How AI can speed up WIP reviews and billing in accountancy firms

The median firm in NatWest’s 2024 Accountancy Benchmarking Report, a survey of 23 UK accountancy firms, took 105 days to turn recorded time into cash. Part of that wait is clients paying slowly. The rest is work the firm has done and not yet billed, and that part is in the firm’s own hands.

Most firms already have the report that would shorten it. The aged WIP report sits in the practice management system every week. What is missing is the time to go through it properly.

That is a job AI and automation are well suited to. This post covers why WIP reviews slip, what a day of lock-up costs and where AI helps. It also sets out where a person still has to decide and three ways to do it with Copilot inside Microsoft 365.

WIP, debtors and lock-up in plain terms

Lock-up is the time between doing the work and banking the fee. It has two halves:

• WIP days: time recorded on a job that has not been billed yet.
• Debtor days: bills raised that have not been paid yet.

Add the two and you have lock-up. The sum is (WIP + debtors) ÷ annual fees × 365.

The split matters because the two halves have different owners. When a client pays is partly up to the client. When you raise the bill is up to you.

The same survey shows how far WIP days can drift. Large firms’ WIP days rose from 33 to 41 between its last two surveys, while small firms cut theirs from 32 to 26. That is a 15 day gap in how long recorded time waits for a bill, before credit control has even started.

Why WIP reviews slip

WIP reviews slip because of how the job is done, not because the data is missing. Five things get in the way:

• The report is long and most of it needs no action. A manager scrolls through every client to find the dozen that matter.
• The decision needs context. A balance alone is not enough. The manager also has to check when the client was last billed, how the balance has moved and whether the job is finished.
• It is nobody’s urgent job. Client deadlines win, so the review happens monthly if at all.
• Old WIP is harder to bill. The longer time sits, the further the client has moved on and the more a fee note turns into a negotiation. Writing it off becomes the easy option.
• Partners cannot see who has acted. A decision made in someone’s head, or in an email to the billing team, leaves no trail.

None of these is a software problem. The friction is in the reading, the sorting and the following up, and that is exactly the kind of work that can be taken off people. It is the same pattern behind the five admin jobs an agent can take off an accountancy firm: the data exists, and nobody has time to read it.

What a day of lock-up costs

Each day of lock-up ties up one day of fee income: annual fees ÷ 365. For a £3m firm that is about £8,200 a day, so the 105 day median means roughly £863,000 earned and not yet in the bank.

Be honest with yourself about what that figure is. It is one-off working capital, not extra income. The same fees arrive sooner, which means less partner capital or overdraft funding the gap.

There are two further gains that are harder to put a number on. Bills raised while the work is fresh are easier for clients to accept. And the review itself takes manager time. For a firm with 12 managers, a half-hour review once a month is 72 hours a year. Done weekly, as it should be, it would be over 300, which is why it rarely happens weekly.

Where AI helps and where it does not

Most of a WIP review is rules and routing, and only a small part of it needs AI. Knowing which is which is what keeps the result accurate enough for an accountant to trust.

Firms are looking for places to put AI to work. In ICAEW’s 2026 research into mid-tier firms, 86% have a technology strategy that includes AI, yet most describe their use so far as moderate. That matches what we see in how accountancy firms actually use Copilot in-house. WIP is a sensible early candidate: the data is internal, the rules are your own and the result shows up in a number you already track.

The pattern is simple. Software does the reading and sorting. AI handles the questions and the wording. People keep every decision that touches a client or a fee.

Three ways to do it inside Microsoft 365

There are three levels, and the first costs nothing beyond a Copilot licence. Start at the lowest one that solves your problem.

1. By hand with Copilot

Export the WIP report to Excel or CSV, give the file to Microsoft 365 Copilot and ask a plain question:

List every client with WIP over £2,000 and no bill in the last 60 days. Group them by manager, largest balance first.

Copilot can analyse a spreadsheet you attach and return the list in seconds. Our guide to Copilot in Excel covers what it can and cannot do with a sheet. It is a good test of whether your thresholds are right before you build anything.

The limits are practical ones. Someone has to remember to do it, nothing is logged and nobody is chased. Check the totals against the report the first few times, and only use a Copilot your firm has approved for client data. If that approval has not happened yet, using Copilot with client data sets out what to check.

2. In your practice management software

Most practice systems can schedule a saved WIP report, and some have dashboards or alerts on top. Check what yours already does before you pay for anything new.

The usual gap is the last step. The report still has to be opened and read, and the decision still happens in an email or a conversation that nobody can see afterwards.

3. An agent built in Copilot Studio

An agent removes the remembering. It picks up the report when it arrives, applies your rules, puts each manager’s exceptions in front of them in Teams and records what they decide.

The routine steps run as ordinary Power Automate flows, and Copilot Studio adds the chat on top so people can ask questions of the same data. Our guide to Copilot Studio vs Power Automate explains where each one fits.

This level costs money to build and to run. Our breakdown of what an agent build costs a 30-person firm in year one sets out the budget lines, and our pricing page has the fixed prices.

What a WIP agent looks like in practice

Here is the flow we use in our own WIP and billing agent, as one worked example of level three:

1. The practice system’s scheduled WIP report is emailed to a shared mailbox and filed, or dropped straight into the folder.
2. The columns are mapped, so the same fields are read every week.
3. Your thresholds, ageing bands and week-on-week movement are applied, and the exceptions are grouped by manager.
4. On Monday morning each manager gets a card in Teams listing only their clients, with last bill dates.
5. The manager chooses bill now, defer or write off for each client and submits.
6. A fee request goes to the billing team for every “bill now”, including the manager’s own note, and every decision is logged.
7. On Friday partners get a summary of the decisions taken and any clients nobody has actioned.
8. Managers can ask “what should I be billing now?” in Teams and get an answer from the latest week’s data, with the week it covers stated.

Two design choices matter more than the technology. The agent never raises a bill, so a person approves everything that reaches a client. And every decision leaves a record, so a deferral in March can be explained in June.

If your firm already has a written WIP review procedure, that document is most of the specification. From SOP to agent shows how a written process turns into steps an agent can run.

The agent page has a short demo and a calculator you can put your own numbers into.

What you need in place first

The technology is the easy part. These five things decide whether any of the three levels works:

• Time recorded promptly. Nothing can flag WIP that is not on the system yet.
• A fixed saved report. Excel or CSV, same columns every week, so nothing breaks when someone tweaks a layout.
• Agreed thresholds and ageing bands. What balance counts as over, and how long without a bill is too long. These are partner decisions, not technical ones.
• A clear owner for every client. If nobody knows which manager owns a client, nobody gets the prompt.
• A named owner for the process. One person who checks it is still running and still right. We cover this in why every agent needs an owner, and how to know your agent still works covers the checking.

If client data is involved, also settle where it goes. An agent built in your own Microsoft 365 keeps the data inside the tenant you already govern. Our post on whether Copilot agents are secure goes through the detail.

What AI will not fix

Faster WIP reviews shorten one half of lock-up and leave four problems untouched:

• Debtor days. Billing sooner does not make clients pay sooner. In NatWest’s survey small firms’ debtor days rose from 55 to 66, which is a credit control problem.
• Late or missing timesheets. If time goes on a week late, the review is a week behind before it starts.
• Pricing and scope. If a job is over because it was underquoted, flagging it sooner shows the problem sooner. It does not cure it.
• People who do not act. A prompt nobody answers is still unbilled WIP. Partner visibility helps, but it only works if partners look.

Fixed fee and monthly billed clients also need separate treatment. Their WIP balance means something different, so they need their own thresholds or should be left out of the review altogether.

Where to start this month

If you already have Copilot, you can test the idea in four weeks without buying anything:

1. Work out your lock-up and split it into WIP days and debtor days. If WIP days are the larger problem, carry on.
2. Agree one threshold and one period with the partners, for example over £2,000 and no bill in 60 days.
3. Run the review by hand with Copilot every Monday for a month, on one team.
4. Time it. Note how long the review takes now, how many clients were flagged and how many were billed as a result.
5. If it works but depends on someone remembering, that is the point to automate it.

If you get to step five and want to see what the automated version looks like, the WIP and billing agent page has a short demo, and it is one of six agents we build for accountancy firms. A free 30-minute call is enough to check whether your practice system can feed it. If you would rather the practice manager built the first version, Copilot and agent training for accountancy firms builds its exercises from your practice’s own work, and this WIP export is a good job to bring.

Sources checked

Last checked: 2 October 2026.

• NatWest, The accountancy trends shaping 2024: summary of the NatWest Accountancy Benchmarking Report 2024, a survey of 23 firms across England, Scotland and Wales. Source of the lock-up, WIP day and debtor day figures.
• ICAEW, Mid-tier firms focused on AI and consolidation, 22 May 2026: source of the 86% figure and the description of AI use as moderate.
• Microsoft 365 Copilot release notes: Copilot’s ability to analyse spreadsheet and CSV files.
• FiveForward WIP and billing agent: the worked example and the cash released formula.

If you want to know whether your practice system can feed a WIP agent, book a free 30-minute call. No pitch, just a straight conversation about what would work for your firm.