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Cash vs. Accrual vs. Work in Progress Accounting: Which is Best for AEC Firms?

Evelyn March
Group Director
BST Global

Cash basis and accrual basis are two different methods of accounting. Each method tells a different story about revenue, but neither method gives the whole story – that's where the work in progress (WIP) method comes in.

It’s an important question: which accounting method is most effective at providing insight into your firm’s revenue? Some say accrual basis accounting is more effective than cash basis accounting.

But many times, if architecture, engineering, and environmental consulting (AEC) firms only leverage accrual basis accounting, they miss out on an even deeper level of insight of revenue that can only be achieved with the accrual based WIP method.

While each method provides a snapshot of your AEC firm’s income, the WIP method provides the most accurate representation. The impact of this? Your team is able to get a clearer picture of your firm’s revenue journey.

Before we dive into how WIP gives the level of revenue insight your AEC firms needs to be successful, let’s review the more commonly used cash and accrual basis accounting methods first.

Cash Basis Accounting

The end goal of any profitable business is to monitor cash flow. That’s why for the cash basis method of accounting, income is booked when money is received, and expenses are booked when money is paid. In other words, items are booked when money changes hands. While this makes the value of your firm’s revenue extremely accurate, it can also paint a misleading picture.

If a large sum of revenue is received and recorded before bills are paid, your firm may falsely appear more profitable, as assets will be greater than liabilities. Of course, the reverse is also true. If a firm pays for expenses prior to receiving the money and recording this revenue, it can make a company look like it’s headed in the wrong direction. In this case, your balance sheet would show the value of your firm’s liabilities as greater than the value of its assets.

Accrual Basis Accounting

While cash basis accounting records the actual movement of cash, accrual basis allows for the prediction of revenue. With this method, if an invoice is received for completed services (expenses), or a bill is submitted to a customer (revenue), both are booked at that point to predict future revenue and expenses. So, while items are booked when money changes hands with cash basis, items are booked when an invoice passes hands with accrual basis.

This prediction allows you to see the cash flow that’s already in motion once an invoice is sent – but what if you could predict revenue even before invoices are sent to the client? That would be the holy grail of data analysis. And yes, it’s possible… if your enterprise resource planning (ERP) software can calculate WIP.

Work in Progress

What is WIP? Accrual-based WIP is the value of work completed, but not yet billed. Since there are parameters that determine the contractual amount that you can bill, what if you used those parameters to figure out the value of work before you billed it?

This additional layer of accrual allows you to book the revenue that comes from work completed in the month it occurred. By booking revenue at this point in time, it provides the truest picture of your firm’s forecasted income. Let’s explore this concept a little further.

Since the accrual method means you book expenses when your firm receives an invoice or timesheet, you have a clear picture of your cost for a given month. No matter which accrual method you choose (accrual basis or accrual-based WIP), your expenses will always be booked in the month it occurred – this will not change. But with WIP, you have an additional option for booking revenue: your AEC firm can now book revenue in the month work was completed.

We know it takes money to make money, so booking your revenue in the same month that you booked your expenses gives the truest picture of your firm’s financial standing. But by taking it a step further with the WIP method, the WIP value on your financial reports will show the value of work before you bill it in the future.

So, how is this added benefit helpful to your AEC firm? We’ll take a look at that next.

The Revenue Story with WIP

In a scenario where WIP is not used, and expenses are booked in a given month yet billed months later, your picture of expenses versus revenue is skewed. The month of the expenses would appear with no offset of revenue, and when the invoice is sent, the revenue would appear with no offset of expenses. Because these values were booked in two separate time periods, it would be challenging to make the connection of how much expense it took to earn the amount invoiced.

On the other hand, if the WIP method were used, you would accurately depict the revenue earned in the same month the expenses were booked. Seeing that this value was booked as WIP, it alerts you that this is your future billing amount.

Are you starting to see the extra layer of analysis your firm would receive?

Because WIP is a statement of what you expect to bill in the future, when an invoice is sent, that value is offset from the WIP account. By booking that value in WIP, you are now able to evaluate how long it took from completing the work to billing it. That same principle applies when cash is received. Noting the date of the invoice, and the date that cash was received, it shows how long it took for a client to make a payment. Thus, WIP gives you a complete timeline from work completed to billing, and then from billing to cash collected.

Here’s another way to look at it: Say your team completed work in January. According to the WIP method, you would book that work in January. Then, if you were to review your firm’s WIP balance (reminder: this is work you’ve completed, but are waiting to bill) in March and saw there was a balance for WIP that was booked in January, this would immediately alert you that the work completed in January had not been invoiced yet as of March.

Your firm can now proactively review WIP and give attention to projects that have fallen behind in invoicing, thus, having a positive impact on your firm’s cash flow.


While your AEC firm can choose to use any of the three accounting methods, it’s important to understand the added benefit of WIP in its ability to enable your firm to proactively analyze and maximize its profits.

By incorporating WIP into your accounting practices, it opens communication between your Finance and Project Management team to discuss the time lapse between work completed and work billed. Opening this dialogue allows the project team to join in the ownership of a healthy cash flow and also aids in the dialogue with your clients as you manage the time from billing to payment.

Want to learn other important AEC industry terms? We’ve created a glossary packed with 150 terms that covers the entire project lifecycle, all in the context of an ERP solution. Get your own free copy of The Ultimate ERP Glossary for AEC Firms by using the link below!


Evelyn March Evelyn March is BST Global’s Group Director of Training and Development. Evelyn joined BST Global in 2006 as a Support Director, ensuring the satisfaction of the BST global client base. Combining the honed skills gained from her industry knowledge and coupling it with assessed internal needs to support client satisfaction, she began to develop learning criteria for internal staffing. The success of the training criteria has led to a successful on-boarding and ongoing training and development department.

Evelyn March

Group Director

BST Global


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