You can lose 20 lbs in three months if you go for proper calorie intake and regular exercise. You can calculate your daily calorie intake by calculating basal metabolic rate (BMR). You have not indicated your gender and lifestyle in your question, that is why I have not calculated your daily calorie intake. You can calculate your basal metabolic rate by following formula.
BMR for Men=66+(13.7 X wt in kg)+(5 X ht in cm)-(6.8X age in years)
BMR for women =655+(9.6 X wt in kg)+(1.8 X ht in cm)-(4.7 X age in years).
Now multiply your BMR with activity multiplier.
Sedentary = BMR X 1.2, Lightly active = BMR X 1.375,
Moderate Active = BMR X 1.55, Very active = BMR X 1.725, Extraordinary active = BMR X 1.9.
In this way you can calculate your daily calories requirements. If you want to reduce or increase weight then put your desired weight in the weight space of the BMR formula.
BMR for Men=66+(13.7 X wt in kg)+(5 X ht in cm)-(6.8X age in years)
BMR for women =655+(9.6 X wt in kg)+(1.8 X ht in cm)-(4.7 X age in years).
Now multiply your BMR with activity multiplier.
Sedentary = BMR X 1.2, Lightly active = BMR X 1.375,
Moderate Active = BMR X 1.55, Very active = BMR X 1.725, Extraordinary active = BMR X 1.9.
In this way you can calculate your daily calories requirements. If you want to reduce or increase weight then put your desired weight in the weight space of the BMR formula.
