UK Calculator Editorial · Calculator verified · Apr 2026

Pregnancy Weight Gain Calculator UK

NHS Recommended Pregnancy Weight Gain Guidelines

The NHS and NICE (National Institute for Health and Care Excellence) base pregnancy weight gain recommendations on your pre-pregnancy BMI. Gaining the right amount of weight helps your baby grow healthily while reducing risks for both mother and child.

Pre-pregnancy BMI	Category	Recommended Gain (kg)	Recommended Gain (lbs)
Under 18.5	Underweight	12.7–18.1 kg	28–40 lbs
18.5–24.9	Normal weight	11.3–15.9 kg	25–35 lbs
25.0–29.9	Overweight	6.8–11.3 kg	15–25 lbs
30.0 and above	Obese	5.0–9.1 kg	11–20 lbs
Any (twins)	Twin pregnancy	15.9–20.4 kg+	35–45 lbs+

Important: These are general guidelines. Always discuss your individual weight gain targets with your midwife or GP, as personal health history, height, and other factors matter.

How Weight Gain is Distributed in Pregnancy

Many women wonder where pregnancy weight actually goes. Here is a typical breakdown for a normal-weight woman gaining around 12.5 kg:

Baby3–4 kg

Placenta0.7 kg

Amniotic fluid0.9 kg

Uterus growth0.9 kg

Breast tissue0.9 kg

Increased blood volume1.5 kg

Fluid and tissue2.0 kg

Fat stores (energy for breastfeeding)2–3 kg

Weight Gain by Trimester

Weight gain is not evenly spread across pregnancy. The pattern matters as much as the total.

First Trimester (Weeks 1–12)

Total weight gain of just 1–2 kg is normal in the first trimester. The embryo is tiny, and much of the discomfort from nausea or morning sickness can actually make eating difficult. Some women lose a small amount of weight during this period, which is generally not a concern provided weight gain picks up in the second trimester.

Second Trimester (Weeks 13–26)

This is typically when appetite returns and weight gain accelerates. For normal-weight women, approximately 0.45 kg (1 lb) per week is typical. This is when the baby grows most rapidly and when you may first notice your bump becoming visible.

Third Trimester (Weeks 27–40)

Weight gain continues at a similar pace — roughly 0.45–0.5 kg per week. The baby is laying down fat stores, and your blood volume continues to increase. In the final 2–3 weeks, some women find their weight plateaus or even drops slightly as the baby drops into the pelvis.

Risks of Inadequate or Excessive Weight Gain

Too little weight gain:

Preterm birth
Low birth weight baby (under 2.5 kg)
Restricted fetal growth
Developmental delays
Breastfeeding difficulties

Too much weight gain:

Gestational diabetes
Pre-eclampsia
Large baby (macrosomia)
Higher caesarean section rate
Difficulty losing weight after birth
Back and joint pain

Twin Pregnancies and Weight Gain

Carrying twins requires significantly higher calorie intake and results in greater weight gain. The NHS and NICE guidelines for twin pregnancies are:

Normal weight (BMI 18.5–24.9): 16.8–24.5 kg
Overweight (BMI 25–29.9): 14.1–22.7 kg
Obese (BMI 30+): 11.3–19.1 kg

If you are expecting twins, you will be referred to a consultant obstetrician and will receive more frequent antenatal appointments to monitor weight and fetal growth.

When to Speak to Your Midwife About Weight

Contact your midwife or GP if:

You have lost more than 2 kg in the first trimester due to severe vomiting (hyperemesis gravidarum)
You are gaining weight significantly faster or slower than expected
You have a BMI over 30 and want personalised dietary guidance
You have a history of eating disorders
You are concerned about swelling (oedema) which can cause sudden weight increases

The NHS does not routinely weigh pregnant women at every appointment. If you have concerns, raise them directly — your midwife can refer you to a specialist obstetric dietitian.

Frequently Asked Questions

How much weight should I gain during pregnancy in the UK?

The NHS recommends weight gain based on your pre-pregnancy BMI. Underweight women (BMI under 18.5) should gain 12.7–18.1 kg; normal weight (18.5–24.9) 11.3–15.9 kg; overweight (25–29.9) 6.8–11.3 kg; obese (30+) 5–9.1 kg. These ranges are for singleton pregnancies and are based on NICE guidelines adopted across the UK.

How much weight should you gain in the first trimester?

In the first trimester (weeks 1–12) you should gain approximately 1–2 kg in total. This slow gain is completely normal — the baby is still the size of a lime at 12 weeks. Many women experience nausea, vomiting or food aversions that can make eating challenging.

How much weight should you gain per week in the second and third trimesters?

In the second and third trimesters, the NHS advises gaining roughly 0.45–0.5 kg per week for women of normal pre-pregnancy weight. Underweight women may need slightly more (up to 0.59 kg/week), while overweight women should aim for less (around 0.23–0.32 kg/week).

Where does the pregnancy weight come from?

Pregnancy weight is distributed across: baby (3–4 kg), placenta (0.7 kg), amniotic fluid (0.9 kg), uterus enlargement (0.9 kg), breast tissue increase (0.9 kg), additional blood volume (1.5 kg), and extra tissue fluid and fat stores (2–3 kg). The majority of weight is water-based and will be lost after birth.

Is it dangerous to gain too much weight in pregnancy?

Gaining too much weight increases the risk of gestational diabetes, pre-eclampsia (high blood pressure), a large baby requiring caesarean delivery, and difficulty returning to pre-pregnancy weight. However, weight management during pregnancy should never involve calorie restriction without medical supervision.

What if I am not gaining enough weight during pregnancy?

Insufficient weight gain may restrict fetal growth (intrauterine growth restriction), increase the risk of preterm birth, and result in a low-birth-weight baby. Contact your midwife if you are losing weight unexpectedly or gaining significantly less than expected for your BMI category.

How much weight do you gain with twins?

Twin pregnancies require higher weight gain: normal weight women should gain 16.8–24.5 kg; overweight women 14.1–22.7 kg; obese women 11.3–19.1 kg. Your consultant will monitor you closely throughout a twin pregnancy.

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Last updated: February 2026. This calculator provides general guidance only and does not replace professional medical advice. Always consult your midwife or GP for personalised recommendations. Written by Mustafa Bilgic.

Pregnancy Weight Gain Calculator

Step 1: Calculate Your Pre-Pregnancy BMI

Height (cm)

Pre-Pregnancy Weight (kg)

Step 2: Get Your Weight Gain Recommendations

Pre-Pregnancy BMI

Pregnancy Type

Current Week of Pregnancy (optional)

Weight Gained So Far in kg (optional)

Pregnancy Planning in the UK

Pregnancy is an exciting time, and being well-informed helps you prepare for every stage. The NHS provides comprehensive free maternity care throughout pregnancy, including regular check-ups, scans, and specialist support where needed.

Your first appointment with a midwife, known as the booking appointment, usually happens between 8 and 12 weeks. You will receive a dating scan at around 12 weeks and an anomaly scan at around 20 weeks. Throughout your pregnancy, regular appointments monitor both your health and your baby's development.

Key Milestones to Know

First trimester — weeks 1-12, including booking appointment and dating scan
Second trimester — weeks 13-27, including the anomaly scan at week 20
Third trimester — weeks 28-40, with more frequent monitoring
Maternity leave — can start from 11 weeks before due date, statutory pay for up to 39 weeks
Birth plan — discuss your preferences with your midwife in advance

This calculator helps you track important dates and milestones throughout your pregnancy. All information is based on NHS guidelines and standard pregnancy timelines. For specific medical advice, always consult your midwife or GP.

Official Sources

Data verified against official UK government sources. Last checked April 2026.