How to Calculate and Interpret a UBW

In developed countries, obesity is becoming an increasingly prevalent condition 1. It can lead to hypertension (high blood pressure), heart disease, stroke, cancer, diabetes and other serious health problems. Conversely, malnourishment is also a grave health risk, particularly in the developing world. The significance of weight gain or loss is related to a person's usual body weight (UBW), which is defined as that person's most frequent body weight. For example, a weight change of 12 pounds in one month would be considered significant for someone of low or average UBW but would not be significant for an obese person 2.

How to Calculate Percent UBW

Use past weight measurements and/or medical records to determine your most frequent body weight. This is your UBW.

Weigh yourself to determine your current body weight. Try to weigh yourself under the same conditions (e.g., fasting or after a meal, with or without shoes) under which your UBW weight measurements were taken.

Perform the following calculation in order to determine your percent UBW: percent UBW = current body weight/UBW x 100

Significance of Percent UBW

Perform the following calculation in order to determine your percent weight change: percent weight change = percent UBW - 100

Determine the duration of your weight gain or loss, i.e., the amount of time since your weight has consistently been close to your UBW 12. Ideally, this duration should be between one week and six months.

Characterize your percent weight change as being moderate, significant or severe according to the following guidelines:

One week---moderate: less than 1 percent; significant: 1 to 2 percent; severe: more than 2 percent;

One month---moderate: less than 5 percent; significant: 5 percent; severe: more than 5 percent;

Three months---moderate: less than 7.5 percent; significant: 7.5 percent; severe: more than 7.5 percent;

Six months---moderate: less than 10 percent; significant: 10 percent; severe: more than 10% percent.


Weight measurements should be adjusted for swelling, dehydration or pregnancy.


Consult a doctor before attempting to gain or lose a significant amount of weight.

Consult a doctor immediately if you have involuntarily gained or lost a significant amount of weight.

Percent weight changes characterized as moderate could be significant for individuals with special circumstances or for individuals with consecutive periods of weight change.