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Pregnancy Weight Gain Calculator (IOM Guidelines)
How much to gain in pregnancy: recommended weight gain by the IOM ranges based on your pre-pregnancy BMI, the weekly pace, and expected gain by your current week.
Updated: September 14, 2026 · 🔒 Your data never leaves your browser
Recommended pregnancy weight gain depends on your weight before pregnancy: about 11.5–16 kg at a normal BMI, 7–11.5 kg if overweight, and 12.5–18 kg if underweight. Enter your pre-pregnancy weight and height — the calculator finds your IOM range, shows the second- and third-trimester pace, and, if you add your week, the expected gain by now.
Pre-pregnancy BMI: 22.8 · normal
Recommended total gain
11.5–16 kg
Rate in 2nd–3rd trimester
0.4–0.5 kg/wk
IOM/NAM 2009 ranges for a singleton pregnancy. This is a guide, not a target to stress over: your actual gain and its pace are followed by your doctor, and ranges are higher for twins or multiples. A sharp jump — or no gain at all — is a reason to talk to a professional, not to force the number.
What the range depends on
The key factor is your pre-pregnancy BMI. The higher it is, the lower the recommended gain: a body with fat reserves doesn't need to add as much as one that's underweight. So there's no single "number of kilos" — there's a range for your starting weight.
| Pre-pregnancy BMI | Category | Recommended gain |
|---|---|---|
| below 18.5 | Underweight | 12.5–18 kg |
| 18.5–24.9 | Normal | 11.5–16 kg |
| 25.0–29.9 | Overweight | 7–11.5 kg |
| 30 and above | Obesity | 5–9 kg |
Pace by trimester
Gain is uneven. The first trimester adds almost nothing (0.5–2 kg total, and with nausea the scale sometimes dips). Most gain lands in the second and third trimesters and is roughly linear:
| Pre-pregnancy BMI | Rate in 2nd–3rd trimester |
|---|---|
| Underweight | 0.44–0.58 kg/wk |
| Normal | 0.35–0.50 kg/wk |
| Overweight | 0.23–0.33 kg/wk |
| Obesity | 0.17–0.27 kg/wk |
Читайте также: BMI and Body Composition: What It Shows and What It Misses
What the gained weight is made of
The gain is far from all fat, which is why it can't all come off at once after birth:
If you're outside the range
A one-off swing isn't a problem. But a consistent move outside the range is worth raising with your doctor: excessive gain is linked to gestational diabetes, a large baby and high blood pressure, while too little is linked to low birth weight. The goal is a healthy trend under supervision, not an exact number on the scale.
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FAQ
How much weight gain is normal in pregnancy?+
By the IOM/NAM guidelines it depends on your pre-pregnancy BMI: underweight (BMI < 18.5) 12.5–18 kg, normal (18.5–24.9) 11.5–16 kg, overweight (25–29.9) 7–11.5 kg, obese (≥ 30) 5–9 kg. These are ranges for a singleton pregnancy; twins are higher.
How is the gain spread across trimesters?+
The first trimester adds little — usually 0.5–2 kg over the whole three months. Most gain happens in the second and third trimesters: about 0.35–0.5 kg per week at a normal BMI, less if overweight. The calculator shows both the total range and the weekly pace.
What is the gained weight made of?+
It's not just fat. Roughly: baby 3–3.5 kg, placenta and amniotic fluid ~1.5 kg, larger uterus and breasts ~1–2 kg, extra blood and fluid ~2–3 kg, fat stores ~2–4 kg. That's why it doesn't all come off at once after birth — some leaves gradually.
What if I gain more or less than the range?+
A one-off swing is no cause for panic, but a consistent move outside the range is worth discussing with your doctor: both excessive gain (gestational diabetes, a large baby, high blood pressure) and too little (low birth weight) matter. The goal is a healthy trend under supervision, not a perfect number.
Is the range the same for twins?+
No. Multiple pregnancies have higher recommended gain: the IOM suggests roughly 17–25 kg for twins at a normal BMI. This calculator is for a singleton pregnancy; for twins follow your doctor's advice.
References
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