Calculating your target heart rate
Here is a quick and simple way to calculate your target heart rate:
Males: Begin with 220
Females: Begin with 224
Subtract your age, which will give you your maximum heart rate.
Multiply your maximum heart rate by 0.60 for your low end
Multiply your maximum heart rate by 0.85 for your high end
Goal is to stay within this target zone for maximum health and physical benefits.

[...] Add an additional 15-20 minutes on to your regular cardio routine, you are already there (remember, resting metabolic rates are higher in those who exercise and have more muscle mass), if you are short on extra time then increase the intensity of your daily workout while staying within target heart rate zone. [...]