When shifts stay open, the instinct is to ask whoever works the most. The better question is whose limit is actually in the way. We tested every person on one cafe roster: free them up to work any time, then separately raise their weekly cap to 40 hours, and rebuild the week each time.
The roster builder's built-in invented example: a seven-person cafe, 32 shifts, 235 hours to cover, a 10-hour rest gap. It starts with 3 shifts open, 216 hours covered and $3,622 payroll. For each person we changed one thing and rebuilt, leaving everything else as it was.
| Person | Free at any time | Weekly cap raised to 40 h | ||||
|---|---|---|---|---|---|---|
| Open | Hours | Payroll | Open | Hours | Payroll | |
| Ana | 3 | 216 | $3,622 | 3 | 216 | $3,622 |
| Ben | 3 | 216 | $3,622 | 2 | 224 | $3,750 |
| Cleo | 1 | 232 | $3,870 | 3 | 216 | $3,622 |
| Dev | 3 | 216 | $3,620 | 3 | 216 | $3,622 |
| Eli | 2 | 224 | $3,736 | 3 | 216 | $3,622 |
| Fay | 3 | 216 | $3,622 | 2 | 224 | $3,746 |
| Gus | 3 | 216 | $3,622 | 3 | 216 | $3,622 |
Only a few changes matter. Freeing Cleo, who is limited to evenings on weekdays, closes two of the three open shifts and lifts coverage to 232 hours. Raising the cap for Ben or Fay, who sit below 40 hours, closes one open shift each. Ana and Gus, the two people with the widest availability, change nothing either way: they were never the bottleneck. And freeing Ben, Dev or Fay changes nothing in coverage (Dev saves $2). This is one invented example, not a benchmark, and your own constraints decide who the right person is.
List the shifts you could not fill and the reason each fails: nobody available, hour cap, or rest gap.
If the reason is an hour cap, ask the people near their cap. If it is availability, ask whoever is free just outside the shift.
Confirm that the change would fill the shift without creating overtime or breaking a rest gap, so the ask is specific.
Rebuild the week once per person with that person free at any time, and compare open shifts. The person whose change closes the most open shifts is the one to ask. Often it is not the person with the most hours already; it is the one whose current availability misses the shifts nobody else can take. The roster builder shows which shifts stay open and why, which points at who to ask.
Check whether the cap is what blocks the open shifts. In the example, raising the weekly limit for the two people sitting at their cap closed one open shift each, while raising it for people with room to spare changed nothing. Try the change in the tool before you ask.