Billing increment chart: 5, 6, 10 and 15 minutes

A firm that bills in increments does not bill the minutes a task took. It turns each time entry into a whole number of units and bills those units at its hourly rate. In six-minute units rounded up, any task that took from 13 to 18 minutes reaches the bill as 0.3 hours, and the client sees the units without the minutes behind them.

The gap between the time worked and the time billed is therefore decided by two choices that are made before anyone records an hour: the size of the unit and the way an entry is rounded to it. The calculator above shows both for a single entry, including how many minutes the rounding added, and the chart shows the result for every amount of time up to an hour. For the exact decimal of a time without any unit, use the minutes to decimal converter.

Six-minute units are small enough that rounding adds little to a long piece of work, and they keep every entry to one decimal place. A fee of 0.3 hours at 400 an hour is 120.00, which anyone can check by hand. That is why most firms in the US and the UK record time in tenths, and why many corporate clients write tenths into the billing guidelines their outside lawyers have to follow.

Rounding up counts every started unit in full, so a seven-minute call bills as 0.2 hours in tenths. Rounding to the nearest unit takes half a unit or more up and anything less down, so the same call bills as 0.1, and only a call of nine minutes or more becomes 0.2.

The difference shows over a month of entries. Rounding up adds close to half a unit to every entry, about two and a half minutes in tenths and seven minutes in quarter hours, and never takes anything away. Rounding to the nearest unit adds to some entries and takes from others, so the total stays close to the time worked. It does, however, turn very short entries into nothing: in tenths, a task of one or two minutes rounds to 0.0, which is why firms that round to the nearest unit usually bill at least one unit for any entry.

Whether a firm rounds each entry or rounds the day's total for a matter makes more difference than the size of the unit. Every rounded entry can add almost a whole unit, so the cost of rounding grows with the number of entries rather than with the time worked.

Ten emails of two minutes each on one matter show the effect. They are 20 minutes of work. Rounded up one by one in tenths, they bill as 1.0 hour, but added up first and rounded once, they bill as 0.4. In quarter hours the gap is wider still, with 2.5 hours against 0.5.

Clients who audit legal bills look for exactly this pattern of many short entries at the minimum unit. A firm that rounds each entry should say so in its engagement letter, and short tasks should be recorded against the matter when they happen rather than estimated at the end of the day. The time to decimal calculator rounds each entry before it adds them up, so it shows the effect on a day of your own, and Sixminute writes each entry in the firm's unit from the time actually worked.

Only six-minute units give whole tenths. Ten-minute units bill in sixths of an hour (0.17, 0.33 and 0.5), fifteen-minute units bill in quarters (0.25, 0.5 and 0.75), and five-minute units bill in twelfths that need two decimal places: 0.08, 0.17 and 0.25.

Those two-place decimals are themselves rounded, and the rounding reaches the invoice. Five minutes is really 0.0833 hours, so a billing system that multiplies 0.08 by a rate of 300 an hour charges 24.00 for a unit that is worth 25.00, and twelve such units add up to 0.96 hours instead of a full hour. When the unit does not divide into tenths, the fee should be calculated from the number of units or from the minutes, and only the final amount rounded.

The coarser the unit, the more a short task costs. Rounded up, a two-minute call bills as 5 minutes in five-minute units, 6 minutes in tenths and 15 minutes in quarter hours, so the quarter-hour unit bills the call at seven and a half times the time it took.

To round a number of minutes up to tenths in Excel or Google Sheets, round it up to a multiple of six and divide by 60. With 13 minutes in A2, =CEILING(A2,6)/60 gives 0.3. To round to the nearest tenth instead, use =MROUND(A2,6)/60, which takes 9 minutes to 0.2 and 8 minutes to 0.1. For another unit, replace the 6 with 5, 10 or 15.

If the column holds times such as 0:13 rather than a number of minutes, convert each time to minutes first. A spreadsheet stores a time as a fraction of a day, and that fraction does not always multiply back to an exact whole minute, so round it before rounding to the unit: =CEILING(ROUND(A2*1440,0),6)/60 turns 0:13 into 0.3.