Shift Overlap & Gap Calculator

Where two shifts are on together it is overlap; where nobody is on, it is a gap

If shift A runs 8:00 AM–4:00 PM and shift B runs 3:00 PM–11:00 PM, the hour from 3:00 PM to 4:00 PM is 1 hour of overlap. From 11:00 PM to 8:00 AM nobody is on shift, so 9 hours of the day are uncovered. Someone is working for 15 hours (8:00 AM–11:00 PM), and because each shift is 8 hours, the total staff hours, counted per person, come to 16.

The dial works like a clock face with midnight at the top and the day running clockwise. The coloured arc on the inner ring is each shift, and the height of the outer band shows how many people are on at that moment. Hatched stretches are uncovered, and the darker fill marks hours where two or more shifts overlap. The schedule is assumed to repeat every day, so a shift from 10:00 PM to 6:00 AM is drawn as one arc and is not cut at midnight.

When it pays to check overlap and gaps

A rota can look fine row by row and still hide a hole between two shifts or a handover that is longer than anyone planned. Lining the shifts up in time order helps most in these situations.

• Work that needs a handover: wards, control rooms and production lines depend on the outgoing shift briefing the incoming one. If one shift ends at the exact minute the next begins, overlap is 0 minutes and the schedule has no time for the handover.
• Posts that cannot be left empty: security desks, 24-hour shops and phone lines. An uncovered stretch is time when nobody can respond, and the list of gaps tells you exactly which hours need another person.
• Busy periods that need more than one person: a shop with lunch and evening rushes is not empty with one person on, but it is stretched. Set a required headcount and every stretch below it is reported separately as understaffed.
• Keeping labour cost in check: during overlap two shifts are paid for the same work. If the overlap is longer than the handover needs, moving a start or end time by a few minutes cuts the total staff hours.

How the calculation works

1. Convert times to minutes. 3:30 PM is 15 × 60 + 30 = 930 minutes. A day runs from 0 to 1,440 minutes.
2. Work out each shift's length. If the end is later than the start, it is end − start. If it is earlier, the shift finishes the next day and 1,440 minutes are added. For 10:00 PM–6:00 AM that is 360 + 1,440 − 1,320 = 480 minutes, or 8 hours.
3. Cut the day at every boundary. Every start and end is marked on the 24-hour ring, and for each piece between two marks the calculator counts the shifts and the people on duty. A start time counts as on shift, an end time does not.
4. Add up the pieces by status. A piece with no shift is a gap, a piece with two or more shifts is overlap, and a piece with fewer people than required is understaffed. Even if three shifts overlap, that stretch is counted once in the overlap.
5. Total staff hours are counted separately. This is each shift's length times its headcount, added together. It uses the whole schedule even when you narrow the range to operating hours.

Gap = Σ piece length (0 shifts) · Overlap = Σ piece length (2 or more shifts) · Understaffed = Σ piece length (people < required) · Total staff hours = Σ shift length × people

Gap plus hours with someone on shift equals the whole range being checked (24 hours for a full day). Overlap sits inside the hours with someone on shift, so adding all three together comes to more than 24 hours.

Overlap and gaps in common shift patterns

Two 3-shift rotas can give very different results depending on whether the shifts meet exactly or overlap by 30 minutes. The table below uses a full 24-hour day and one person per shift. A back-to-back handoff is a place where one shift ends at the minute the next one starts, so the handover time is 0 minutes.

A 12-hour two-shift pattern and a 3-shift pattern with shifts meeting exactly both show a gap of 0 minutes, so the rota looks seamless. But they contain 2 and 3 back-to-back handoffs, which means no scheduled handover time. The 3-shift pattern with a 30-minute handover creates that time, at the price of 8.5-hour shifts. In the last row, three shifts bunched in the middle of the day overlap for 8 hours and still leave 14 hours uncovered.

With a required headcount, an overlap can still be short

Say a shop is open 10:00 AM–10:00 PM and needs 2 people at all times. Two people open from 9:30 AM to 3:30 PM, one person works mid from 12:00 PM to 6:00 PM, and two people close from 4:00 PM to 10:30 PM. There is no uncovered time inside opening hours, but from 3:30 PM to 4:00 PM only the mid shift is left, one person short of the requirement.

Starting the closing shift at 3:30 PM brings the shortfall to 0 minutes, and the two closers each work 30 minutes more, so total staff hours rise by 1 hour. In the other direction, if some of the 5 h 30 min of overlap falls in a quiet spell, the mid shift can be trimmed there. When you set operating hours, anything outside them (the closers tidying up from 10:00 PM to 10:30 PM) is left out of the gap, overlap and shortfall figures. Total staff hours still cover the whole schedule.

Handover time: what to keep in mind in the UK and the US

A handover is only real if one shift stays on or the next shift arrives early. Both are time at work, so a longer overlap lengthens somebody’s day. In the UK, regulation 10(1) of the Working Time Regulations 1998 gives a worker a rest period of at least 11 consecutive hours in each 24-hour period. If you move a late finisher’s end time later to make room for a handover, check that the gap before their next start still leaves 11 hours. The calculator does not test this for you, so compare the end of one day with the start of the next by eye. A 10:30 PM finish followed by a 6:00 AM start leaves only 7 hours and 30 minutes.

In the United States the Fair Labor Standards Act counts overtime by the workweek: covered, non-exempt employees must be paid at least one and a half times their regular rate for hours worked over 40 in a workweek. A 30-minute handover on every shift therefore matters when it pushes an employee past 40 hours in the week. State laws can add their own rules, so check the state where the work is done.

With a 30-minute handover on the 3-shift rotation, the daily overlap is 1 hour 30 minutes. With one person per shift, that is 547 hours 30 minutes over a 365-day year during which two shifts are paid for the same work. Overlapping only where a handover is truly needed, and letting other changeovers meet exactly, keeps the handover while trimming the cost.

Breaks can create gaps

In Great Britain, regulation 12 of the Working Time Regulations 1998 says that where a worker’s daily working time is more than six hours, the worker is entitled to a rest break. Unless a relevant agreement says otherwise, it is an uninterrupted period of at least 20 minutes, and the worker may spend it away from the workstation. The regulation does not say whether that break is paid, and that is a matter for the contract.

Federal law in the United States does not require lunch or coffee breaks. If an employer does give short rest periods of about 20 minutes or less, they count as hours worked. Bona fide meal periods, typically 30 minutes or longer, generally do not, as long as the employee is completely relieved from duty.

If you are the only person on shift, a break is a real gap. To see it in the calculator, split one shift into two rows. For a 7:00 AM–4:00 PM shift with a break from 12:00 PM to 1:00 PM, enter 7:00 AM–12:00 PM and 1:00 PM–4:00 PM, then check the flow list to see whether anyone covers the middle hour. Where two or more people work together, staggering their breaks is usually enough to prevent a gap.

Entering night shifts, and how UK and US rules differ

To enter a shift that crosses midnight, type the real start and end, for example 10:00 PM and 6:00 AM. When the end is earlier than the start, the calculator treats it as finishing the next day, gives it 8 hours, and draws it as a single arc across midnight. The English version of this tool does not add up night hours, because there is no single night period that applies to everyone.

In the UK, regulation 2 of the Working Time Regulations 1998 defines night time as a period of at least seven hours that includes midnight to 5:00 AM, as set by a relevant agreement. If no agreement does so, it is 11:00 PM to 6:00 AM. A night worker is someone who normally works at least three hours of their daily working time during night time.

In the US the position is simpler: the Fair Labor Standards Act does not require extra pay for night work, so any night premium is a matter of agreement between the employer and the employee. Whether a shift counts as night work and what it earns therefore depends on the contract or agreement, not on the clock alone.

Common calculation mistakes

• Reading total staff hours minus hours with someone on shift as the overlap. In the three-shift example the total is 24 hours and someone is on for 10, a difference of 14. But two or more shifts are together only from 9:00 AM to 5:00 PM, 8 hours. The difference is bigger because the stretch where all three overlap is subtracted twice.
• Assuming a back-to-back change has handover time. If one shift ends at 2:00 PM and the next starts at 2:00 PM, the overlap is 0 minutes. The flow list marks it as a straight handoff with 0 min overlap.
• Counting closed hours as gaps. Unless you are open 24 hours, switch the range to operating hours so only the hours that really are uncovered are left. Operating hours can also cross midnight, for example 8:00 PM–4:00 AM.
• Assuming overlapping shifts are enough people. Two shifts with one person each make 2 people. If 3 are required, the overlap is still understaffed. Enter the headcount and the requirement to see the difference.
• Entering a 24-hour shift with the same start and end. 8:00 AM–8:00 AM could mean 0 minutes or a full day, so it is flagged as an error. If it really is a 24-hour shift, press “Count as a 24-hour shift” under the row.

Limits and cautions

• The schedule is assumed to repeat at the same times every day. If the rota differs by weekday, group the days that match and calculate each group separately.
• Times are to the minute and up to 20 shifts can be entered. One shift cannot be longer than 24 hours.
• A day is always 24 hours. For clock-change days or shifts in different time zones, convert everything to one time zone first.
• Breaks, travel and time away from the post are not removed automatically. Split a shift into two rows if you need to show them.
• The result is a count of clock time. It does not decide what counts as working time, whether overtime is due or whether any rule has been broken.
• Entries are calculated in this browser only and are not sent to a server. The schedule goes into the address only when you press “Copy link”.

Rules checked on 22 October 2026: regulations 2, 10 and 12 of the Working Time Regulations 1998 (SI 1998/1833) on legislation.gov.uk, and the US Department of Labor pages on breaks, night work, hours worked and overtime under the Fair Labor Standards Act.

Sources

• 01legislation.gov.uk: Working Time Regulations 1998, regulation 2 (interpretation)“Night time” is at least seven hours including midnight to 5 a.m. as agreed, otherwise 11 p.m. to 6 a.m.; a night worker normally works at least three hours of daily working time at night
• 02legislation.gov.uk: Working Time Regulations 1998, regulation 10 (daily rest)Rest period of not less than eleven consecutive hours in each 24-hour period
• 03legislation.gov.uk: Working Time Regulations 1998, regulation 12 (rest breaks)Daily working time of more than six hours: an uninterrupted break of not less than 20 minutes unless an agreement says otherwise, away from the workstation
• 04US Department of Labor: Breaks and Meal PeriodsFederal law does not require lunch or coffee breaks; short breaks offered by the employer count as work time
• 05US Department of Labor: Night Work and Shift WorkThe FLSA does not require extra pay for night work; overtime is time and one-half the regular rate over 40 hours in a workweek
• 06US Department of Labor: Fact Sheet #22, Hours Worked under the FLSARest periods of 20 minutes or less count as hours worked; bona fide meal periods, typically 30 minutes or more, generally do not

Frequently asked questions

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