Working out how many days per week?

Anonymous
What's the ideal amount? Generally I do chest day twice per week, arms one day, back and shoulders, sometimes intermixed in some combination, and throw in a cardio day or do a bit of cardio with weight lifting... but usually I'll go 4 days per week.

This last week I was a little bit lazy, although I had to work late 2 or 3 nights so I was a bit tired after that. But I don't know, is this generally good?
Updates
+1 y
Sometimes soreness creeps in a little worse than usual too, so sometimes I feel it's better to rest an extra day or two.
Working out how many days per week?
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