WIP and Unbilled Work: How to Turn 'Work Done' into 'Cash Collected'

A firm can be busy and still feel short on cash.

That sounds backwards, but it happens all the time in architecture, engineering, construction, and interior design firms. The team is working. Projects are moving. Clients are asking questions, reviewing drawings, requesting changes, attending meetings, and getting real value from your people.

Then the monthly overhead piles up—payroll comes around, software renewals hit, consultant invoices arrive. Rent, insurance, and subscriptions all keep doing what they do best: showing up on schedule.

But the cash from the work your team has already done? That may still be sitting somewhere between “we did the work” and “the client paid the invoice.”

That gap is where WIP (work-in-progress) and unbilled work create stress. To be clear, this is not usually because firm owners are ignoring their numbers. More often, it happens because everyone is focused on getting the work done. The project moves forward, the billing conversation gets pushed to later, and then “later” becomes next month.

Or the month after that.

Work completed is not the same as cash collected

A lot of owners mentally count revenue when the work is done.

That makes sense. Your team spent the time. The client received the benefit. The project advanced. In your mind, the firm has earned that money.

But from a cash flow perspective, there are three separate steps:

Work completed → invoiced → collected

The problem is that many firms have a loose process between those steps.

Work gets completed, but nobody has reviewed whether it is ready to bill. Or the invoice is waiting on missing timesheets. Or the project manager has not approved the draft. Or the contract says the firm can’t bill until the next milestone, even though the team has already carried two months of costs.

We often see firms finish a meaningful portion of a design phase before anyone checks what is actually billable. The owner knows the team has been busy, but the invoice does not reflect that effort yet.

This is when cash starts to feel tighter than it should be.

Billing is not just an accounting task. In a project-based firm, billing is an integral part of project management.

WIP and unbilled work, without the accounting fog

Depending on your accounting setup, WIP can have a more technical meaning, but most owners can start with a simpler definition:

WIP or unbilled work is effort already spent that has not hit an invoice yet.

That effort might be staff time, consultant costs, reimbursable expenses, approved extras, or work completed under a fixed-fee agreement that has not reached the next billing point.

It can also include the sneaky stuff: the second round of options that was not in the original agreement, the extra coordination meeting, the revised layout direction, the site issue that turned into three more calls, or the “quick” client request that was not quick at all.

Remember, not all WIP is immediately billable. The contract you have detailing when and how you bill matters. That is the key.

If your team has spent time or incurred costs, someone should track where that value sits. Is it billable now? Is it waiting on a milestone? Is it outside scope? Is it going to be written off? Is it something you need to discuss with the client?

When nobody reviews it, WIP becomes stale. Outdated or old WIP is harder to bill. This is not because the work was not real, but because the conversation gets colder the longer you wait. The details can often get lost in all the other conversations or decisions that where made since then with the client.

Your billing method matters more than most owners think

The billing structure in the contract can either support cash flow or put pressure on it.

There is no single billing method that works for every firm or every project. It depends on the contract, the industry, the client, the type of work, and how predictable the project is. But there are a few patterns worth watching.

1. Fixed fee billing

Fixed fee pricing is common on larger projects and government work. It can work well when the firm has a solid project budget, understands the scope, and can manage the work efficiently.

The upside is that if the team performs well and keeps costs under control, the firm may protect or improve its profit.

The risk is that fixed fee work can hide problems until later. If the scope expands, hours run over, or billing is delayed, the firm may not feel the issue right away. But the costs are still there.

Fixed fee billing usually shows up in one of two ways: percentage complete or designated milestones.

Fixed fee billed by percentage complete

Percentage complete billing is often a better fit for firms that are well budgeted and have a reasonably predictable project path.

Instead of waiting for one major milestone, the firm bills based on progress. If the project is 40% complete, the billing can reflect that progress, assuming the contract allows it.

This can be good for cash flow because billing follows the work more closely.

But it only works if the firm has a meaningful way to measure progress. Guessing at percentage complete every few months is not much of a system.

A better routine is to set the project budget at the start, define the major phases, review progress monthly, and compare actual time and costs against what has been billed.

The question is not just, “How much have we invoiced? ”

It is also, “Does the invoice match the work we have actually completed? ”

Fixed fee billed by designated milestones

Designated milestone billing can look clean in a proposal. The firm bills when a specific phase or deliverable is complete.

The issue is that the work and the billing often times are too far apart.

We often see firms get two or three months into a project before they can invoice under the milestone structure. By that point, staff have been paid, consultants may have submitted invoices, and the firm has absorbed a large amount of cost before cash has come back in.

This setup can turn the firm into the project’s bank.

This does not mean milestone billing is always wrong. Some clients expect it. Some contracts require it. But owners should be careful with long gaps between billing points.

Before agreeing to milestone billing, ask:

• How much work happens before the first invoice?

• How much payroll will we carry before that milestone?

• Are consultant costs due before we are paid?

• Can we use smaller milestones?

• Can we include an upfront retainer?

• Would monthly progress billing be more suitable instead?

A billing structure can be simple without forcing the firm to fund months of work upfront.

2. Monthly time and materials

Monthly cost in time and materials is essentially hourly billing with a monthly rhythm.

Your costs come in, and the invoice goes out.

This can work well when the scope is likely to shift, the client needs ongoing support, or the project is less predictable. The benefit is that billing follows actual effort more closely.

The main catch is that time and materials billing depends on clean time records. Another catch is that this method allows little room for capturing more efficiencies – your bill-out rates multiplied by time, make sure the bill-out rate is adequate to provide your desired profit.

If timesheets are late, vague, or reconstructed from memory, the invoice gets weaker. The client may have more questions. The project manager may need to clean things up. Meanwhile, the admin person waits and billing slips.

For this method to work, timesheets need to be completed weekly at least, project codes need to be used consistently, and unusual time should be reviewed before the invoice is drafted.

Timely timesheets are what keep billing moving forward.

Where retainers help

A retainer can be especially useful when the firm is billing monthly.

The practical benefit is simple: it helps cover wages and early project costs before the first full invoice is issued and paid.

Without a retainer, the firm may start work, pay staff, wait until month-end, send the invoice, and then wait again for payment. That can easily create a cash gap at the beginning of the project.

With a retainer, the firm has some cash upfront to support the early work.

We often see owners hesitate to ask for a retainer because they worry it will feel awkward. But when it is explained clearly, it usually sounds reasonable:

“This allows us to reserve project capacity and begin the work properly.”

That is not pushy. It is practical.

The retainer should be clearly defined in the contract. Spell out whether it is applied to the first invoice, held for the final invoice, replenished, refundable, or non-refundable depending on the agreement and local requirements.

A retainer will not fix poor billing habits, but it can stop the firm from carrying all the early costs alone.

How unbilled work quietly builds up

Unbilled work rarely appears in one dramatic moment. It builds through normal project friction.

One common cause is waiting for perfect timesheets. The invoice is ready except for three missing entries, or a project manager needs to confirm whether certain hours are billable. Everyone is busy, so the invoice waits.

Another cause is milestone timing. The team keeps working, but the contract does not allow billing until the next deliverable is complete.

Scope creep is another big one.

The client asks for one more option. A meeting creates extra follow-up. A site condition changes the plan. A consultant needs additional coordination. The team wants to be helpful, so they keep moving.

That instinct is good for client service. The problem is when the extra work is never documented, approved, or billed.

Being generous is different from being unclear.

This simple internal rule can help: when a client request changes to the scope, timeline, deliverable, or level of effort, it gets flagged before the work continues.

It does not need to become a confrontation. It just needs to become visible.

A simple monthly WIP routine

A monthly WIP routine does not need to be complicated. For many firms, it can be a focused review with the owner, project managers, and whoever handles invoicing.

The goal is to answer four questions:

WHAT WORK HAS BEEN DONE? WHAT CAN BE BILLED? WHAT NEEDS APPROVAL? WHAT SHOULD NOT CARRY INTO NEXT MONTH?

Each month, review unbilled time by project. Look for old hours, missing time, incorrect coding, and possible additional services.

Review unbilled expenses and consultant costs. Make sure reimbursables are captured and costs are not sitting in the accounting system without being passed through where appropriate.

For fixed fee projects, review progress. If the project is billed by percentage complete, does the invoice reflect the actual work completed? If it is milestone-based, how much cost is the firm carrying before the next billing point?

Then review scope changes. What changed this month? Was it approved? Has it been billed? Does the client know it is outside the original agreement?

Finally, look at old WIP. Anything sitting too long needs a decision. Bill it, write it off, clarify it, or fix the process that allowed it to sit there.

Old WIP should not live in limbo.

Who owns the process?

WIP review needs clear ownership. If everyone owns it, no one owns it.

The owner should stay close to large unbilled balances, projects creating cash pressure, write-offs, and contract structures that repeatedly cause billing delays.

The project manager should confirm the project story. Is the work in scope? Is the percentage complete reasonable? Was the extra work approved? Does the invoice match what work was done?

The admin or accounting person should prepare the reports, draft invoices, missing timesheet list, unbilled expenses, and questions that need review.

Accounting can prepare the numbers, but they may not know the project story. That is why project manager input matters.

Use your systems to see the gap

Your system does not need to be fancy. It just needs to show what has been done, what has been billed, and what is still waiting.

Some firms track time and project activity in a project management tool, then invoice through an accounting system like Xero or something similar. That can work well, as long as the information is reviewed regularly.

The goal is not just to send invoices. The goal is to spot timing gaps.

At any point, you should be able to answer:

• Which projects have unbilled time?

• Which invoices are still in draft?

• Which clients are overdue?

• Which costs have not been passed through?

• Which additional services were approved but not billed?

• Which projects are carrying costs before the next billing point?

A simple system that gets reviewed monthly is better than a complicated system nobody trusts.

Scripts for the awkward moments

A lot of unbilled work stays unbilled because people want to avoid uncomfortable client conversations. A few simple phrases can help you navigate these moments.

When a client request is outside scope:

“We can absolutely help with that. Based on the original scope, this would be treated as an additional service. We’ll outline the added work and fee before moving forward so there are no surprises.”

When the team needs approval before continuing:

“Before we spend more time on this, we want to confirm the scope and fee with you. That way we can keep the project moving without creating confusion later.”

When the project is approaching the budget:

“We are getting close to the current project budget based on the work completed and remaining items. Let’s review the next steps so we can confirm priorities before additional time is incurred.”

These conversations are much easier before the work is done than after the invoice is overdue.

A practical checklist

Weekly:

• Timesheets completed by a set deadline

• Project managers review time for accuracy

• Out-of-scope requests are flagged

• Client approvals are documented

• Project notes are updated while the work is fresh

Monthly:

• Review unbilled time

• Review unbilled expenses

• Review fixed fee progress

• Review milestone billing gaps

• Review additional services

• Send invoices on a consistent schedule

• Follow up on overdue invoices

• Decide what to do with old WIP

Before signing a new contract:

• Confirm the billing method

• Avoid long gaps between billing points where possible

• Consider a retainer

• Define additional services clearly

• Clarify reimbursable expenses

• Make sure the billing structure supports payroll timing

Key takeaways

Most firms do not end up with unbilled work because they are careless. It usually happens when the team is busy serving clients and keeping projects moving.

But completed work should not sit unnoticed.

The fix is not to become aggressive with clients. The fix is centered on being more consistent internally.

Having clear billing structures, sensible time tracking, monthly WIP reviews, and simple scope conversations can make cash flow feel much less unpredictable.

This month, pick your five most active projects and ask:

What work has been done, what has been billed, and what is still sitting unbilled?

That one review can tell you a lot about where cash is getting stuck.