Glossary · Receivables metrics
Lock-up
Also called Lock-up days
Lock-up is the number of days between doing work and being paid for it: unbilled work-in-progress days plus debtor days.
Lock-up is the standard cash measure in UK professional services, especially law and accountancy firms. It adds work-in-progress days — how long work sits before it is billed — to debtor days — how long bills sit before they are paid.
It captures a delay that DSO misses. A firm can collect promptly after invoicing and still be short of cash because it bills weeks after the work is done.
Reducing lock-up has two levers: bill sooner, with interim or monthly billing, and collect faster once billed.
Because both halves are measured in days of fees, lock-up converts directly into cash. A firm billing €1 million a year — about €2,740 a day — that cuts lock-up by 10 days frees roughly €27,000.
Formula
Lock-up days = work-in-progress days + debtor days
Example
A law firm’s unbilled time equals 25 days of fees and its debtor days are 60. Lock-up is 85 days: nearly three months between the work and the cash.