Trying to figure out what the right amount of exercise might be for your body and your needs can be a little difficult. Because at the end of the day we are all different, we all have different demands on our lifestyles, therefore varying amounts of time, and we all have different fitness goals. If you were to follow what the Department of Health and Human Services recommends, then a healthy adult only requires 150 minutes of moderate aerobic exercise, or 75 minutes of vigorous aerobic activity.
This advice is fine for an otherwise healthy adult who merely wants to maintain their current health. The problem is that if you have specific fitness goals, such as shedding a few kilos, building body strength and endurance or tightening up certain areas of your body, and you spend most of your days working in front of a computer, then this amount of exercise is not really going to help you achieve your goals.
When it comes to general health, I believe a healthy adult should participate in a minimum of 30 minutes of moderate to vigorous aerobic activity per day. However if you are a person who tends to put weight on more quickly than others, or you are working to burn off some unwanted weight then increasing this to a minimum of 45-60 minutes per day will be very beneficial.
If you are training to prepare your body for a specific event, or working towards a specific fitness goal, then you will also have to consider this when deciding what the right amount of exercise is for you. This may vary depending on your goals, however if you are training specific parts of your body, it is important to consider your rest days and how you may incorporate active recovery on those days to help support you towards your fitness goals.
All in all I recommend a minimum of 30 minutes of exercise per day; in order to maintain pre-existing good health, longer for those working to achieve it, and any more than 30 minutes will be helping you towards achieving your fitness goals!