How to Calculate Hours for Overnight Shifts

To calculate an overnight shift, add 24 hours to the end time before subtracting the start time, then subtract any unpaid break. A shift from 10:00 PM to 6:30 AM with a 30-minute unpaid break is (6:30 + 24:00) − 22:00 − 0:30 = 8 hours. The arithmetic is the easy part. The harder questions are which day and which week the hours belong to, and what happens on the two nights a year when the clocks change.

The basic calculation

Work in the 24-hour clock so you can't mix up AM and PM:

1. Convert both times to 24-hour format: 10:00 PM is 22:00, 6:30 AM is 06:30.
2. If the end time is earlier than the start time, the shift crossed midnight, so add 24 hours to the end: 06:30 becomes 30:30.
3. Subtract: 30:30 − 22:00 = 8 hours 30 minutes.
4. Subtract unpaid breaks: 8:30 − 0:30 = 8:00.
5. For payroll, convert minutes to decimal hours by dividing by 60 (see minutes to decimal hours).

A common mistake is subtracting the clock times directly: 6:30 − 10:00 gives −3.5, and dropping the minus sign gives 3.5 hours instead of 8.5.

Which day do the hours belong to?

For a weekly total it rarely matters. But if you're paid overtime by the day, or your shift crosses the end of the workweek, it does.

The workweek boundary (US federal rule)

Under the Fair Labor Standards Act a workweek is a fixed, recurring period of 168 hours that can start on any day and at any hour, and each workweek stands alone. Hours are generally counted in the workweek in which they're worked. If your workweek starts at 12:00 AM Sunday, a Saturday 10:00 PM to Sunday 6:00 AM shift puts 2 hours in the week that is ending and 6 in the new one.

Example. You've worked 38 hours by Saturday evening and then work that 8-hour overnight shift. If the whole shift counted in the first week you'd have 46 hours and 6 hours of overtime. Split correctly, the first week has 40 hours and no overtime, and the 6 hours start the new week. That isn't your employer cheating; it's how the workweek works. But it is worth knowing where yours begins (ask payroll).

The workday (California and other daily-overtime rules)

California pays overtime after 8 hours in a workday, defined as any consecutive 24-hour period that starts at the same time each day. If your employer's workday starts at midnight, a 6:00 PM to 6:00 AM shift is 6 hours in one workday and 6 in the next, so no daily overtime is owed for a 12-hour shift. If the workday starts at 6:00 PM, the same shift is 12 hours in one workday: 4 hours of daily overtime. Employers are allowed to set the workday start, but it has to stay fixed. See California overtime rules.

A shift that runs across two workdays is not a "split shift" under California law: the California Court of Appeal said so in Securitas Security Services USA, Inc. v. Superior Court (2011). Split shifts are covered in split shift pay.

When the clocks change overnight

On the nights daylight saving time starts or ends, the clock on the wall and the hours you actually work differ by one hour. Pay rules are based on the time actually worked:

• Clocks go back (autumn): one hour happens twice (1:00 to 2:00 AM in North America and the UK). A 10:00 PM to 6:00 AM shift is 9 hours of work, not 8.
• Clocks go forward (spring): one hour is skipped (2:00 AM jumps to 3:00 AM in North America; 1:00 AM to 2:00 AM in the UK). A 10:00 PM to 6:00 AM shift is 7 hours of work, not 8.

US federal law requires pay for all hours worked, so on the autumn night the extra hour must be paid (and counts toward weekly overtime). Whether a salaried worker or someone on a fixed shift payment gets more or less pay in spring depends on the contract. Many time clocks record elapsed time correctly, but a handwritten timesheet or simple "end minus start" calculation, including ours, uses the clock on the wall. Add or subtract the hour yourself on these dates.

The transitions happen in the early hours of each Sunday listed, so the affected shift is the one that starts on Saturday night. Arizona (except the Navajo Nation), Hawaii, most of Saskatchewan, and Queensland, Western Australia and the Northern Territory don't change their clocks. We worked out these dates from the IANA time zone database used by computers worldwide.

Breaks, rest and night pay

• Breaks follow the same rules as day shifts: in the US, short rest breaks are paid and genuine meal breaks of 30 minutes or more usually aren't. See are breaks paid?
• Rest between shifts is protected in some places: 11 hours in the UK, and in Ontario 11 consecutive hours off each day and 8 hours between shifts (with exceptions). The US has no general federal rule.
• Night premiums aren't required by US federal law, but many employers pay a shift differential. If yours does, it raises your overtime rate too. See shift differential pay.

Calculate an overnight shift

The Hours Worked Calculator spots an end time earlier than the start time and treats it as an overnight shift automatically. For a full week of night shifts with overtime and pay, use the Time Card Calculator, which handles overnight shifts on every row.

Sources

• 29 CFR §778.105 — Determining the workweek
• US Department of Labor — Fact Sheet #22: Hours worked under the FLSA
• California Code of Regulations, Title 8, §11040 — definition of workday
• Securitas Security Services USA, Inc. v. Superior Court (Cal. Ct. App. 2011)
• IANA Time Zone Database (daylight saving dates)
• GOV.UK — Rest breaks at work
• Ontario — Hours of work (rest periods)