Day 46: The Real Math, Calculating Goal Weight Based on Body Fat Percentage

Yesterday, while I was discussing my belief that body fat percentage remains my priority, I started to think about what my goal body fat percentage is. How much body fat should a grown up, athletic woman like myself shoot for? I searched the internet and found many different charts. This is the one that seems to be reasonable to me, and is based on gender/age and whether or not you want to be “average” or more lean.

Body Fat Chart

I was trying to work backward and find out how to calculate how much weight I would need to lose, given maintaining my current lean muscle mass, and was a bit surprised. However, I’m not sure that the number I have for myself  includes bones and other lean tissue. But, based on that and my goal body fat content of somewhere around 24, I might need to lose an additional 10 pounds. That being said, I’m doing NO exercise right now until I have the ol’ knee surgery. I build muscle very easily, so I have a feeling my goal weight will be dead on when I regain some muscle.

Here’s how you calculate, according to Marc Perry at

To find your lean muscle mass: Take your body weight right now and multiply it by the body fat percentage your scale shows (or your trainer has given you). Now, subtract that number from your current body weight.

Say you weigh 200 pounds. Your body fat percentage is 45%. (200 X .45 = 90) Then, take your body weight (200 – 90 = 110). You have 110 pounds of lean body mass! Great, now what? How do you figure out your goal weight?

So, say you think your goal body fat percentage should be 29%, which is average for a 26-30 year old woman. You first will subtract your desired body fat percentage from 1. (1-.29=.71) Now, divide your lean body mass (in pounds) by the .71. (110/.71= 154) So, if your muscle mass (or lean body mass) remains the same, your goal weight is 154. At that weight you should be at a body fat percentage of 29%. Isn’t that cool?

Marc has the formulas all spelled out on his site.

To me, body fat percentage is what it’s about. BMI is total horse dinky. It does NOT take into account your lean mass. If they went strictly by BMI, athletes like Lance Armstrong would be obese. Remember the whole muscle weighs more than fat thing?

I hope this helps you guys like it helps me focus. It’s not the pounds as much as the lean pounds to fat pound ratio that I’m truly concerned with… well, until that scale doesn’t move. THEN, I must remember to revisit this post and adjust my thinking from somthing less emotional to something a little more cerebral.

OR the other option is to go have an iDXA scan, which I did last year. Oh, the humiliation! However, I posted my scanned image which I think is fascinating and would be totally awesome if I didn’t know who that was in the picture. I do plan to do another scan at the end of this year come hell or high water. I want to see the difference!

Carry on!


Now I Know

Today, I drove to the University of Texas Fitness Institute and had my (iDXA)  body composition scan. I faced it. I don’t like what it said, but, there it is in living color. The 7 minute scan is pretty much like a bone density scan, with low radiation. It’s a non-invasive scan, but let me tell you, there’s no way to hide… no sucking in will help. Considered to be very accurate, it gives you reports on the fat in various parts of your body including legs, arms torso and hips. They even estimated the amount of visceral fat in your abdominal cavity near your organs. UGH.

The good news is that I have good bone density and a high amount of lean muscle mass. The bad news is that I’ve got a long way to go. I knew that, but here it is staring me in the face with real, indisputable numbers. My goal is to make my body fat number go down, a lot, while maintaining my lean muscle mass.

It was obvious to Julie, my fitness guru, that I know what I’m supposed to be doing and I like to exercise. I tend to think I’m doing it, but I’m really inconsistent. For the next 3 months, I will do my weight workouts twice a week and my cardio at least 3 times, probably more. I will track my exercise in My Fitness Pal (50poundMonkey) and keep my caloric intake around 1500-1600. I promised to eat a few veggies too (gulp). That’s really the test right there.

It's a starting place
It’s a starting place

Here’s my scan. It’s horrible, I know, but remember I’m laying down and everything flattens out. Okay, it looks awful. Don’t judge. You have NO idea how hard this is to post. I keep telling myself it’s just a starting point. We can compare the next one in three months.

It’s time to burn some fat, people!! (I almost left out that comma, and that could have been tragic!) It starts tonight with a hike with a hubby and a chubby Weimeraner.

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