Rotating shift patterns: covering the posts and balancing the hours

Updated: 2026-08-13 · ISKRIT

Covering a post around the clock is arithmetic before it is scheduling. The number of crews follows from the hours the post must be manned and the hours one person may work, and every pattern in use is a solution to that one equation.

How many crews a post needs

A post manned continuously consumes 168 hours a week. A full-time worker supplies roughly 40. Four crews therefore cover 160 and leave a gap that overtime or a fifth crew has to fill. This is why continuous operations settle on four crews with planned overtime or five crews with slack, and never on exactly four with no overtime.

Why hours balance over a period, not a week

No rotating pattern gives the same hours every week. A four-on four-off cycle produces weeks of 36 and 48 hours in alternation, and neither is the contracted week. The accounting therefore runs over a period long enough for the cycle to complete: a quarter or a year, depending on the pattern and what the contract allows.

Two consequences follow, and both surprise people. Overtime is the excess over the period norm, not over 40 in any one week, so a 48-hour week inside a balanced quarter is not overtime. And an employee who leaves mid-period has to be settled against the hours actually worked against the norm to that date, which is a calculation nobody wants to do by hand.

The rules that shape the pattern

Rest between shifts, consecutive night limits, weekly rest and the length of a single shift are constraints, not preferences, and they eliminate most patterns before scheduling starts. The one that catches people out is the changeover: rotating forward, from nights to days, gives a short rest at the turn unless the pattern builds in a free day. A pattern that looks balanced on the hours can still be unworkable at exactly one point in the cycle.

Forward or backward rotation

Rotating forward, days to evenings to nights, follows the body clock and is generally tolerated better than the reverse. Backward rotation compresses rest at every changeover. The choice affects absence and error rates more than the hours do, and it costs nothing to get right at the design stage.

Coverage before fairness

A roster that treats every crew identically is fair and often fails, because posts differ: some need a qualified person on every shift, some do not run at weekends. Coverage is a hard constraint and fairness is an objective, and solving them in the wrong order produces a pretty roster with a hole in it.

The shift schedule generator builds the pattern from the posts and the crew size, reports the hours against the period norm rather than against the week, and flags the changeover where rest falls short.