You're asking about "how long", with something that has "in a week" already in the question - you might want to rethink that.
Anyway, trying to lose 20 lbs in a week is unhealthy, very, very difficult and very unlikely to either succeed or give a lasting result.
Aim for losing 1-3 lbs/week instead, which is fairly easy on a sensible diet. You'll reach your goal in a couple of months anyhow, with a much greater chance of both success and a sustainable result.
it will take around 20 weeks at 2 pound a week which is the remented amount to lose a week , however at the start of a diet you will must likely lose 5 pound which will be most water weight so around 18.5 weeks to lose 40 pounds
I did 20 minutes on my treadmill , 4 days a week, and lost about one pound a week.
If you can find a good diet then you lose 2 pounds a week in for the first 4 weeks then it slows to 1 pound a week. So it will take roughly 20 weeks.
In general, it's better to lose weight slowly; most doctors will suggest 1-2 pounds a week. At one pound a week, it would take about a year and a half to lose 71 pounds.
IF you want to loose a pound in a week the first thing you have tyo do is figure out your current calorie intake then you have to take out about 200 calories each day and over a week or so your body will adjust and you will start to lose weight.
a week
There are 3500 calories in one pound. Cutting 500 calories a day would make you lose one pound each week.
A pound of fat is generally around 3500 calories, so to lose a pound of fat a week you would need to lose 500 calories a day
You can lose up to 10 pound a week by doing that :)
It vaires per person and based on their own individual habits. If is it just an extreme diet, they may lose a pound every week or two. If they are intensely exercising and really restricting their food intake they may be able to lose a pound or two every week.
To lose one pound a week, you need to consumer 3500 calories a week fewer than you burn. You can do this by creating a calorie deficit of 500 per day. 500 x 7 = 3500 and that's a pound.
you will lose about 5 pounds. Because for every 3400 calories you burn it is a pound, so take 17500 and divide it by 3400