What it means
A law firm records work as it is done but waits to invoice clients, so the unbilled balance ties up value and can delay cash collection. WIP days expresses that balance in equivalent days of billing activity under a chosen formula.
Link Academy describes WIP lock-up days, while LeanLaw discusses law-firm WIP reporting; these sources show professional-service conventions, and work-in-process inventory in manufacturing is a different use of WIP. Define what enters the WIP balance, such as recorded unbilled time, disbursements or other work under the accounting method, and do not treat every recorded hour as fully recoverable revenue because some work may be written down before billing or never charged to a client.
Choose an annual fee or billings figure consistent with the WIP valuation, since mixing gross standard rates with net realised fees can mislead. One illustrative method divides unbilled WIP by annual comparable fees and multiplies by 365, so if WIP is $1.2 million and annual fees are $9.7 million, the result is about 45 days.
A different period can use its number of days and matched fee flow, so document the conversion and any seasonal assumption before comparing periods. A period-end balance can be unusually high or low, so use average balances if the business cycle calls for it.
WIP days is distinct from debtor days, which measures billed amounts awaiting payment, and together they describe part of the cash lock-up from doing work to receiving money. A low WIP-days figure can reflect timely billing but may also come from writing off work, so check both.
A high figure can reflect delayed billing, long projects, client approval cycles or work that has not been scoped clearly. Inspect aged WIP by matter, client and responsible professional, because a single average can hide a few old balances that need specific decisions.
Agree billing milestones before work begins where possible, since waiting for project completion may be unnecessary under the contract. Review draft invoices promptly, ensure time entries are accurate and understandable, and record the decision, owner and next step when a partner holds an invoice because of a dispute or a strategic reason.
Do not bill unfinished work in breach of the engagement terms merely to improve a ratio, and check client funds and retainers separately under applicable professional rules because unbilled work is not the same as cash held on account. Revenue recognition can differ from billing, so the dashboard should state the accounting perspective it uses.
A growth period may lift WIP even with stable billing practices, and a sudden reduction in annual fee run rate can raise WIP days mechanically even if the balance did not change. For fixed-fee projects, recorded effort and billable milestones may diverge, so use contract-specific analysis, track write-offs, invoice disputes and collection after billing, segment practices with different matter lengths, and assign owners to aged items so that the report leads to decisions.
In practice
Real-world examples.
Example
A fictional law firm has unbilled WIP of $1,200,000 against annual fees of $9,700,000. Dividing and multiplying by 365 gives about 45 days. The finance director records the balance date and fee basis so that next quarter's figure is comparable.
Example
A fictional consulting firm separates WIP days from debtor days when reviewing cash lock-up. WIP days shows how long finished work waits before an invoice goes out, while debtor days shows how long issued invoices wait for payment. Together they show where cash is stuck.
Example
A fictional partner reviews old unbilled matters and records why each has not yet been invoiced. One awaits client approval and another is a fixed-fee milestone not yet reached. Each gets an owner and a next step.
Formula
Calculation
WIP days = defined unbilled WIP balance / comparable annual fee flow x 365. State the balance date, valuation, fee basis and period.
Worked example with assumed figures. A firm has unbilled WIP of $1,200,000 at year end and comparable annual fees of $9,700,000. WIP days = $1,200,000 / $9,700,000 x 365 = 0.1237 x 365 = 45.2 days, so about 45 days.
If the firm bills a $300,000 batch of invoices, WIP falls to $900,000 and WIP days becomes $900,000 / $9,700,000 x 365 = about 34 days. If instead annual fees fall to $8,000,000 with WIP unchanged at $1,200,000, WIP days rises to $1,200,000 / $8,000,000 x 365 = 54.75, about 55 days, purely because of the lower fee run rate.Case study
Seen in the real world.
In this fictional case, Birch Legal found invoices delayed in internal review. It assigned draft-bill owners and watched aged WIP, write-offs and collections rather than the single ratio alone. The case is invented and makes no real accounting claim.
In the invented numbers, Birch's WIP fell from $1,200,000 to $900,000 after three months of faster review, taking WIP days from about 45 to about 34 on unchanged annual fees of $9,700,000. The finance team also checked that write-offs did not rise, so the improvement came from faster billing rather than hidden discounts. Birch used the metric to find avoidable delays while keeping invoices accurate, fair and within the agreed client terms.
Watch out
Common mistakes.
- Confusing unbilled WIP with unpaid invoices.
- Mixing WIP at standard rates with net fees without explanation.
- Reducing the figure by premature billing or hidden write-offs.
Questions
People also ask.
Is WIP days the age of every entry?
No. It is often a balance-to-fee-flow proxy; inspect aging for specific items.
Does a lower figure guarantee faster cash?
No. Billed invoices can still wait for collection.
What should be reviewed with it?
Aged WIP, billing delays, write-offs and debtor days.
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