Using either the Harris-Benedict or Katch-McArdle formulas, enter the requested body stats and your desired fat loss below. The calculator will then give you an estimated caloric intake for you to reach your desired fat loss.
It is important to note that your results on the scale will not be identical to your fat loss. Scales can be discouraging and misleading unless you understand the nature of fat vs. muscle weight. See my Weight Loss Versus Fat Loss below for more information.
Know your body fat percentage? You can use the Katch-McArdle formula, which should be more accurate.
Your Height (feet and inches)
Your Activity Level Definitions
The one thing that makes losing fat mildly pleasurable (other than the hard-won results) is using oneself for scientific exploration. Sadly, nutrition and health science information is hard to pin down. There are a lot of companies hoping you’ll stay confused. Also, every person’s body is different and there are countless factors to a person’s health. To top it off, it seems nutrition is hardly an exact science even under the best circumstances. Nonetheless, I’ve compiled what I believe to be something quite close to the truth regarding fat loss for most people.
Weight Loss Versus Fat Loss
Normally this calculator would be called a "weight-loss" calculator. But that title would be misleading at best. Most of us don’t really want to lose weight, we want to lose fat! Weight can come in many forms: muscle, fat, bones, etc. Some of that weight can be detrimental to health and appearance (fat) and some of it can be great (muscle). Losing fat is great. Keeping and/or gaining muscle is a good thing, and if you gain enough of it, you may even gain "weight"!
If you’ve landed on this page, you surely already know that losing fat is a function of burning more Calories than you consume in a given day. So I won’t belabor the point. Reinforcing this idea, here is an extremely short article on the Mayo Clinic’s site indicating that fat loss is all about Calories and not any other factor, including exercise! So to lose fat, you want to burn more Calories than you consume, creating a deficit. Exercise can help you do this. Read on.
A Pound of Fat
One pound of fat contains 3,500 Calories. Eating 3,500 Calories less than you use over any period of time will result in a loss of one pound of fat over that period of time (whether it be a week or a month).
Maximum Safe Fat Loss
I like to take things to logical extremes. So how far can a Calorie deficit be taken? Well, the body apparently cannot survive on your fat reserves alone. So after a certain point, it turns to other sources for fuel, namely your muscle! This process is called catabolism. Losing muscle is exactly what we don’t want to do when dieting, so we need to know where the muscle burning threshold lies. Unfortunately, finding a one true answer to this question is next to impossible. But here is what I have found:
- According to Bryner RW. Journal of the American College of Nutrition 1999;18(1):115-121, the threshold may be as low as 800 Calories a day, but only when combined with resistance training (weightlifting)!
- This article, citing a study in Journals of Gerontology, indicates that lean body mass in humans (based on rat research) can be maintained with a daily 40% Calorie reduction (example: 2,500 Calories reduced to 1,200). However, it points out that an 8% reduction (from 2,500 to 2,300) would be both safer and easier over long periods of time.
- An article from the Army Physical Fitness Research Institute containing a chapter titled The Nutrition Connection by Lori D. Hennessy and Gaston P. Bathalon states that "Minimum Calorie intake levels for weight loss are 1,500 Calories a day for men and 1,200 Calories a day for women." It also lists a table of acceptable weight loss for the various branches of the US military. The most extreme is the Navy/Marines at 1 – 2 pounds/week or 1% body weight every 2 weeks.
- A typical articles based on "research" but with no specific cites such as this one typically state that 1,200 (women) and 1,500 (men) Calories are a minimum for keeping lean body mass (muscle).
From this and other articles and books I’ve read, I think we can safely conclude that 1,200-1,500 Calories is a good general minimum daily intake to avoid the loss of muscle (assuming normal activity levels). Below those amounts, weightlifting will probably help stave off muscle loss. Below 800 Calories a day, resistance training may work but you’re on your own because no scientist has tread there yet.
Exercise is not essential to losing fat. That can be done with dieting alone. However, exercise can help burn fat and is important in changing your body’s appearance.
Preventing Muscle Loss
Depending on how much you decrease your daily Calorie intake to create a deficit and burn fat, you may find yourself in danger of burning muscle for fuel (catabolism). To be on the safe side you can add exercise to your routine to stave off muscle loss. The best exercise for this purpose is weightlifting.
Even better than preventing muscle loss is building new muscle. Not only will this have an immediate positive effect on the appearance of your body (and you’ll be stronger!), you’ll also burn more Calories all day - even while you sleep. Wondering how much? Well, believe it or not, researchers don’t all agree on the exact amount. But it’s somewhere around 5-6 Calories per day per pound of muscle. By comparison, each pound of fat burns around 2 Calories per day. For one piece of research on this, see The underappreciated role of muscle in health and disease by Robert R Wolfe. As with preventing muscle loss, the type of exercise you’ll want to perform to build muscle is weightlifting (or other resistance training). As with everything else in this field, nobody agrees on the best way to lift weights, so you’ll have to do your own research and come to your own conclusions. As a general rule, I recommend 4-7 exercises involving the major muscle groups in a workout lasting around 20 minutes.
Exercise isn’t just for building muscle. It can also be used to burn Calories directly. Weightlifting burns Calories (typically a couple hundred per workout). Vigorous aerobics (with your heart rate around 150 beats per minute for a half hour) burns a lot of Calories. How many depends on your weight and difficulty level, but 200-500 would be common.
Obviously, if you burn 300 Calories while jogging or biking, you can (and perhaps should) eat an additional 300 Calories during the day. At the very least, this makes dieting just that much easier.
The other benefit of aerobic exercise is that you will build up your physical endurance, lower your blood pressure, and probably increase your all-day metabolism (experts seem to agree on this) which helps you burn yet more Calories. Note that dieting generally lowers your metabolism as your body tries to cope with the lower food energy intake.
To lose fat, eat less Calories. To make sure you lose fat and not muscle, try exercise (particularly weightlifting). This will also help you burn Calories. Try writing down the Calories you eat on a daily basis. This is not fun, I know, but it is the only way to be sure. You may be surprised which foods are adding up and which ones aren’t too bad! My weight can fluctuate up to 5 pounds in one day. Don’t let the scale discourage you. If you’re in a Calorie deficit, the science says you will be losing fat! Let the science do its thing!
A note on fasting
Counting calories requires enormous willpower.
Intermittent fasting (Wikipedia) is an alternative strategy. People like myself find it far easier to go an entire day without eating than it is to "eat right" in a calorie deficit. There is a lot of information about IF. Stick with the science. 24 hour fasts are extremely well studied since they are used often as a preparation for medical tests and treatment in hospital settings.
In addition to helping jump-start a serious calorie deficit, fasting for short periods of time may have all kinds of additional benefits. Again, stick with peer-reviewed, large-scale studies (that is, actual science!).
The IF link above and this one on fasting in general (Wikipedia) are both fantastic starting places with pointers and references to relevant science.