How long should you stay in a calorie deficit?
It depends!
It depends on how much fat you have to lose, and how big of a calorie deficit you choose.
If fat loss is your goal, you can lose fat faster with an aggressive calorie deficit
But with larger deficits, you wouldn't be able to eat as much. One thing I can advise in general is that the calorie deficit is usually in the 15% to 30% below maintenance range. This is 500 to 750 calories under maintenance, which tends to be the most common. That being said, it does depend on how aggressive you want to be and whether you think you may have hunger issues on larger deficits. One thing I can advise almost everyone when asked how much cardio they should do is that almost every health and fitness organization in the world suggests that you get moderate exercise(equivalent to a brisk walk) at least 5 days a week for 30 minutes (150 min). This is not only good for your health but also great for helping with fat loss. Then you need to decide what type of cardio exercise is best for you. Many people struggle with choosing what type of cardio exercise is best for them and their fat loss goals.
You could choose walking or something more intense. For example you might prefer to do a elliptical machine or choose the stairclimber, which is one of my favorites for fat loss. Or maybe you like the intensity and efficiency of interval training? Maybe you enjoy classes or group exercise of some sort. I could go on and if that list of all the options for cardio. So if choosing a type of cardio exercise is confusing or leading to indecision, then a great question is.... "what do you enjoy?" This is the best method to choosing the right cardio for weight loss, rather than looking for any so called perfect or optimal cardio plan. And also remember that nutrition is the number one priority when it comes to fat loss That's because you could do 5, 6, 7 days a week of cardio, but if you eat too much you still wont lose any fat or your fat loss will be reduced. Cardio alone doesn't lead to fat loss, a calorie deficit does. Cardio is simply a tool to help you increase your calorie deficit above what you could get with diet alone, assuming you dont eat back those calories burned!