Firstly, I stay away from the word ‘workout’ because it is nebulous. Sometimes, it doesn’t mean anything at all.
I prefer ‘train’ instead. I train for something specific: to be as strong, fast, and agile as I can possibly be. I have a training program designed for me, by a Coach, that has been tested and proven by others, not just me. On this program, I record my progress and vary my training periodically so that it stays fresh and keeps me improving measurably, all the time.
‘Train’ will never mean ‘go to the gym, wander around, look at your phone periodically, and do a few exercises randomly.’
Now that we have our definitions (for the purposes of this post; yours may vary) out of the way, we can proceed. This brings us forward towards the answer, in fact.
When you are training (as defined above) the number of days you need to train per week is quite clear.
When you’re just ‘working out’, well, it doesn’t seem to matter so much, or be as clear.
But OK I’ll take it easy on you: let’s say that you still just want ‘the answer’ and you are not training towards any goal, on any program. All you want to know is, ‘how often should you workout’?
It still depends on what you are doing, among other factors.
Let me try to answer another way; with some general common sense:
Moving your body around every day is important. The more that you drive or sit, the more you have to combat the effects of driving and sitting. Keep in mind that ‘moving’ does not mean ‘bench press’. Types of movement that your body likes include: walking, crawling, lunging, twisting, pushing, pulling, throwing, hanging, pressing, holding, carrying, playing, stretching, and mobilizing, to name a few.
When it comes to weight and cardiovascular training, in broad strokes, noting that the quantity and quality of each can vary widely, these are not things that you need to do every day in order to achieve basic fitness goals. I can make that statement because I have achieved them myself on three day per week programs, and seen others do so even on two day per week programs, although that is more rare and not recommended for beginners. Three to four days should be enough.
But can you workout with positive results six or seven days per week? Yes, you can, although again, not recommended for beginners. I like six, mixing up three days with weights, and three days without, including as many sports and ‘extra’ work as possible.
To be honest, you shouldn’t workout 3.5 days per week if you are not making any progress, or have no idea what you are doing.
You should be improving 1-2% every time you set foot in the gym.
But don’t just take my word for it.
“When you improve a little each day, eventually big things occur. When you improve conditioning a little each day, eventually you have a big improvement in conditioning. Not tomorrow, not the next day, but eventually a big gain is made. Don’t look for the big, quick improvement. Seek the small improvement one day at a time. That’s the only way it happens — and when it happens, it lasts.” —John Wooden
Among others. You can Google the rest.