Before changing to a more fit lifestyle, it is a good idea to find out what your BMR, Basal Metabolic Rate, and BMI, Body Mass Index, are.
Calculating the Basal Metabolic Rate will help you understand how many calories you burn when you are at rest. The more fit and active you are, the more calories you burn just sitting around. If you want to bulk up, consume a greater number of calories than your BMR burns and than you burn off in a workout. To lose, consume less. To maintain, try for equilibrium.
Body Mass Index is a somewhat less accurate determination of whether you are or are not “healthy” which caclulates a ratio of weight to height. If you weigh too little for your height, the chart indicates “underweight.” “Normal” is considered the appropriate weight for height, and “overweight” and “obese” follow. The obvious flaw with BMI as a hard and fast rule for what is “normal” is that bodies are not all built “normally.” A bodybuilder may register as overweight with very little body fat. However inaccurate, BMI is still a good basic number to calculate, particularly if you need to lose weight.
While surfing r/fitness on Reddit, I came across a post from a redditor who created his own graphically pleasing (free!) BMR and BMI calculators located at FitCal.me Of course you could figure it out with your own calculations, but why not let someone else do the work?
Remember when using any calculators, they do not represent or replace medical advice.