Pregnancy weight gain calculator

Examples with different starting weights

All examples are for a singleton pregnancy. The inputs are pre-pregnancy weight and height, from which the calculator finds BMI and picks the matching IOM range.

• 50 kg and 170 cm (BMI 17.3, underweight), week 10: recommended gain so far 0.4-1.5 kg, 12.5-18 kg over the whole pregnancy.
• 60 kg and 165 cm (BMI 22.0, normal), week 20: recommended 2.9-5.5 kg, 11.5-16 kg over the whole pregnancy.
• 80 kg and 165 cm (BMI 29.4, overweight), week 30: recommended 4.4-7.6 kg, 7-11.5 kg over the whole pregnancy.
• 95 kg and 168 cm (BMI 33.7, obese), week 24: recommended 2.4-5 kg, 5-9 kg over the whole pregnancy.

How the weekly range is built

For the first 13 weeks the calculator spreads 0.5-2 kg evenly, so the range at week 13 is 0.5-2 kg. From week 14 it adds the weekly rate for your BMI category: 0.35-0.5 kg at normal weight, 0.44-0.58 kg if underweight, 0.23-0.33 kg if overweight and 0.17-0.27 kg if obese. At normal weight the range at week 14 is therefore 0.9-2.5 kg.

The upper limit never exceeds the total for the pregnancy. The lower limit at week 40, however, ends slightly below the total range: at normal weight the calculator shows 10-15.5 kg by week 40, while the overall recommendation is 11.5-16 kg. This is because the weekly rate is averaged, so a difference of a kilogram or so should not be read as a problem.

Expecting twins

For twins the IOM total ranges are provisional and no separate weekly rate for the second and third trimesters exists. The calculator spreads the total range evenly over weeks 14-40. For example, at 68 kg and 168 cm (BMI 24.1) the recommended gain by week 25 is 7.7-12 kg, and 16.8-24.5 kg over the whole pregnancy.

There is no twin guideline for underweight women. In that case the calculator shows the normal-weight range with a warning, but treat it only as a temporary guide: underweight combined with a multiple pregnancy is a situation where your doctor should set the appropriate gain.

Example: tracking weight through pregnancy

Take a woman who weighed 60 kg before pregnancy and is 165 cm tall. The calculator stays the same; only the week changes. Here is her actual gain next to the recommended range:

The picture is good, but between weeks 20 and 30 she gained 6 kg, or 0.6 kg a week, slightly faster than the normal-weight rate of 0.35-0.5 kg. That is not an alarm but a topic for the next visit, where the midwife looks at blood pressure, swelling and the baby's growth alongside weight. A single reading says little; what matters is whether the trend continues.

• Week 12, weight 61 kg: gain 1 kg, recommended 0.5-1.8 kg.
• Week 20, weight 64 kg: gain 4 kg, recommended 2.9-5.5 kg.
• Week 30, weight 70 kg: gain 10 kg, recommended 6.5-10.5 kg, so at the top of the range.
• By week 36 the recommendation is 8.5-13.5 kg, leaving room for about 3.5 kg more over the next six weeks.

Common mistakes that change the result

The most important thing is to enter your weight before pregnancy, not your current weight. Near a boundary this can switch the whole category. A woman who is 165 cm tall and weighed 67 kg before pregnancy has a BMI of 24.6 and a week-20 recommendation of 2.9-5.5 kg. If she enters her current weight of 71 kg at week 20, the BMI becomes 26.1, the category flips to overweight and the recommendation wrongly drops to 2.1-4.3 kg.

• Weighing at different times and in different clothes: to compare, weigh yourself at the same time of day, ideally in the morning after using the toilet.
• Comparing single weeks: fluid retention can shift weight by a kilogram within days, so look at the trend over several weeks.
• Slight weight loss during first-trimester nausea is common. Being below the lower limit at that stage is not automatically a problem, but let your midwife know.

When to report a weight change straight away

The calculator shows a statistical range, not whether your pregnancy is going well. Contact your midwife, doctor or emergency care immediately if your weight jumps within a few days together with swelling of the face or hands, a severe headache, vision problems or pain in the upper abdomen. These can be signs of pre-eclampsia, which needs prompt assessment.

Seek help just as quickly if nausea and vomiting stop you from eating and drinking and you are losing weight. If your gain is slower or faster than recommended without other symptoms, discuss it at your next visit. Cutting back on food on your own or eating more to "catch up" is not the answer in either case.