Sandy McFadden

This is a very simple plugin which requires almost no configuration.
All you need to do is go to the Appearence then Widgets area in the Admin Dashboard. 
Once you are there drag the BMI Calculator widget onto the widget area you would like it added to.
The only two settings are the title and the color. The color is the hex color you would like the results background to be.
A lot of the code was adapted from 
<a href="http://codereview.stackexchange.com/questions/21581/calculating-body-mass-index-bmi" title="Inspiration Code" rel="nofollow ugc">Stack Exchange Thread</a>

Healthy BMI Calculator

Adds a shortcode and widget that will display a simple BMI Calculator on your site. Works with both metric and US style measurements.

Mortgage Calculator

bmiberegner

The most complete free BMI calculator for WordPress with built-in translations and as the only plugin we include BMI calculation for adults and children based on the WHO BMI classification.

BMI Adult & Kid Calculator

We have developed a free Wordpress plugin with our BMI Calculator that you can use completely free of charge.

Healthy BMI Calculator vs BMI Adult & Kid Calculator