These three come up constantly and none of them is a variant of 2-2-3. Each solves a different problem, and each has an arithmetic cost you should see before it reaches payroll.
3 x 12 with a split weekend
A fixed three-shift week where the nurse works one weekend day and is off the other, every week, instead of alternating whole weekends on and off.
The arithmetic is 3 shifts of 12 hours, so 36 hours each week and no designed-in overtime under a 40-hour workweek. The weekend benefit is coverage: every nurse contributes one weekend day per week, so a Saturday or Sunday post draws on the whole crew instead of on whichever half is scheduled that weekend. The cost is that nobody ever gets two consecutive weekend days off. Teams that value a real weekend usually prefer alternating full weekends and accept the harder Saturday.
DDNN rotation
Two 12-hour days, two 12-hour nights, then four off, on an 8-day cycle.
Four 12-hour shifts in 8 days is 48 hours per cycle, which averages 42 hours per week — the same average as 2-2-3, 4-on/4-off, and DuPont. The average is not what payroll sees: because the cycle drifts across the calendar, individual workweeks alternate between 36 and 48 hours, so every other week carries 8 overtime hours under a 40-hour workweek. The distinctive feature is that the day-to-night turn is built into every single cycle. A nurse finishing the second day shift at 19:00 starts the first night shift at 19:00 the following evening, then finishes the block at 07:00 with a four-day recovery window. Whether that is humane depends on whether the four days off are protected. If your call-out process routinely reaches into the off block, DDNN stops being a recovery pattern and becomes a fatigue pattern.
4-on / 5-off
Four 12-hour shifts, then five days off, on a 9-day cycle.
Four shifts in 9 days is 48 hours per cycle, or about 37.3 hours per week on average. That average is the part people quote and the part that misleads. A 9-day cycle does not line up with a 7-day workweek, so the pattern drifts: some payroll weeks contain four shifts (48 hours, producing 8 overtime hours above 40) while others contain three or even two (36 or 24 hours, none). The long-run average sits below 40 while individual weeks still trigger overtime. Before you standardise on this, run a full 63-day span — seven cycles, nine weeks — through the pay system and look at the weekly totals rather than the average.
Four consecutive 12-hour shifts is also a genuine fatigue question, not a scheduling preference. Set the consecutive-shift limit in your own schedule rules where you can defend it, and make exceptions visible.