Three sessions is the sweet spot

Two sessions a week maintains; three progresses; four or more produces diminishing returns for most people unless sessions are short or deliberately varied in intensity.

The reason is that Pilates fatigues the small stabilizing muscles, and those recover more slowly relative to their size than the large movers do.

A week that works

Vary the emphasis rather than repeating the same session. The overlap between them is substantial, so nothing gets neglected.

A sustainable weekly structure
DaySessionFocus
MondayReformer, 45 minFull body — footwork, core series, arms
TuesdayRest or walk
WednesdayReformer, 45 minLower body and core
ThursdayMat, 25 minControl and mobility
FridayReformer, 45 minUpper body and posture
WeekendRest, or one light sessionRecovery

Progression over a block

Progress by adding range and control before adding spring. A full-range exercise on two springs is almost always more valuable than a partial-range one on three.

Reassess every six weeks. If everything feels comfortable, that is the signal to add load or complexity rather than volume.