How is BMI calculated?

BMI is calculated as weight in kilograms divided by height in meters squared.

How much weight should be gained during a singleton pregnancy?

Recommended total gain depends on pre-pregnancy BMI: 28 to 40 lb for underweight, 25 to 35 lb for normal weight, 15 to 25 lb for overweight, and 11 to 20 lb for obesity.

What can cause excessive pregnancy weight gain?

Excessive gain may reflect calorie intake above needs, sugar-sweetened beverages, reduced activity, fluid retention or edema, medications, endocrine disease, or inaccurate baseline weight. Rapid gain should prompt assessment for edema and hypertensive disorders when clinically indicated.

What can cause insufficient pregnancy weight gain?

Insufficient gain may reflect nausea and vomiting, food insecurity, restrictive eating, gastrointestinal disease, medication effects, substance use, depression, or inaccurate baseline weight. It may warrant nutrition review and fetal growth assessment depending on gestational age and clinical context.

Body Mass Index (BMI) and Pregnancy Weight Gain Calculator

Enter weight and height for live BMI results. Add pre-pregnancy weight and gestational age to estimate pregnancy weight-gain adequacy using IOM/ACOG ranges for singleton pregnancy and provisional total ranges for twins.

No submit is required. Results update as values are entered.

Calculator

Required measurementsLive result

Current weight

Sex for IBW

Height

Pregnancy weight gainOptional

Pregnancy type

Pre-pregnancy weight

Gestational age

Days

Show graph

Leave unchecked for a cleaner mobile result. The graph can be opened when visual counseling is helpful.

Enter current weight and height to begin.

Results

BMI

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Enter weight and height

IBW

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Devine formula

Adjusted BW

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If clinically appropriate

Results will update automatically.

Pregnancy weight-gain result

Pre-pregnancy BMI

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Current gain

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Expected by GA

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Approximate range

Total target

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Pregnancy result will appear after optional fields are completed.

Weight-gain graph

Recommended rangeEntered current gain

The visual grid is an approximate pacing aid. Formal recommendations are based primarily on total gestational weight gain and average second/third-trimester rates.

Where does pregnancy weight gain go?

Illustrative singleton pregnancy weight-gain distribution. Individual values vary with gestational age, baseline BMI, edema, fetal growth, and plurality.

Clinical context for abnormal pregnancy weight gain

This section appears only when pregnancy weight gain is above or below the displayed expected range.

BMI category tables

BMI	CDC adult category
<18.5	Underweight
18.5 to <25	Healthy weight
25 to <30	Overweight
30 to <35	Class 1 obesity
35 to <40	Class 2 obesity
≥40	Class 3 obesity / severe obesity

WHO obesity-related health-risk classification

BMI	WHO nutritional status	WHO obesity-related comorbidity risk
<18.5	Underweight	Low for obesity-related comorbidity, but other clinical risk may be increased.
18.5–24.9	Normal range	Average risk.
25.0–29.9	Pre-obese / overweight	Increased risk.
30.0–34.9	Obesity class I	Moderate risk.
35.0–39.9	Obesity class II	Severe risk.
≥40	Obesity class III	Very severe risk.

IOM/ACOG pregnancy weight-gain recommendations

Singleton pregnancy

Pre-pregnancy BMI	Total singleton gain	Approximate 2nd–3rd trimester rate
Underweight <18.5	28–40 lb	1.0–1.3 lb/week
Normal 18.5–24.9	25–35 lb	0.8–1.0 lb/week
Overweight 25.0–29.9	15–25 lb	0.5–0.7 lb/week
Obesity ≥30	11–20 lb	0.4–0.6 lb/week

Twin pregnancy

Pre-pregnancy BMI	Provisional total twin gain	Clinical note
Underweight <18.5	Not specified	IOM/ACOG do not provide a specific provisional twin range for underweight BMI.
Normal 18.5–24.9	37–54 lb	Provisional range.
Overweight 25.0–29.9	31–50 lb	Provisional range.
Obesity ≥30	25–42 lb	Provisional range.

For twins, the graph is a pacing aid based on provisional total IOM ranges; official week-specific twin targets are less well established.

Clinical summary

Copy/paste summary for documentation.

BMI summary will appear after calculation.

Use notes

BMI is a screening measure and does not directly measure body composition or metabolic risk. Adjusted body weight is displayed for protocols where it is clinically appropriate; confirm medication-specific or institutional formulas before use.

Pregnancy weight-gain adequacy is approximate and should be interpreted with maternal condition, edema, fetal growth, nutrition history, and comorbidities.

References

Centers for Disease Control and Prevention. Adult BMI Categories. Updated 2024. CDC BMI categories.
American College of Obstetricians and Gynecologists. Committee Opinion No. 548: Weight Gain During Pregnancy. Obstet Gynecol. 2013;121:210–212. Reaffirmed by ACOG. ACOG guidance.
Institute of Medicine and National Research Council. Weight Gain During Pregnancy: Reexamining the Guidelines. Washington, DC: National Academies Press; 2009. National Academies report.
Rasmussen KM, Catalano PM, Yaktine AL. New guidelines for weight gain during pregnancy: what obstetrician/gynecologists should know. Curr Opin Obstet Gynecol. 2009;21:521–526. Full text.

Disclaimer: All calculations should be confirmed before clinical use. This calculator is for education and documentation support and does not replace clinical judgment.