Pregnancy Weight Gain Calculator — How Much Should You Gain?
Calculate recommended pregnancy weight gain based on your pre-pregnancy BMI. Week-by-week targets, trimester breakdown, and when to talk to your doctor.
"Am I gaining too much? Too little?" is one of the most anxious questions during pregnancy. The answer depends almost entirely on your pre-pregnancy BMI, and the recommended ranges are wider than most people think. The CalcHub Pregnancy Weight Gain Calculator gives you personalized week-by-week targets.
Recommended Total Weight Gain (IOM Guidelines)
| Pre-Pregnancy BMI | Category | Recommended Gain (Singleton) | Recommended Gain (Twins) |
|---|---|---|---|
| Below 18.5 | Underweight | 12.5–18 kg (28–40 lbs) | — |
| 18.5–24.9 | Normal weight | 11.5–16 kg (25–35 lbs) | 17–25 kg (37–54 lbs) |
| 25.0–29.9 | Overweight | 7–11.5 kg (15–25 lbs) | 14–23 kg (31–50 lbs) |
| 30.0+ | Obese | 5–9 kg (11–20 lbs) | 11–19 kg (25–42 lbs) |
Where the Weight Actually Goes
At full term (~40 weeks), weight gain is distributed across:
| Component | Weight |
|---|---|
| Baby | 3.0–3.5 kg (6.5–8 lbs) |
| Placenta | 0.7 kg (1.5 lbs) |
| Amniotic fluid | 0.9 kg (2 lbs) |
| Uterus growth | 0.9 kg (2 lbs) |
| Breast tissue | 0.5–1.4 kg (1–3 lbs) |
| Increased blood volume | 1.4–1.8 kg (3–4 lbs) |
| Extra fluid | 1.4–2.3 kg (3–5 lbs) |
| Fat stores (energy for labor/breastfeeding) | 2.7–3.6 kg (6–8 lbs) |
| Total | ~11.5–16 kg (25–35 lbs) |
Trimester Breakdown
First Trimester (Weeks 1–13)
- Expected gain: 0.5–2 kg (1–4 lbs) total
- Some women lose weight due to morning sickness — this is normal
- The baby is tiny (about 30 grams by week 12)
- No "eating for two" — you don't need extra calories in the first trimester
Second Trimester (Weeks 14–27)
- Expected gain: ~0.5 kg (1 lb) per week
- This is when most weight gain occurs
- Extra calorie needs: ~340 calories/day above pre-pregnancy
- Baby grows from ~100g to ~900g
Third Trimester (Weeks 28–40)
- Expected gain: ~0.5 kg (1 lb) per week (may slow down near the end)
- Extra calorie needs: ~450 calories/day above pre-pregnancy
- Baby gains most of their birth weight in this trimester
- Weight may plateau or even drop slightly in the last 1–2 weeks
Week-by-Week Guide (Normal BMI, Singleton)
| Week | Cumulative Gain (kg) | Cumulative Gain (lbs) |
|---|---|---|
| 4 | 0 | 0 |
| 8 | 0.5 | 1 |
| 12 | 1.0–2.0 | 2–4 |
| 16 | 2.5–3.5 | 5–8 |
| 20 | 4.0–5.5 | 9–12 |
| 24 | 5.5–7.5 | 12–17 |
| 28 | 7.0–9.5 | 15–21 |
| 32 | 9.0–11.5 | 20–25 |
| 36 | 10.5–14.0 | 23–31 |
| 40 | 11.5–16.0 | 25–35 |
How to Use the Calculator
- Open the CalcHub Pregnancy Weight Gain Calculator
- Enter pre-pregnancy weight and height (for BMI calculation)
- Enter current week of pregnancy
- See: recommended total gain, current target, and whether you're on track
When to Be Concerned
| Situation | What to Do |
|---|---|
| Gaining much faster than recommended | Discuss with OB/GYN; may need dietary adjustments |
| Gaining much slower than recommended | Rule out nutritional deficiencies; may need to increase calorie-dense foods |
| Sudden weight gain (>1 kg/week in 3rd trimester) | Could indicate preeclampsia — contact doctor immediately |
| Weight loss after first trimester | Contact doctor to rule out complications |
| No weight gain by 20 weeks | Discuss with doctor |
Practical Tips
It's a range, not an exact number. Gaining 14 kg when the recommendation is 11.5–16 kg is perfectly fine. Don't stress about hitting a specific number weekly. Don't diet during pregnancy. Restricting calories can deprive the baby of essential nutrients. Focus on nutrient density, not calorie counting. The "eating for two" myth. You need approximately 0 extra calories in the first trimester, 340 extra in the second, and 450 extra in the third. That's roughly one extra meal, not double portions. Water weight fluctuates. Daily weight can swing 0.5–1 kg based on hydration, sodium intake, and fluid retention. Weigh yourself weekly under consistent conditions (morning, after bathroom, before eating).Will I lose the weight after delivery?
Most women lose 5–6 kg immediately after delivery (baby, placenta, amniotic fluid). Another 2–3 kg of fluid weight drops within the first week. The remaining weight typically comes off over 6–12 months, especially with breastfeeding (which burns 300–500 calories/day).
What if I was already overweight before pregnancy?
You still need to gain weight — just less. The guidelines for overweight women (BMI 25–29.9) are 7–11.5 kg total. Do not try to lose weight during pregnancy. Focus on nutritious food and staying active.
Does weight gain affect the baby's size?
Excessive weight gain is associated with larger babies (macrosomia), which can complicate delivery. Insufficient gain is associated with lower birth weight and preterm birth. Staying within the recommended range minimizes both risks.
Related Calculators
- BMI Calculator — calculate your pre-pregnancy BMI
- Pregnancy Due Date Calculator — estimate delivery date
- Calorie Calculator — daily calorie needs
- Conception Calculator — when did you conceive