The first thing you have to ask yourself when answering this question is, what is your goal?
If your goal revolves around as simple as just wanting to be healthy, proper nutrition & 2-3 days of exercise will do.
Look at your day to day life right now. How much planned exercise are you getting, if any? If you are then just build off of that or vary it up. Do you walk, then try adding a day of biking. Do you run, add in 1-2 days of strength training. Do you strength train, add in 1-2 days of aerobic exercise. I think you get the point. Doing this will help keep your current routine fresh and depending upon what mode you add in you’ll elicit a different physiological response.
Let’s say you aren’t exercising at all, start SMALL! If you want to start walking regularly, biking, swimming, weight training, etc… set a goal you know you can achieve. More than likely you can give up 30-60 minutes twice a week for your health, there’s no magic number. Setting this small goal and sticking with it for 4-8 weeks DILIGENTLY will give you a sense of accomplishment and the itch to add in more and not quit.
Let’s go the opposite route, you try and commit to 60minutes of exercise 5 days a week. The first week you kill it, on top of the world. The second week is the same. The third week though you stay late at work, soreness is catching up to you, you’re tired, you miss a day. The next day you say you’ll do it tomorrow and then tomorrow turns into the weekend, the weekend into next week, annnnnnnd then you fall off. Lasted 2 full weeks. Congrats you’ve played yourself.
Pick one type of exercise you are going to commit to, add in 2 days for 30-60mins to start. I can almost guarantee you will succeed in making it a routine for the, well, rest of your life.