For anyone who sells their time, the gap between hours worked and hours invoiced is where the money goes. Work happens in fragments: a nine-minute call, a twenty-minute review, an interruption that turns into an afternoon. Tracking billable hours is the discipline of catching those fragments while they are still visible, because by Friday afternoon perhaps a fifth of them have vanished from memory altogether and can never be charged for.

This guide covers what qualifies as billable work, the six-minute and fifteen-minute increments and what each costs you, why recording as you go beats reconstruction, how utilisation is measured, and how to write an entry a client will pay without querying. Individual spans can be measured with the free hours between two times calculator.

What Are Billable Hours?

Billable hours are the portions of working time that can properly be charged to a client under an engagement agreement. Everything else, from business development to internal meetings and administration, is non-billable, even though it is real work that has to happen.

The boundary is set by the agreement, not by effort. Travel is often chargeable at a reduced rate or not at all; time spent correcting your own error is not chargeable at any rate; and work done before an engagement letter is signed frequently cannot be recovered. The habit worth forming is to record everything and classify it as billable or not afterwards, because a fragment that was never written down cannot be reclassified into revenue later. Recording it also gives you an honest picture of where the working day actually goes, which is usually more surprising than people expect.

Six-Minute Versus Fifteen-Minute Increments

Two units dominate professional practice, and the choice between them has a measurable effect on both revenue and client goodwill:

  • Six minutes, or 0.1 of an hour: the standard in law and much of accountancy. It maps cleanly onto decimal hours, so 18 minutes is 0.3 and 42 minutes is 0.7.
  • Fifteen minutes, or 0.25 of an hour: common in consultancy and agency work. Simpler to record, but it rounds a four-minute email up to a quarter of an hour.
  • One minute, or exact time: used where a timer runs continuously. The fairest to the client and the least forgiving of sloppy note-taking.
  • Hourly blocks: occasionally used for retained or fixed-scope work, where the increment matters far less than the total.

The arithmetic deserves a moment's attention. A practitioner handling forty short tasks a week under fifteen-minute increments can invoice several hours that were never worked, which clients notice and challenge; the same practitioner under six-minute increments captures the small work honestly and loses far less billable time to unrecorded fragments. Whatever unit is chosen, it must be stated in the engagement terms and applied consistently, never varied by client or by how the month is going. Converting the raw minutes is a mechanical step covered in converting minutes to decimal hours.

Why Contemporaneous Recording Beats Reconstruction

Record time as the work happens, or within a few minutes of finishing it. Reconstructed billable hours are consistently lower than contemporaneous ones, and the loss is not evenly spread: short tasks disappear entirely while long ones are remembered as rounder and shorter than they were.

There is a second reason beyond revenue. A contemporaneous entry is evidence, and where fees are reviewed, audited or challenged, an entry written at 14:20 on the day carries a weight that a Friday reconstruction never will. Reconstruction also invites its own quiet dishonesty, since a person filling gaps from memory tends to fill them with what should have happened. Three habits make this practical: start a timer before opening the file, write the entry before starting the next task, and never let more than one day pass unrecorded. The same argument for daily entry applies to employment timekeeping, as set out in how to use a timesheet.

What Is a Good Utilisation Rate?

The utilisation rate is billable hours divided by total available working hours, expressed as a percentage. Somewhere between 60 and 80 percent is typical for fee earners, and a sustained figure above about 85 percent usually signals that non-billable work is simply not being recorded.

It is worth keeping utilisation distinct from two neighbouring measures. Realisation is the proportion of recorded billable hours that actually appear on an invoice after write-offs. Collection is the proportion of invoiced amounts that are eventually paid. A practice can post excellent utilisation and still lose money if half the recorded time is written off before billing, which is why the three figures are read together rather than alone. Utilisation is also a poor target to manage people by in isolation, because the fastest way to raise it is to stop recording the administration, training and supervision that keep the practice functioning.

Writing Time Entries a Client Will Pay

A billable entry survives review when it names the task, the subject and the output. "Reviewed and annotated draft supply agreement, clauses 4 to 9, and prepared note of amendments for client call" reads as work; "attention to file" reads as padding and is the single most commonly written-off phrase in professional billing.

  1. Start with a verb. Drafted, reviewed, attended, analysed, negotiated. It states immediately what was done.
  2. Name the document or matter. Specificity is what lets a reviewer connect the entry to something they recognise.
  3. Give the output. A note, a filing, a decision, a revised draft. Work with a visible product is rarely challenged.
  4. Avoid block billing. A single four-hour entry covering five unrelated tasks is much more likely to be cut than five separate entries.
  5. Write in plain language. The reader is often a finance manager rather than a specialist.

Tools and Habits for Tracking Billable Hours

The tool matters less than the moment of capture. A timer that is one click away will be used; anything requiring a login and three dropdowns will not, and the entry will be reconstructed at the end of the week instead. Start simple: a running clock, a plain daily log, and a weekly total.

A browser-based punch in and punch out clock is enough to capture start and stop times for a day's work, while the time to decimal converter turns those spans into the billing unit. Review the log once a week, before invoicing, and look for the two failure patterns: days with suspiciously round totals, and gaps of an hour or more with nothing recorded against them. Both are almost always unrecorded work. When the volume outgrows a simple log, the question of moving to dedicated software is covered in free time clock versus payroll software.

Conclusion

Tracking billable hours well comes down to four habits: capture the time as it happens, use a stated increment and stick to it, keep utilisation honest by recording non-billable work rather than hiding it, and write entries that name the task, the subject and the output. Six-minute units lose less than fifteen-minute ones and generate fewer arguments. Measure any span with the free hours between two times calculator, or see the other tools on timeclock.now.