Pregnancy Weight Gain Calculator
Pregnancy weight gain calculator: check if your gain fits your week of pregnancy, based on your pre-pregnancy BMI and IOM ranges, for one baby or twins.
Written by HealthSensibly Editorial TeamReviewed by the HealthSensibly editorial teamUpdated
Healthy pregnancy weight gain, by starting BMI
How much you should put on depends on your body mass index (BMI) from before you were pregnant. The ranges below are from 2009 guidance issued in the US by the Institute of Medicine (the IOM, renamed the National Academy of Medicine), which ACOG and many doctors around the world follow. In the first trimester most women add just 0.5–2 kg, then gain at a fairly even weekly pace as shown.
| Pre-pregnancy BMI | Total gain (single baby) | Weekly gain, 2nd & 3rd trimester | Total gain (twins) |
|---|---|---|---|
| Underweight (below 18.5) | 12.5–18 kg (28–40 lb) | 0.44–0.58 kg (1–1.3 lb) | No set range — check with your doctor |
| Healthy (18.5–24.9) | 11.5–16 kg (25–35 lb) | 0.35–0.50 kg (0.8–1 lb) | 17–25 kg (37–54 lb) |
| Overweight (25–29.9) | 7–11.5 kg (15–25 lb) | 0.23–0.33 kg (0.5–0.7 lb) | 14–23 kg (31–50 lb) |
| Obese (30 or more) | 5–9 kg (11–20 lb) | 0.17–0.27 kg (0.4–0.6 lb) | 11–19 kg (25–42 lb) |
For every week, the tool plots a target band — 0.5–2 kg by week 13, then climbing evenly to the full range at 40 weeks — and marks your current gain on it.
What the extra kilos are made of
By full term the gain breaks down roughly as: placenta 0.7 kg, baby 3–3.5 kg, larger womb 1 kg, amniotic fluid 0.8 kg, breast tissue 0.5 kg, added blood volume 1.5 kg, extra body fluid 1.5 kg and fat stores 2.5–3.5 kg.
Off track in either direction?
- Gaining too little may increase the chance of a small baby or a premature birth.
- Gaining too much may increase the chance of gestational diabetes, raised blood pressure, a caesarean birth and weight that lingers afterwards.
- Pregnancy is not the time to diet — raise it with your doctor and eat well using a balanced pregnancy diet plan.
For South Asian women: the IOM figures rely on the usual BMI bands. Some Indian doctors apply lower cut-offs for Asian women (overweight starting at 23), so check with your own doctor which range suits you.
Common questions
What is normal for the first three months?
Generally a total of just 0.5–2 kg (1–4.5 lb). Plenty of women gain less, or drop a little weight because of morning sickness, and that is usually not a concern.
How many kilograms a week is typical later on?
From the second trimester onwards, roughly 0.35–0.5 kg (0.8–1 lb) per week if you started at a healthy BMI — a bit less if your BMI was higher and a bit more if it was lower.
I seem to be gaining quickly — what should I do?
Do not try to lose weight. Review portion sizes, sweet drinks and snacks, keep walking regularly, and bring it up at your next antenatal appointment.
Do the ranges change for twins?
Yes. Twin pregnancies have higher totals for healthy, overweight and obese starting BMIs; for an underweight start there is no set range, so ask your doctor.
References: IOM 2009: Weight gain during pregnancy · ACOG: Weight gain during pregnancy
Checked against the sources listed above. This is general health information and not medical advice — please ask your doctor or a registered dietitian what suits you.
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