The arithmetic, done once
Work in minutes and convert at the end. A shift from 8:45 to 17:20 is 515 minutes. Take off a 45-minute unpaid lunch and you have 470 minutes, which is 7.83 hours to two places. Doing it the other way around, subtracting 0.45 from 8.58, produces a number that is close enough to look right and wrong enough to matter over a month. Repeat per day, sum the minutes for the week, and convert once. If your shift crosses midnight, add 24 hours to the end time before subtracting, so 22:30 to 06:15 becomes 30:15 minus 22:30, which is 465 minutes, or 7.75 hours.
Which minutes actually count?
In the US, the Fair Labor Standards Act draws the lines, and the Department of Labor's Fact Sheet 22 states them plainly. Short rest breaks, usually 20 minutes or less, count as hours worked. Bona fide meal periods, typically 30 minutes or more, generally do not, but only if the employee is completely relieved from duty; someone who eats at the desk and keeps answering the phone has not been relieved, and that time counts. Ordinary commuting from home to work is not work time. Travel from job site to job site during the workday is. Rules differ elsewhere, so check your own jurisdiction before treating any of this as settled where you are.
Waiting, on-call and training
The same US fact sheet separates being engaged to wait, which is work time, from waiting to be engaged, which is not. Someone reading a book between tasks at their post is working. An employee required to stay on the employer's premises while on call is working; one who can leave and simply be reachable generally is not, unless the constraints on their freedom are tight enough to change the answer. Attendance at lectures, meetings and training only falls outside working time when it is outside normal hours, voluntary, not job related, and no other work happens at the same time. All four conditions have to hold at once, which is rarer than people assume.
Why the weekly total is the one that matters
US overtime is assessed on a fixed, recurring 168-hour workweek, not on a day and not on a pay period, and hours cannot be averaged across two or more weeks. So a daily total is a working figure and the weekly total is the one with consequences. In the UK the framing is different again: the 48-hour limit is an average, normally taken over 17 weeks, which makes a single long week unremarkable and a long quarter significant. Whichever applies to you, the practical consequence is the same. Record the days as you go, because reconstructing a week from memory on Friday is where the error enters.
In short
- Work in minutes, convert to decimal hours once at the end, and add 24 hours to an end time that crosses midnight.
- In the US, short breaks of about 20 minutes or less count as hours worked; genuine meal periods of 30 minutes or more generally do not. Rules differ elsewhere.
- Eating at your desk while still handling work is not a bona fide meal period under US rules.
- Home-to-work commuting is not work time; travel between job sites during the day is.
- The US workweek is a fixed, recurring 168-hour period and hours may not be averaged across weeks.
Related guides
- Decimal Hours, Explained: Decimal hours express a duration as a single base-10 number, because 7:45 cannot be multiplied by a rate but 7.75 can.
- Overtime Basics: Overtime rules are national, not universal.
- What Makes a Good Timesheet: A good timesheet carries a date, a start time, an end time, any unpaid break, a daily total and a period total, plus whatever the work is attributed to.