Pregnancy Weight Gain Calculator
See the general reference range for pregnancy weight gain based on your pre-pregnancy BMI, and how your gain so far compares — for singleton or twin pregnancies.
Your Weight Gain Reference Guide
NICE (NG247, 2025) says there is currently insufficient evidence to define an optimal total or trimester-specific amount of weight change in pregnancy, and advises focusing on healthy eating and physical activity rather than a weight-gain number. Where someone wants to monitor their weight, NICE notes healthcare professionals can refer to estimated healthy weight change by pre-pregnancy BMI. This calculator uses the 2009 US Institute of Medicine (IOM) guidelines as a published reference framework.
Pregnancy Weight Gain Calculator UK
Our Pregnancy Weight Gain Calculator shows the general reference range for weight gain during pregnancy, based on your pre-pregnancy BMI, for both singleton and twin pregnancies. Current UK guidance does not set an evidence-based numeric target for pregnancy weight gain, so like most calculators of this kind, ours uses the widely referenced US Institute of Medicine (National Academies) guidelines. These figures are population-level reference ranges, not personal goals — every pregnancy is different, and pregnancy is never the right time to diet.
How Much Weight Should I Gain in Pregnancy?
The NHS notes that most pregnant women gain between 10 kg and 12.5 kg (22 lb to 28 lb) overall, with most of that gain happening after 20 weeks — but this describes what typically happens rather than a formal target to aim for. NICE’s 2025 guideline on maternal and child nutrition (NG247) goes further: it states there is currently insufficient evidence to define an optimal total or trimester-specific amount of weight change in pregnancy, and advises that healthcare professionals focus advice on starting or maintaining a healthy diet and physical activity, rather than a weight-gain number. NICE adds that, if someone wants to monitor their weight change, healthcare professionals can refer to the estimated healthy total weight change according to pre-pregnancy BMI. This calculator uses the 2009 US Institute of Medicine (IOM) guidelines as a published reference framework.
| Pre-Pregnancy BMI Category | Total Gain (Singleton) | Total Gain (Twins, provisional) |
|---|---|---|
| Underweight (below 18.5) | 12.5–18 kg (28–40 lb) | Not established by the IOM |
| Healthy weight (18.5–24.9) | 11.5–16 kg (25–35 lb) | 16.8–24.5 kg (37–54 lb) |
| Overweight (25–29.9) | 7–11.5 kg (15–25 lb) | 14.1–22.7 kg (31–50 lb) |
| Obese (30 and above) | 5–9 kg (11–20 lb) | 11.3–19.1 kg (25–42 lb) |
How to Use the Pregnancy Weight Gain Calculator
- Choose your units — metric (kg/cm) or imperial (stone and pounds/feet and inches).
- Select singleton or twins to match your pregnancy.
- Enter your pre-pregnancy weight and height so we can calculate your pre-pregnancy BMI.
- Optionally enter your current stage — either the week directly, or your estimated due date from our Pregnancy Due Date Calculator — to see the published reference gain-to-date.
- Optionally enter your current weight to see how your own gain so far compares to the typical range.
Understanding the Pattern of Weight Gain
Weight gain in pregnancy isn’t spread evenly. In the first trimester (up to around 13 weeks), total gain is typically small — the IOM gives a figure of about 0.5 to 2 kg (1 to 4 lb) across the whole trimester, regardless of your starting BMI, rather than a week-by-week amount. Most weight gain happens in the second and third trimesters, at a published reference weekly rate that depends on your pre-pregnancy BMI category: roughly 0.44–0.58 kg a week if you started underweight, 0.35–0.50 kg a week at a healthy weight, 0.23–0.33 kg a week if overweight, and 0.17–0.27 kg a week if obese. These are general reference figures, not personal targets — week-to-week gain naturally varies, and NICE itself notes there isn’t enough evidence to say what the optimal amount is in any given week or trimester.
Extra Energy Needs in Pregnancy (NHS Guidance)
Contrary to the “eating for two” myth, the NHS advises that most people don’t need any extra calories in the first two trimesters. In the final three months of pregnancy, the NHS suggests around 200 extra calories a day — about the same as two slices of wholemeal toast with margarine. Eating significantly more than this doesn’t make you or your baby healthier, and may increase the risk of complications such as gestational diabetes. Focus on a balanced diet rather than counting extra calories precisely.
What If My Weight Gain Is Outside the Typical Range?
Being below or above the reference range shown here doesn’t automatically mean something is wrong — many healthy pregnancies fall outside it, and factors like morning sickness, existing health conditions, or simply individual variation all play a part. If your gain is consistently low, your midwife may check that you and your baby are getting everything you need. If it’s consistently high, the advice is to focus on a healthy, balanced diet and staying active — never to restrict food or actively try to lose weight during pregnancy without medical supervision. Speak to your midwife or GP about what’s appropriate for you specifically.
A Note on BMI in Pregnancy
Your pre-pregnancy BMI is used here only to select the right reference range — it isn’t a judgement on your health. BMI is a general screening measure and has known limitations; for example, some UK guidance uses lower BMI thresholds to flag increased health risks for people of South Asian, Chinese, other Asian, Middle Eastern, Black African or African-Caribbean family backgrounds. Your midwife will calculate your BMI at your booking appointment and can advise if any of this applies to you.
Frequently Asked Questions
Is there an official UK guideline for pregnancy weight gain?
No. NICE’s 2025 guideline on maternal and child nutrition (NG247) states there is currently insufficient evidence to define an optimal total or trimester-specific amount of weight change in pregnancy, so there’s no UK evidence-based target range. NICE advises focusing on healthy eating and physical activity, and notes that healthcare professionals can refer to estimated healthy total weight change by pre-pregnancy BMI if someone wants to monitor their weight. This calculator uses the 2009 US Institute of Medicine (IOM) guidelines as a published reference framework.
How is the recommended weight gain range worked out?
The IOM guidelines set a recommended total weight gain range based on your pre-pregnancy BMI category — underweight, healthy weight, overweight or obese — with lower BMI categories generally recommended a higher total gain, and higher BMI categories a lower one. For singleton pregnancies, the guidelines also give a recommended weekly rate of gain for the second and third trimesters.
Is the recommended range different for twins?
Yes. The IOM publishes separate, provisional reference ranges for total weight gain in twin pregnancies at a healthy weight, overweight and obese pre-pregnancy BMI. There wasn’t enough evidence for the IOM to publish a guideline for twin pregnancies starting from an underweight BMI, or a specific weekly rate of gain for any twin BMI category — your midwife can advise on what’s appropriate for you.
What if my weight gain is below or above the typical range?
It doesn’t automatically mean something is wrong — many healthy pregnancies sit outside these general ranges. If you’re consistently below the range, your midwife may want to check you’re getting everything you and your baby need. If you’re consistently above it, the advice is to focus on a balanced diet and staying active, not to restrict food or diet — pregnancy is never the right time to try to lose weight without medical supervision.
Do I need to eat more because I’m pregnant?
Not as much as the “eating for two” myth suggests. The NHS advises that most people don’t need extra calories in the first two trimesters, and around 200 extra calories a day in the third trimester — roughly two slices of wholemeal toast with margarine. Eating substantially more than this isn’t necessary and may increase the risk of gaining more than the typical range.
Does this calculator give me a personal weight gain target?
No. It shows a general, population-level reference range based on published guidelines, for general information only. It is not a personalised target, a diagnosis, or medical advice. Your midwife or GP is best placed to advise on what’s right for your individual pregnancy.