Lock-up: diagnosing the cash disease of WIP and debtor days

A firm books $30m in fees, posts a healthy profit margin, and still cannot fund partner drawings in March. Why? Because $9m of that "profit" is trapped: unbilled hours sitting in the system and invoices the clients have not paid. The partners are rich on paper and broke in the bank.

This is lock-up, and it is the most common cash disease in a law firm. Let us learn to diagnose it.

What lock-up actually is

Lock-up is the total value of work you have done but not yet turned into cash. It has two parts:

• WIP (Work in Progress): time recorded by fee earners but not yet billed to the client. You did the work; you have not sent the invoice.
• Debtors (accounts receivable): invoices you have sent but the client has not paid.

Cash flows in a simple chain:

Do the work → WIP → send invoice → Debtors → client pays → Cash

Every day work sits in WIP or debtors is a day your money funds someone else's balance sheet. Law firms are especially exposed because most are partnerships funded by partner capital, not big equity buffers. Trapped cash means the partners' own money is stuck.

Measuring the disease: lock-up days

You measure lock-up in days, not dollars, so firms of different sizes can compare.

The core idea: how many days of revenue are sitting locked up?

Total lock-up days = (WIP + Debtors) / Annual fees x 365

Take our firm:

• Annual fees: $30m
• WIP: $5m
• Debtors: $4m
• Total lock-up: $9m

Lock-up days = (9,000,000 / 30,000,000) x 365 = 109.5 days

So the firm carries roughly 110 days of fees in limbo. Industry surveys of mid-sized firms often cite lock-up in the 100 to 150 day range, though this varies widely by practice area. (Treat any benchmark as an estimate, not a rule.)

Split it: WIP days vs debtor days

The total number hides the real problem. Always split it, because the fixes are different.

WIP days = WIP / Annual fees x 365

= 5,000,000 / 30,000,000 x 365 = 60.8 days

Debtor days = Debtors / Annual fees x 365

= 4,000,000 / 30,000,000 x 365 = 48.7 days

Now you know something useful. The firm's biggest problem is WIP: fee earners are working but not billing. Debtors is a smaller (though still real) issue.

A quick note on precision: some finance teams calculate debtor days on billed revenue including VAT, and WIP days on fees excluding VAT. Be consistent, and know which base your denominator uses. What matters most is tracking the same number over time.

Why WIP and debtors get stuck (the real causes)

Numbers point you to the disease. Behavior explains it.

WIP gets stuck because:

• Partners "sit" on time before billing, waiting for the "right moment" or a natural milestone.
• Fees are not agreed up front, so billing feels like a negotiation.
• Time is recorded late, so the matter is never ready to bill.
• Long matters (litigation, big transactions) with no interim billing.

Debtors get stuck because:

• Invoices are vague, so clients query them and delay.
• No one owns collection; it is "the finance team's job" but partners hold the relationship.
• Generous or undefined payment terms.
• The client is unhappy with the service and the unpaid bill is really a dispute.

The pattern: WIP is usually a partner discipline problem. Debtors is usually a process and relationship problem.

Modelling the cash you can release

Here is where finance earns its seat. You can put a dollar figure on improvement, which is far more persuasive to partners than a lecture about discipline.

The cash released by cutting one day of lock-up:

Cash per day = Annual fees / 365

= 30,000,000 / 365 = $82,192 per day

That single number changes conversations. Every day you strip out of lock-up puts about $82,000 back in the bank.

Scenario: cutting WIP days

Suppose the firm gets WIP days from 60.8 down to 45 (still not aggressive). That is a 15.8 day reduction.

Cash released = 15.8 x 82,192 = about $1.3m

Scenario: cutting debtor days

Suppose debtors improve from 48.7 to 40 days, a 8.7 day reduction.

Cash released = 8.7 x 82,192 = about $715,000

Combined

Together that is roughly $2m of cash freed, without winning a single new client. The work is already done. You are just collecting faster on what you already earned.

That $2m can fund partner drawings, repay the firm's overdraft, or reduce the capital each partner has tied up in the business.

Here is a compact way to model it in a spreadsheet or notebook:

annual_fees = 30_000_000
wip = 5_000_000
debtors = 4_000_000

cash_per_day = annual_fees / 365

wip_days = wip / annual_fees * 365
debtor_days = debtors / annual_fees * 365

# target reductions
wip_reduction_days = wip_days - 45
debtor_reduction_days = debtor_days - 40

cash_released = (wip_reduction_days + debtor_reduction_days) * cash_per_day
print(round(cash_released))   # ~2,053,000

The logic matters more than the code: days saved x cash per day = cash released.

Turning the diagnosis into action

A finance lead does not just report lock-up. They break it down by owner and by matter.

• Rank partners by their WIP days. The average hides the offenders. One partner sitting on 200 days of WIP can distort the whole firm.
• Age the debtors. Split into 0 to 30, 31 to 60, 61 to 90, and 90+ days. Cash risk lives in the 90+ bucket, where some debt may never be collected.
• Set interim billing on any matter running longer than, say, a month. Bill monthly rather than at the end.
• Agree fees and payment terms up front, so billing is administrative, not a fight.
• Make partners own collection of their own clients, with finance providing the data and chasing support.

For a solid primer on the finance mechanics behind receivables and cash conversion, the Corporate Finance Institute's guide to the cash conversion cycle is a clear, free resource. Lock-up is essentially the law firm version of the same idea.

Watch the traps

A few things trip up people new to lock-up.

Do not confuse profit with cash. Our firm is profitable and cash poor at the same time. Both statements are true. Lock-up is precisely the bridge between them.

Do not write off WIP quietly to "clean up." Writing off unbilled time makes lock-up days fall, but it destroys real value. Distinguish between collecting faster (good) and giving up on fees (a loss). Track write-offs separately.

Do not chase debtors so hard you damage relationships. The goal is disciplined, predictable billing that clients understand, not aggressive dunning that costs you the client.

Beware seasonality. Lock-up days spike around big matter completions or quarter ends. Compare like periods and watch the trend, not a single snapshot.

Key Takeaways

• Lock-up = WIP + debtors, measured in days: (WIP + Debtors) / Annual fees x 365. It is the cash trapped between doing the work and getting paid.
• Always split WIP days from debtor days. WIP problems are usually partner billing discipline; debtor problems are usually process and relationship. The fixes differ.
• Cash per day = Annual fees / 365. Every day of lock-up removed releases that amount of real cash, no new clients required.
• Model improvements in dollars: days saved x cash per day. In our example, modest cuts freed roughly $2m, enough to fund drawings and reduce partner capital tied up.
• Faster collection is not the same as writing off fees. One releases cash you earned; the other is a loss. Keep them separate on the report.