If you have ever read a legal invoice, you have seen entries like "Telephone conference with client, 0.2" or "Review and revise motion, 1.4." Those decimals are not arbitrary. They are the visible surface of the most widespread convention in hourly professional billing: the six-minute increment. Law firms use it almost universally, as our guide to time tracking for lawyers explores, and many consultants, accountants, and other hourly professionals have adopted it as well. This post explains exactly what the convention means, how the rounding works, how to convert minutes to tenths without thinking hard, and why the system exists in the first place.
What a six-minute increment actually is
An hour contains sixty minutes, and one tenth of sixty minutes is six minutes. A six-minute increment is therefore simply one tenth of an hour, written as 0.1 on a timesheet or an invoice. Every duration you bill is expressed as some multiple of that tenth. A task recorded as 0.3 hours took three increments, or eighteen minutes. A task recorded as 1.5 hours took fifteen increments, or ninety minutes.
The reason for using tenths rather than minutes is arithmetic. Hourly billing means multiplying time by a rate, and multiplying $300 per hour by 47 minutes requires converting the minutes to a fraction of an hour first. Expressing the time as 0.8 hours makes the math immediate: 0.8 multiplied by $300 is $240. Decimal hours turn every line of an invoice into a one-step multiplication, which mattered enormously in the era of paper ledgers and still matters for anyone reviewing a bill.
How the rounding convention works
Real work does not arrive in clean six-minute blocks, so every increment system needs a rounding rule. The standard convention in legal billing is to round each task up to the next full increment. The logic is that any amount of work within an increment consumes that increment, in the same way a one-day car rental bills for the full day whether you drive it for one hour or ten.
Under the round-up convention, the conversion from actual minutes to billed tenths looks like this:
- A task lasting 1 to 6 minutes bills as 0.1 hours.
- A task lasting 7 to 12 minutes bills as 0.2 hours.
- A task lasting 13 to 18 minutes bills as 0.3 hours.
- A task lasting 19 to 24 minutes bills as 0.4 hours.
- A task lasting 25 to 30 minutes bills as 0.5 hours.
- A task lasting 31 to 36 minutes bills as 0.6 hours.
- A task lasting 37 to 42 minutes bills as 0.7 hours.
- A task lasting 43 to 48 minutes bills as 0.8 hours.
- A task lasting 49 to 54 minutes bills as 0.9 hours.
- A task lasting 55 to 60 minutes bills as 1.0 hours.
Some firms use round-to-nearest instead, under which an eight-minute task bills as 0.1 rather than 0.2 because eight minutes is closer to six than to twelve. Round-to-nearest is friendlier to clients and is sometimes required by corporate billing guidelines, but round-up remains the dominant convention. Whichever rule you use, the essential requirements are that you disclose it, typically in the engagement letter, and that you apply it uniformly to every task and every client.
Worked examples with real dollar amounts
Concrete numbers make the system intuitive, so consider an attorney billing at $300 per hour, which makes each tenth worth $30. A four-minute phone call rounds up to 0.1 hours and bills at $30, and our guide on how attorneys bill for phone calls covers these entries in depth. An eleven-minute call rounds up to 0.2 hours and bills at $60. A twenty-minute document review rounds up to 0.4 hours and bills at $120. A fifty-minute drafting session rounds up to 0.9 hours and bills at $270.
Now run a full example across a morning. Suppose you take a nine-minute call from a client at 8:50, spend thirty-two minutes revising a contract, answer a client email that takes five minutes, and then spend one hour and ten minutes preparing for a deposition. The call bills as 0.2, the revision as 0.6, the email as 0.1, and the preparation as 1.2, for a total of 2.1 hours. At $300 per hour, the morning is worth $630. Notice that the actual working time was one hour and fifty-six minutes, and the billed time is 2.1 hours. The five extra tenths of an hour are the cumulative effect of rounding up four separate tasks, which is precisely why the rounding rule must be disclosed and applied consistently.
Why the convention exists
The six-minute increment survives because it balances three competing needs at once:
- Precision. Tenths of an hour are fine-grained enough to bill short tasks honestly. A quarter-hour system, by contrast, turns a three-minute call into a fifteen-minute charge, which quintuples the rounding error and invites disputes. This is the main reason legal billing standardized on tenths rather than the quarter-hour increments common in some other trades.
- Simplicity. Decimal hours multiply cleanly against hourly rates, sum cleanly across a day, and read cleanly on an invoice. Nobody has to do base-sixty arithmetic to check a bill.
- Fairness in both directions. The increment compensates the professional for the fixed cost of every task switch, since even a two-minute call requires stopping other work, engaging with the matter, and resuming afterward. At the same time, the small unit size keeps that compensation proportionate.
The part nobody tells you: increments make small tasks billable
Here is the practical consequence of everything above, and it is the one that changes behavior. Under a six-minute increment system, there is no such thing as a task too small to bill. The two-minute call, the ninety-second text exchange about a filing deadline, and the quick email reply each round up to 0.1 hours. At $300 per hour, each one is worth $30.
Yet these are exactly the tasks that never reach invoices, because they feel too trivial to write down at the moment they happen. The increment system says they are worth $30 apiece; the timekeeping habit treats them as worth nothing. An attorney who handles six such micro-tasks a day and logs none of them is quietly forfeiting 0.6 billable hours daily, and the arithmetic over a working year is painful to contemplate. We break down where that time goes in our post on the five ways billable time leaks out of your week.
Closing that gap is a capture problem rather than a math problem, the problem at the center of our guide to capturing every billable hour. Short tasks evade manual timers because no one starts a timer for a two-minute call, and they evade end-of-week reconstruction because memory discards them first. Studies of professional timekeeping consistently find that reconstructed timesheets understate the hours actually worked, and the smallest tasks account for a large share of the shortfall. This is the specific problem TrackTime was built for. Its Android app automatically captures the categories of small work that leak the most: inbound and outbound phone calls timed and matched to clients, SMS conversations and incoming RCS messages in Google Messages, time spent working in Gmail and Outlook, and drive time for client trips. Captured entries appear in the web dashboard, where you review them, round them to your increment policy, and turn them into invoices with the built-in invoicing tools. Privacy is metadata only: the service stores who, when, and how long, and never stores message contents or email subject lines. One honest limitation is worth stating plainly: this works on Android because Android permits it, and it cannot work on iPhone because iOS does not allow any app to observe calls, messages, or foreground apps at the operating-system level.
Common mistakes to avoid
- Rounding twice. Round each task once, from its actual duration to the next tenth. Do not round the raw time up to a tenth and then round the daily total up again; the double rounding inflates the bill and will not survive an audit.
- Estimating instead of measuring. Rounding is only defensible when it starts from a real duration. An attorney who guesses that a call took "about ten minutes" and bills 0.2 is stacking an estimate on top of a rounding rule, and estimates made from memory usually run short rather than long.
- Fragmenting one task into many increments. If you make five two-minute calls on the same matter in one hour, billing five separate 0.1 entries is technically consistent with a round-up policy, but many clients and courts view deliberate fragmentation as abusive. When short tasks on one matter cluster tightly, the safer practice is to record them as they occurred and exercise judgment about consolidation before invoicing.
- Hiding the policy. The increment and the rounding rule belong in the engagement letter. Clients accept rounding they were told about and dispute rounding they discover.
Frequently asked questions
What does 0.1 hours mean on an invoice?
It means one tenth of an hour, which is six minutes of billed time. It usually indicates a short task, such as a brief phone call or email, that took six minutes or less and was rounded up to the minimum increment. At a rate of $300 per hour, a 0.1 entry costs $30.
How do I convert minutes to decimal hours quickly?
Divide the minutes by six and round up to the next whole number, and that number is your tenths digit. For example, twenty-two minutes divided by six is a little under four, so it rounds up to four tenths and bills as 0.4 hours. With a little practice the conversion becomes automatic, and good billing software applies the rule for you.
Are six-minute increments better than fifteen-minute increments?
For the client, almost always. A fifteen-minute increment turns every short task into a 0.25-hour charge, so the rounding overhead is much larger and invoices drift further from the time actually worked. Six-minute increments keep billed time close to real time, which is why they are the standard in legal billing and a sensible default for any hourly professional.
Is rounding up to the next increment ethical?
Yes, provided the increment is reasonable, the policy is disclosed to the client in advance, and it is applied consistently from accurate underlying durations. Rounding becomes a problem when it is stacked on inflated estimates, applied twice, or used to fragment continuous work into many minimum charges. The rule of thumb is simple: the rounding convention should be something you would be comfortable explaining line by line to the client who is paying the bill.
Make the increments work in your favor
Six-minute increments mean every small task you perform has a real dollar value, but only if it gets captured. Start a free 7-day TrackTime trial and let a week of automatic capture show you how many billable tenths you are currently giving away, or see how the Android app works.
