Pregnancy Weight Gain Calculator guide
Pregnancy Weight Gain Calculator: How Much Weight Should I Gain?
Use our Pregnancy Weight Gain Calculator to see the typical healthy weight gain for your BMI, week by week, including for twins, with NHS advice.
By the AllCalculator editorial teamUpdated 15 October 20263 min read
Gaining weight in pregnancy is normal and healthy. Your baby, the placenta, extra blood and fluid, and the stores your body builds for breastfeeding all add up. But it's natural to wonder whether you're gaining too much or too little.
Our Pregnancy Weight Gain Calculator shows the typical range for your body mass index (BMI) and what you might expect by your current week. For your due date and key dates, see our main Pregnancy Calculator.
Remember: every pregnancy is different. These ranges are a guide, not a target, and your midwife is the best person to talk to about your own weight.
What the NHS says
There's no official UK target for weight gain in pregnancy. The NHS says most women gain between 10kg and 12.5kg (22lb to 28lb), mostly after week 20. Gaining much more or much less than usual can affect your health and your baby's, so your midwife may give you extra advice if your BMI was over 30 or under 18.5 before you got pregnant.
The NHS is also clear that pregnancy isn't the time to diet. Eating well and staying active is what matters.
Ranges by BMI
Many UK clinicians refer to guidelines from the US Institute of Medicine, published in 2009. These give a recommended range based on your BMI before pregnancy:
| BMI before pregnancy | Total gain (one baby) | Total gain (twins) |
|---|---|---|
| Under 18.5 (underweight) | 12.5 to 18 kg | No recommendation |
| 18.5 to 24.9 (healthy weight) | 11.5 to 16 kg | 17 to 25 kg |
| 25 to 29.9 (overweight) | 7 to 11.5 kg | 14 to 23 kg |
| 30 or over (obese) | 5 to 9 kg | 11 to 19 kg |
The twin ranges are described as provisional, because they're based on less research.
Weight gain isn't spread evenly. A typical pattern is around 0.5kg to 2kg in the first trimester, then a steadier gain each week from the second trimester onwards.
How to use the calculator (Pregnancy Weight Gain Calculator)
- Choose your units: kilograms and centimetres, or stones and feet.
- Enter your height and your weight before pregnancy.
- Optionally, enter your weight now.
- Enter how many weeks pregnant you are. Not sure? Our How Many Weeks Pregnant Calculator will tell you.
- Say whether you're expecting twins.
You'll see your pre-pregnancy BMI, the suggested total gain, the typical range by your current week and the usual weekly gain in the second and third trimesters. If you entered your current weight, you'll also see how much you've gained and how it compares.
A worked example
With the calculator's default settings, someone is 165cm tall, weighed 62kg before pregnancy and is 20 weeks pregnant:
- BMI before pregnancy: 62 ÷ (1.65 × 1.65) = 22.8, a healthy weight
- Suggested total gain: 11.5 to 16kg
- Typical gain by week 20: about 2.9 to 5.5kg
- From week 14, about 0.35 to 0.5kg a week
Where the weight goes
At full term, a typical pregnancy weight gain is made up of your baby, the placenta and amniotic fluid, a bigger womb and breasts, extra blood and fluid, and some fat stores for breastfeeding. Only part of it is fat, which is why gaining weight in pregnancy is necessary and healthy.
Frequently asked questions
How much weight should I gain in pregnancy?
Most women gain between 10kg and 12.5kg, according to the NHS. The right amount for you depends on your weight before pregnancy, so the calculator gives a range based on your BMI.
Is it OK to lose weight in early pregnancy?
Some people lose a little weight in the first trimester because of sickness. That's usually nothing to worry about, but speak to your midwife or GP if you're being sick a lot or can't keep food down.
Should I diet if I'm gaining too much?
No. The NHS advises against dieting in pregnancy. Focus on a balanced diet and regular activity, and ask your midwife for advice if you're concerned.
Do I need to eat for two?
No. You don't need extra calories in the first 6 months. In the last 3 months, you need only around 200 extra calories a day.
Weight gain is just one part of a healthy pregnancy. Use the Pregnancy Weight Gain Calculator as a guide, and keep track of your dates with the main Pregnancy Calculator.
Sources and further reading
- NHS: Weight gain in pregnancynhs.uk
- NHS: Have a healthy diet in pregnancynhs.uk
- National Academies: Weight Gain During Pregnancy (2009)nap.nationalacademies.org
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This guide is general information to help you understand your options. It isn't financial, tax, legal or building advice and doesn't take your personal circumstances into account. Figures were checked when the guide was last updated and can change, so confirm anything important with GOV.UK, HMRC, a regulated adviser or a qualified tradesperson.