Calculate your ideal body weight
With this calculator you can calculate your ideal weight. The ideal body weight is the weight, which theoretically will give you the longest life with the least diseases.
The calculator and the theory behind it illustrates that many people might not have the need for weight loss they think they do.
How to calculate
Enter gender, height and body type in the calculator. Body type is your own assessment of whether you have a small/thin or wide/heavy skeletal structure. You must ignore your body fat in this assessment. You might base your assessment on how you looked when you were younger.
Background for the calculator
The calculation of ideal body weight is based on what is the optimal BMI in relation to the likelihood of a long life with the least diseases. Recent large studies indicate that the lowest mortality actually occurs at BMI values close to overweight. However, one should not for that reason pursue an overweight BMI, as there are problems associated with obesity that are unrelated to mortality. This could be issues with osteoarthritis, physical activity, sleep and non-fatal diseases.
In this calculator ideal body weight is set, so that it takes into account lowest mortality as well as other problems that may be linked with obesity. Since BMI is misleading for people with either a light or a heavy skeletal frame, adjustment for body structure is included.
What is the optimal BMI for men and women?
If one looks broadly at the core studies, it is reasonable to conclude that the optimal BMI is between 20 and 27. In studies that have gone deeper into the difference between men and women, it seems that either the same optimal range applies or that men are 2-5 BMI points higher. In the calculator the ideal BMI is set to 22.5 for women and 24.5 for men.
| Reference | Optimal BMI range |
| JAMA 2013 | All: 25-30 |
| BMC MRM 2011 | Female: 20.1-24.6 Male: 26.4-27.5 |
| NEJM 2010 | Female: 21,3-26,3 Male: 22.5-28.8 |
| Lancet 2009 | All: 22.5-25.0 |
| NEJM 2006 | Female: 23.5-26.4 Male: 25.0-27.9 |
| NEJM 1999 | Female: 20.5-24.9 Male: 22.0-26.4 |
The new very large study from JAMA 2013 overestimate the benefits of overweight, because overweight is compared with normal weight defined as BMI 18.5 to 25 We know from other studies that mortality is significantly elevated for BMI values between 18.5 and 20 The range we usually consider normal weight therefore include BMI values far from optimal.
How big is the uncertainty of ideal body weight?
In most studies, the risk only slightly increases if the BMI value is a few BMI points from the optimum. This effectively means that if your actual weight is within +/- 12 lbs (6 kg) of ideal weight, it is still within the optimal range.
What is the influence body structure?
If you're looking at body structure as differences in frame size / width of skeleton, then the original ideal weight tables from the 1960s had a correction of plus-minus 10 % of body weight. If you look at recent studies, it appears to be the norm, that differences in skeletal width can affect body weight 6-8 % in each direction. This calculator therefore has a built in adjustment of plus-minus 8 %.
Should you drink cream if you are too light?
No, even if your body weight is 10-16 lbs (5-8 kg) under your ideal weight, it should not be your goal to increase your body fat, but rather your lean body mass. The best thing you can do is to eat enough healthy food and do activities that increase your muscle mass.
Should you go on a diet if you are too heavy?
From a health point of view - probably not. If your BMI is above 30 and you have low muscle mass and lifestyle diseases such as type 2 diabetes, then you should consider to lose weight, but otherwise not. Dieting will for most people be harmful in the long term.
Difference between smokers and non-smokers
For smokers or former smokers the lowest mortality rates are seen at higher BMI values than for non-smokers. The explanation is partly that smokers often develop diseases (eg. COPD), resulting in low body weight. Smokers that are not yet sick will probably be in a better position to cope with future disease if their body weight is in the overweight range. Ideal values in the calculator is set against a mixed population of smokers, ex-smokers and never-smokers.
Influence of age
In general, the optimal BMI increases with age. Roughly speaking, one can say that young people should preferably be in the normal weight range and older people in the overweight range - at least in terms of the overall mortality. Also for older people one should still remember that obesity can cause other problems such as problems related to the musculoskeletal system and the ability to be mobile.
Overall conclusion
There are many indications that we should adjust our limits for what is considered a healthy BMI. Generally, a BMI between 20 and 30 should not cause concern if you are in all other ways healthy. Even if you have a BMI between 30 and 35 and are otherwise free of any disease, then it might still be a bad idea to go on a diet. Especially because we know that repeated dieting is short-term healthy, but long-term harmful. The studies also clearly shows the increased risk of having a very low body weight and therefore this calculator is also intended to help normal-weight people to understand that they should not lose weight.
References
Association of all-cause mortality with overweight and obesity using standard body mass index categories: a systematic review and meta-analysis.
Flegal KM et al.
JAMA. 2013 Jan 2;309(1):71-82.
Examining the BMI-mortality relationship using fractional polynomials.
Wong ES et al.
BMC Med Res Methodol. 2011 Dec 28;11:175.