This is one of the most common questions we get asked from friends, family and clients. While the easy (and still true) answer is “it depends”, we're going to give you more meat than that because that answer won’t do you much good.
Instead, we'll break it down for you based on your current level of activity and goals:
Currently Inactive If you haven’t had a consistent routine going within the last couple months, let alone years, then you just need to get the ball rolling. Many people will say that you should just start with something, but I want to be real with you; if you really want to make a change then you should start with 2 days per week of structured exercise.
Spend the majority of these 2 days lifting weights that are challenging to you and add a little cardio to the end of your workout. Try to make each exercise session last 45min-1 hour and choose weights that are about a 7 or 8 on a scale from 1-10. If you can keep this up for 6 weeks consistently, then you can add a third day to the mix.
Currently Exercising 1 or 2 Days Per Week It’s great that you have some consistency going, and you have likely seen a little progress, but that has probably stalled at this point. If you are happy with your current state, keep going with it. However, if you are still trying to lose fat or gain muscle then you should know that you must have more frequency.
Based on experience, 3 days per week of strength training seems to be the sweet spot for most people to get appreciable results. Like training two times per week, you should spend the majority of your training session lifting weights that are challenging and getting a little cardio towards the end of your workout. It is best to have a day in between training sessions, and if you can find a fourth day to workout then you should focus on cardio that day.
Currently Exercising 3 or 4 Days Per Week If you are already training 3-4 days per week and have been doing so for a fair amount of time, then you most likely have seen some significant results. If not, then you should probably take a look at your nutrition or other areas that are likely holding you back. Conversely, if you are close to reaching your goals but need just a little bit more than you should bump your training up to 5 workouts per week.
This is where your goals really start to determine how you spend your sessions. If you are working on losing that last little bit of fat, then you should lift weights for 45-60 minutes three days per week and log two days of cardio at 30-45 minutes per bout. If your primary goal is to build more muscle, then you should spend 4 sessions lifting weights and perform 45-60 minutes of cardio on your fifth day. Unless of course you prefer to lift weights all 5 days.