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Expected Weight Loss From Gastric Bypass – Calculator

OC Staff Calculators, Featured, Gastric Bypass, Weight Loss Surgeries

Gastric bypass surgery will make you lose weight. I’m not aware of anyone who has had the surgery and not lost some weight. So the question is not if will you lose weight. Instead, how much weight will you lose?

How Much Weight Will I Lose?

The amount of weight you will lose depends on a number of factors. These factors include, diet, exercise, lifestyle, and your overall commitment to changing old habits. The size the surgeon makes your stomach and the length of your roux limb can make a small difference in weight loss but most of the time these surgical differences are minor. And today, most surgeons have very similar techniques when they perform gastric bypass surgery further minimizing surgical differences.

But let’s assume that you do everything right after surgery. You’ve changed your diet (gastric bypass forces some dietary changes, this is why gastric bypass creates more weight loss than most other procedures), you’re exercising regularly and you make an effort to sit less and be active more. How much will you weigh when all is said and done?

Average Excess Weight Loss With Gastric Bypass Surgery

Before we make any calculations, let’s look at the average weight loss from gastric bypass surgery. Because different people have different heights and weights and therefore different body mass index’s, we cannot measure expected weight loss in pounds. Someone who is 6 foot 2 and 400 lbs will lose a different amount of weight than someone who is 5 foot 4 and 220 lbs. But both of these patients will lose a similar percent of their excess weight.

Example Weight Loss

Patient 1 is 6 foot 2 and 400 lbs:

  • Patient 1’s ideal weight is 194.7 lbs.
  • Patient 1 has 205.3 lbs of excess weight.
  • He loses 65% of his excess weight, 133 lbs.
  • His new weight is 266 lbs 2 years after surgery.

Patient 2 is 5 foot 4 and 250 lbs.

  • Patient 2’s ideal weight is 145.6 lbs.
  • Patient 2 has 104.4 lbs of excess weight.
  • She loses 65% of her excess weight, 68 lbs.
  • Her new weight is 182 lbs, 2 years after surgery.

You can see how patient 1 lost 133 lbs and patient 2 lost 68 lbs but both of them lost the same percent of their excess weight. This is why we measure average weight loss after weight loss surgery as a percentage of excess weight.

On average gastric bypass patients lose about 70% (Bariatric Surgery, A Systemic Review and Meta Analysis, 2004) of their excess weight. To simplify, 70% is a good number to use when figuring your expected weight loss after gastric bypass.

How To Calculate Your Expected Weight Loss After Gastric Bypass

You will need a few numbers to get started calculating your expected weight loss. Follow steps 1 through 4 and you should have your expected weight loss calculated in just a few minutes.

1. What is your ideal weight?

There are a few common ways to calculate ideal weight. This calculator shows your ideal weight for all of the different methods to determine this number. I typically use the largest number, which is usually the high body mass Index number.

2. How much excess weight do you have to lose?

Current Weight – Ideal Weight = Excess Weight

3. How to calculate your expected weight loss:

Excess Weight x .70 = Expected Weight Loss

4. How to calculate your new weight:

Current Weight – Expected Weight Loss = New Weight After Surgery

Use Our Calculator

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Regardless of which weight loss surgery you choose, you can expect to lose a certain amount of weight from bariatric surgery. This calculator will tell you how much weight you can expect to lose from each bariatric procedure and what you can expect to weigh two years after surgery.

The calculations are based on average weight loss per procedure. To lose the average amount of weight, you’ll need to follow your surgeon’s pre-operative and post-operative guidelines.

Long term diet and exercise changes along with other habit changes can lead to weight loss that exceeds the averages used in these calculations.

Keep In Mind

Keep in mind that 70% is an average. There are people who lose less and some that lose much more. Ultimately, success from gastric bypass comes from setting the proper expectations, making a decision to change your habits and sticking to that decision.

If your number seems lower than expected, do not get upset. People are surprised that they cannot expect to go from 250 lbs down to 120 lbs from surgery alone. Gastric bypass is not a magic bullet, but it will get your weight down to something more manageable. Once your weight drops, it becomes easier to exercise, stay on your feet longer, enjoy life and continue to lose more weight.

The hardest part is losing the first 50 lbs of weight. Once you start to notice results you will be motivated to lose more, eat healthier, brag to your friends, and show off your amazing progress. Best of luck!


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