Gaining the right amount of weight lowers the risk of gestational diabetes, high blood pressure, a very large or small baby and caesarean birth. Most of the gain happens in the second and third trimesters.
How to use the Pregnancy Weight Gain Calculator
- Height
- Pre-pregnancy weight
- Current weight
- Weeks pregnant
- Expecting
Results update as you type, and every field accepts the units shown in its menu.
How it works
Enter your height, weight before pregnancy, current weight and how many weeks pregnant you are.
IOM 2009 recommendations
| Pre-pregnancy BMI | Total gain (one baby) | Weekly gain, 2nd–3rd trimester | Total gain (twins) |
|---|---|---|---|
| Below 18.5 | 12.5–18 kg (28–40 lb) | 0.44–0.58 kg | No guideline |
| 18.5–24.9 | 11.5–16 kg (25–35 lb) | 0.35–0.50 kg | 17–25 kg |
| 25–29.9 | 7–11.5 kg (15–25 lb) | 0.23–0.33 kg | 14–23 kg |
| 30 and above | 5–9 kg (11–20 lb) | 0.17–0.27 kg | 11–19 kg |
Tips
- Count from the first day of your last period, not the last day.
- An early ultrasound gives the most accurate due date.
- Track cycles for a few months to know your average length.
- Take a prenatal vitamin with folic acid when trying to conceive.
Common mistakes to avoid
- Using calendar methods as contraception.
- Expecting the baby on the exact due date – only about 4% arrive on it.
- Testing for pregnancy too early, before hCG can be detected.
Inputs explained
| Field | What to enter |
|---|---|
| Height | Units: cm, in, m, ft, mm |
| Pre-pregnancy weight | Units: kg, lb, st, g |
| Current weight | Units: kg, lb, st, g |
| Weeks pregnant | A number |
| Expecting | Choose one: One baby, Twins |
What each result means
- Pre-pregnancy BMI = [Pre-pregnancy weight]÷([Height]÷100)^2
- Your gain so far = [Current weight] – [Pre-pregnancy weight]
Health note: this calculator is for education and screening only and is not a diagnosis or treatment advice. Discuss your results with a qualified clinician.
Formula
Pre-pregnancy BMI = weight ÷ height²Total gain (singleton): underweight 12.5–18 kg, healthy 11.5–16 kg, overweight 7–11.5 kg, obese 5–9 kgFirst trimester 0.5–2 kg, then weekly: 0.44–0.58, 0.35–0.50, 0.23–0.33 or 0.17–0.27 kgWorked example
Inputs — Height: 165 cm; Pre-pregnancy weight: 60 kg; Current weight: 66 kg; Weeks pregnant: 20; Expecting: One baby.
Results — Pre-pregnancy BMI = 22; BMI category = Healthy weight; Recommended total gain – from = 11.5 kg; Recommended total gain – to = 16 kg; Recommended gain by now – from = 2.9 kg; Recommended gain by now – to = 5.5 kg; Your gain so far = 6 kg; Compared with the recommendation = Above the recommended range.
Key terms
- IOM
- Institute of Medicine (now the National Academy of Medicine).
Frequently asked questions
How much weight should I gain in pregnancy?
11.5–16 kg (25–35 lb) with a healthy pre-pregnancy BMI.
Should I eat for two?
No – you need about 340 extra kcal a day in the second trimester and 450 in the third.
Is it safe to lose weight in pregnancy?
Deliberate weight loss is not usually advised; talk to your midwife.
What formula does the Pregnancy Weight Gain Calculator use?
Pre-pregnancy BMI = weight ÷ height².