Somebody texts at 6am that they are not coming in. You have two moves: patch (give that one shift to someone else and touch nothing more) or rebuild (mark the person off and re-plan the week, which can move other people's shifts). Which one works depends mostly on how full the week already was. We measured it.
The roster builder's built-in invented example: a seven-person cafe, 32 shifts, 235 hours to cover, a 40-hour overtime line and a 10-hour rest gap. We took every person-day on the finished roster (each is one possible call-out) and tried both moves, with the rest of the week fixed. Then we added one spare part-timer (15 an hour, up to 24 hours, free any time) and ran it again. “Covered” means the move created no new open hours.
| Staff | Possible call-outs | Patched with one swap | Rebuild covers it | Shifts a rebuild moves |
|---|---|---|---|---|
| The cafe as given | 29 | 0 | 24 | 2 to 19 |
| Plus one spare part-timer | 32 | 1 | 18 | 13 to 24 |
A one-for-one swap almost never works on a week that was built to use everyone: the people who are free that hour are already at their weekly limit, on another shift, or inside their rest gap. A rebuild finds a cover far more often, but it is not free. It re-plans the whole week, so it moved between 2 and 24 shifts, which is a lot of text messages. Rebuilds find cover for 24 of 29 call-outs on the cafe as given. Adding a spare part-timer does not raise that share (18 of 32) in this example, and it makes each rebuild move more people. The practical lesson is to decide in advance who your first call is, and to treat a rebuild as a last resort once the swap list comes back empty. This is one invented example, not a benchmark, and your own availability decides your numbers.
Test a call-out on your own week
Write down everyone whose availability covers the whole shift, who is not already working then, and who still has hours under their weekly limit.
Cross out anyone who would then work less than your minimum rest gap before or after, and price anyone who would go into overtime against leaving the shift one person short.
Ask whether a person who cannot take the shift can give up a lighter shift to someone who can. The roster builder lists these trades.
Find who is free, under their hour limit and rested enough to take the shift. If nobody is, rebuild the week with the absent person marked off, which can move other people's shifts. The roster builder does both: the sick-call finder lists who can take a shift, and an off: entry rebuilds around the absence.
Ask the people whose availability and weekly hours leave room first, since they cost no overtime. If the shift is thin rather than empty, leaving it short for one day is sometimes cheaper than paying overtime. Check the rules where you operate before asking anyone to work extra.