See the recommended weight gain range for your pregnancy based on your pre-pregnancy BMI, following IOM (Institute of Medicine) guidelines. Track expected weight gain by trimester and week.
Healthy pregnancy weight gain follows guidelines established by the Institute of Medicine (now National Academy of Medicine) based on pre-pregnancy BMI. The guidelines exist because weight gain that's too low can lead to preterm birth and low birth weight, while excessive gain increases risks of gestational diabetes, high blood pressure, complicated delivery, and difficulty losing weight postpartum. The recommendations are ranges (not single targets) and individual patterns vary substantially.
The IOM 2009 guidelines (updated incorporating modern obstetric data) recommend: - Underweight (BMI <18.5): 28-40 lbs total gain - Normal weight (BMI 18.5-24.9): 25-35 lbs total gain - Overweight (BMI 25-29.9): 15-25 lbs total gain - Obese (BMI 30+): 11-20 lbs total gain
For twin pregnancies: significantly higher (37-54 lbs typical depending on starting BMI). Triplet+ pregnancies have separate guidance.
This calculator computes your pre-pregnancy BMI, identifies your recommended weight gain range based on IOM guidelines, and projects expected weight at any given week. Use it for healthy gain tracking, conversations with your obstetrician, and identifying whether your trajectory is on track. Important: actual recommended gain for your specific situation should be confirmed with your obstetrician, who knows your medical history and any pregnancy-specific factors (gestational diabetes, hypertension, multiples, etc.).
145 lbs pre-pregnancy, 5'5". BMI 24.1 (normal weight). Recommended total: 25-35 lbs. At week 30: expected weight 145 + 3 + 17 = 165 lbs (about 20 lbs gained). On-track pattern: moderate first-trimester gain (often little to none with nausea), steady 1 lb/week through second and third trimesters. Most normal-weight women fall within the 25-35 lb range; outside this range warrants conversation with provider.
185 lbs pre-pregnancy, 5'4". BMI 31.8 (obese). Recommended total: 11-20 lbs. At week 30: expected gain ~10-12 lbs (slower rate). Lower total gain recommendation reflects evidence that women starting overweight or obese have healthier pregnancies and infants with more modest weight gain. Counterintuitively, women with high pre-pregnancy BMI sometimes lose weight in the first trimester (which is acceptable if not excessive). Postpartum weight loss is often easier with modest pregnancy weight gain.
135 lbs pre-pregnancy, 5'6". BMI 21.8 (normal weight). Singleton recommendation: 25-35 lbs. Twin recommendation: 37-54 lbs. Twins require substantially more weight gain to support two babies. The IOM provisional guidance recognizes the higher metabolic demand. Twin pregnancies also typically deliver earlier (37-38 weeks vs. 39-40 for singleton), compressing the gain timeline. Twin pregnancies should be managed with a maternal-fetal medicine specialist or experienced obstetrician given higher complication rates.
Use this calculator during prenatal planning, throughout pregnancy to track gain pattern, before pregnancy if planning conception and assessing weight optimization.
This is a planning tool. Always follow your obstetrician's specific guidance — they consider factors beyond IOM guidelines (medical conditions, prior pregnancy history, current symptoms).
Pair with: due-date, BMI calculator (for pre-pregnancy BMI), calorie calculator (pregnancy calorie needs are higher).
A few important pregnancy weight gain principles:
1. **Range, not target.** IOM guidelines are ranges. Being at the lower or upper end is fine; meaningfully outside the range warrants discussion.
2. **First trimester gain often minimal.** Nausea, food aversions, and morning sickness often cause minimal weight gain or even loss in the first trimester. This is normal for many women.
3. **Most gain in second/third trimester.** About 1 lb/week is typical for normal-weight women in weeks 13-40. Steady gain is the goal.
4. **Track trends, not daily fluctuations.** Daily weight varies 1-3 lbs from fluid alone. Weekly weigh-ins or trends over 2-4 weeks are more meaningful.
5. **Quality of weight matters.** Adequate protein, healthy fats, fruits/vegetables produce healthier weight gain than processed/junk food gain. Same scale weight, different impact on baby and mother.
6. **Postpartum loss varies.** About 15-20 lbs typically lost in the first 2 weeks (baby, placenta, amniotic fluid, blood volume normalization). Remaining gain takes 6-12 months to lose with proper diet and gradual return to activity. Don't expect immediate return to pre-pregnancy weight.
Estimate your pregnancy due date from your last menstrual period.
Calculate your Body Mass Index from height and weight.
Calculate daily calorie needs based on age, weight, height, and activity level.
Calculate target heart rate training zones by age using the Karvonen method.
Predict a child's adult height from parents' heights using the mid-parent method.
Convert A1C percentage to estimated average blood glucose (eAG) and vice versa.
Recommended Total Gain
25-35 lbs
Expected at Current Week
7.7-13.3 lbs
BMI Category
Normal Weight
Pre-pregnancy BMI: 23.3
Weekly Rate (2nd/3rd tri)
~1 lb/week
| Trimester | Min Gain (lbs) | Max Gain (lbs) |
|---|---|---|
| First (1-13) | 1 | 5 |
| Second (14-26) | 11 | 16 |
| Third (27-40) | 11 | 16 |