Quick answer: At 60 kg and 165 cm before pregnancy (BMI 22.0, normal weight), the IOM recommends a total gain of 11.5–16 kg with one baby, about 0.35–0.5 kg a week after the first trimester; by week 20 that is about 3–5.5 kg.
How it's calculated
The recommendation depends on your body mass index before pregnancy, BMI = weight (kg) ÷ height (m)². The US Institute of Medicine (IOM, now the National Academy of Medicine) published the ranges in 2009, and ACOG and most Gulf health services use them.
With one baby, the IOM assumes a gain of 0.5 to 2 kg in the first trimester, followed by a steady weekly gain in the second and third trimesters. The calculator spreads the first-trimester amount evenly over weeks 0–13 and then adds the IOM weekly rate (0.35–0.50 kg a week for a normal BMI), to give a range for the week you enter. Some calculators instead spread the total range evenly from week 13 to week 40, which gives slightly higher figures in mid-pregnancy.
For twins the IOM set provisional total ranges for normal-weight, overweight and obese women, and none for underweight women. The ranges describe healthy averages; your own target can differ with your health, age and how the pregnancy goes, and your doctor or midwife will tell you if it does.
Worked examples
- 60 kg, 165 cm, week 20, one baby: BMI 22.0 → total 11.5–16 kg; by week 20: 0.5 + 7 × 0.35 to 2 + 7 × 0.5 = 2.95–5.5 kg
- 80 kg, 165 cm, twins: BMI 29.4 (overweight) → 14–23 kg
- 132 lb, 5 ft 5 in, one baby: BMI 22.0 → 25–35 lb, 0.8–1 lb a week
IOM 2009 recommendations
| BMI before pregnancy | One baby | Per week (2nd–3rd tri.) | Twins |
|---|---|---|---|
| Under 18.5 | 12.5–18 kg (28–40 lb) | 0.44–0.58 kg (1–1.3 lb) | No guideline |
| 18.5–24.9 | 11.5–16 kg (25–35 lb) | 0.35–0.50 kg (0.8–1 lb) | 17–25 kg (37–54 lb) |
| 25–29.9 | 7–11.5 kg (15–25 lb) | 0.23–0.33 kg (0.5–0.7 lb) | 14–23 kg (31–50 lb) |
| 30 and above | 5–9 kg (11–20 lb) | 0.17–0.27 kg (0.4–0.6 lb) | 11–19 kg (25–42 lb) |
Frequently asked questions
Do I need to eat for two?
No. Energy needs rise only modestly: little or nothing extra in the first trimester, then roughly 340 extra calories a day in the second and 450 in the third, according to ACOG.
What if I gain more or less than the range?
Gaining well above or below the range is linked to more pregnancy and birth complications, but a single reading means little. Your doctor looks at the trend over several visits.
Which weight should I use as 'before pregnancy'?
Your weight just before you became pregnant, or at your first antenatal visit in early pregnancy if you don't know it.
How much should I gain with twins?
The IOM ranges for twins are higher: about 17 to 25 kg for a normal pre-pregnancy BMI, 14 to 23 kg for overweight and 11 to 19 kg for obesity.
How much should I gain in the first trimester?
Usually only about 0.5 to 2 kg in total. Most of the gain comes after week 13. Nausea can mean little or no gain early on, so mention it to your doctor if you're losing weight.
Where does the extra weight go?
To the baby, placenta, amniotic fluid, larger uterus and breasts, extra blood and fluid, and fat stores for breastfeeding. The baby is only about a quarter of the total.