Sandy McFadden

This is a great plugin which will help you keep track and brag about the progress you make as you start losing weight or getting healthy. 
You get to decide which measurements you want to keep track of and you can change them at any point.

Health Progress

Health Progress will add a widget and shortcode to your site which will display your starting measurements and progress as you get healthy.

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.

Health Progress vs Healthy BMI Calculator