable with.
Don’t wait until Week 5 to find that out. Your decision date might fit better in Week 3.
If the milestone is still not approved by then, this leaves you time to:
escalate the approval with the client;
invoice other WIP sooner;
follow up more actively on outstanding AR;
hold a discretionary purchase;
review your available line of credit;
reconsider the timing of a planned hire.
This is where forecasting earns its keep. It tells you when you need to make a decision, not just when you might run out of cash.
Challenge three assumptions every Friday
Once your 13-week forecast is established, you should not need to rebuild it every week.
Instead, challenge the assumptions most likely to change.
1. "The client will pay according to terms."
Ask: Where is the invoice currently sitting?
Has it been approved? Is AP waiting for something? Is it scheduled for the next payment run?
2. "We will bill that WIP next month."
Ask: Why not now?
Sometimes there is a good contractual reason. Sometimes it’s simply waiting for someone to complete an internal review. Those are two very different problems.
3. "That project phase starts in three weeks."
Ask: What must happen first?
Client authorization? Permit approval? Funding? Completion of another phase?
If upcoming payroll or hiring decisions depend on that work starting, those dependencies belong in the forecast.
Your 15-minute weekly update
Once your accounting and project information is organized, the weekly update remains simple.
Five minutes: What changed? Update payments received, invoices issued, project dates, consultant costs and any major expenses.
Five minutes: What is uncertain? Look at the top two or three receipts your firm is most dependent on.
Five minutes: What needs action? Find the lowest projected cash week. Has anything changed enough that you need to act now?
Then add another week to the end so your forecast always looks 13 weeks ahead.
The 15 minutes is not for rebuilding the spreadsheet.
It is for challenging what you believed last week.
Recap: forecast the uncertainty, not just the dollars
A useful 13-week cash forecast doesn’t need every number to be exactly right.
It simply needs to tell you:
which receipts your firm is relying on;
what has to happen before those receipts become cash;
which dependencies you control;
which payments cannot move; and
when you need to make a decision if something changes.
Your forecast does not need to predict the future.
It needs to give you enough warning to respond to it.
Make the forecast easier to trust
A 13-week forecast becomes much easier to maintain when WIP, invoicing, AR and project information are already being reviewed consistently.
If figuring out what is billable, what is outstanding and what is likely to be paid takes you an hour every Friday, the forecast probably isn’t the real problem. The workflow feeding it might be the real issue you face.
At Reach CPA, we help architecture and engineering firms build the accounting systems and routines behind that visibility, from WIP and invoicing reviews to cash-flow forecasting and ongoing financial reporting.
We can help you set up the process, then review the numbers with you so you can make decisions sooner, with a clearer picture of what is coming next.
Want better visibility into the next 13 weeks? Let’s talk.
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