Does a person weighing 300 pounds pay twice as much as a 150 pound person?
Actually, it may cost as much as ten times more than a person of average weight.
Obviously, it's going to depend a lot on what type of life insurance plan the person buys - for instance, accidental death insurance, it's not going to matter much, how unhealthy you are - the odds of you dying by accidental death will not change much based on your health or weight.
But for any significant amount of life insurance, more than $10,000 that you can get with a "guaranteed issue" type of life insurance policy, any type that's going to be medically underwritten, if you can qualify for the policy, it can easily cost 5 or 10 times more.
A type 1 diabetic may pay many times more for life insurance than a diabetic, even if the person is not obese.
However, an obese person may want to buy a guaranteed issue life insurance policy now, and then meet with his/her doctor to develop a healthy and safe program to lose weight.
Once the person has lost some weight, he can contact life insurance companies and try again to qualify for life insurance coverage at better rates than offered to someone who is considered obese by the BMI (Body Mass Index) charts used by life insurance companies to determine who is overweight, or considered obese for life insurance rating purposes.