Free Pregnancy Tool
Compare weight gained so far with the typical range for this week, based on pre-pregnancy BMI. Private - nothing leaves this page.
Please check the values entered.
| Pre-pregnancy BMI | Range | One baby | Twins |
|---|---|---|---|
| Below 18.5 | Underweight | 12.5–18 kg (28–40 lb) | No guideline |
| 18.5–24.9 | Healthy weight | 11.5–16 kg (25–35 lb) | 16.8–24.5 kg (37–54 lb) |
| 25–29.9 | Overweight | 7–11.5 kg (15–25 lb) | 14.1–22.7 kg (31–50 lb) |
| 30 and above | Obese | 5–9 kg (11–20 lb) | 11.3–19.1 kg (25–42 lb) |
US Institute of Medicine (2009) guidance. Twin ranges are provisional. The UK has no formal weight gain target - NICE focuses on a balanced diet and staying active.
It compares how much weight has been gained so far with the range that's typical for that week of pregnancy. The range depends on pre-pregnancy BMI, because people who start at a lower weight are usually advised to gain more, and people who start higher, less.
The calculator works out pre-pregnancy BMI from height and weight, then looks up the total gain recommended by the US Institute of Medicine. Around 0.5-2 kg is typical in the first trimester, so that's spread over weeks 1-13. The rest of the range is spread evenly from week 14 to week 40. Twins use the IOM's provisional ranges.
Weight in pregnancy can be a sensitive subject. Most of it is the baby, placenta, fluid, extra blood, and the reserves the body builds for birth and feeding. Knowing what's typical helps you be reassuring rather than commenting - and spot when it's worth mentioning something to the midwife.
FAQ
What's typical, where the weight goes, and when it's worth talking to the midwife.
It depends on pre-pregnancy BMI. The US Institute of Medicine recommends 11.5-16 kg (25-35 lb) for a healthy BMI, 12.5-18 kg if underweight, 7-11.5 kg if overweight, and 5-9 kg if obese. The NHS notes most women gain 10-12.5 kg, and there's no formal UK target.
Usually only 0.5-2 kg in the first trimester. Most weight comes in the second and third trimesters - roughly 0.4-0.5 kg a week for someone who started at a healthy weight, and less for someone who started above it.
By term, around 3.4 kg is the baby, 0.7 kg the placenta, 0.8 kg amniotic fluid, 0.9 kg the womb, 1.2-1.5 kg extra blood, 1.2-1.5 kg extra fluid, 0.4 kg breast tissue, and 2.7-3.6 kg fat stores for birth and breastfeeding.
Yes, some weight loss in the first trimester is common because of nausea and sickness, and it's usually regained later. If sickness is severe or she can't keep food or fluids down, contact a GP or midwife - it could be hyperemesis gravidarum.
The ranges are population guidelines, not targets. The overall trend matters more than one reading. Dieting isn't recommended in pregnancy. If gain is consistently outside the range - or there's sudden gain with swelling, headaches or vision changes - speak to the midwife.
Calculate pre-pregnancy BMI from height and weight, see the BMI range it falls in, and the weight gain usually recommended for it.
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