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Learn more →Pregnancy Weight Gain Calculator — by pre-pregnancy BMI
Enter your pre-pregnancy weight, height, current week, and (optionally) your current weight. Using the IOM/CDC guidelines and your pre-pregnancy BMI, the calculator shows the recommended total weight gain, how much you'd expect to have gained by now, and whether you're on track.
Enter your pre-pregnancy weight, height, and current week.
How it works
How recommended weight gain is set
The most widely used guidelines come from the Institute of Medicine (now the National Academies, NASEM, 2009). They tie the recommended total gain to your weight before pregnancy, measured as body mass index (BMI). A person who started underweight is advised to gain more than someone who started with obesity, because the goal is healthy fetal growth without excess maternal gain.
Most of the gain happens in the second and third trimesters. In the first trimester, only about 0.5–2 kg (1–4.5 lb) is expected; after that, a fairly steady weekly rate is recommended, which is what this calculator uses to estimate how much you'd expect to have gained by a given week.
The BMI categories
For a single baby, the IOM total-gain ranges are: underweight (BMI under 18.5) 12.5–18 kg; normal weight (18.5–24.9) 11.5–16 kg; overweight (25–29.9) 7–11.5 kg; and obese (30+) 5–9 kg. In pounds these are roughly 28–40, 25–35, 15–25, and 11–20 lb.
Twin pregnancies need more: normal weight 16.8–24.5 kg (37–54 lb), overweight 14.1–22.7 kg (31–50 lb), and obese 11.3–19.1 kg (25–42 lb). The IOM did not set a firm range for underweight twin pregnancies, so treat that case as provisional and follow your provider's plan.
Gaining too little or too much
Gaining far below the range is linked to low birth weight and preterm birth; gaining far above it raises the chance of a large baby, a harder delivery, gestational diabetes, and weight that's harder to lose afterwards. Neither extreme is something to panic over from a single week's reading — the trend over time matters more.
These ranges are population guidelines, not personal targets. Your own clinician may recommend something different based on your health, how the pregnancy is progressing, and measurements at your visits. Always use their advice over a calculator.
Frequently asked questions
›How much weight should I gain in pregnancy?
It depends on your pre-pregnancy BMI. For a single baby the IOM ranges are 12.5–18 kg if underweight, 11.5–16 kg if normal weight, 7–11.5 kg if overweight, and 5–9 kg if obese.
›Why is the recommendation based on BMI?
Your starting weight affects how much extra is healthy for the baby's growth. Someone who began underweight benefits from gaining more; someone who began with obesity needs less.
›How much should I gain per week?
After the first trimester, roughly 0.35–0.5 kg per week at normal weight, more if underweight and less if overweight or obese. The first trimester adds only about 0.5–2 kg total.
›What if I'm carrying twins?
Twin pregnancies need more: about 16.8–24.5 kg at normal weight. There's no firm IOM range for underweight twins, so follow your provider's guidance.
›I've gained more than the range — is that bad?
One reading isn't a verdict; the trend matters. Consistently gaining above the range raises some risks, so mention it at your next visit rather than dieting on your own.
›I've gained very little — should I worry?
Early pregnancy nausea can slow gain, and many people catch up. If you're well below the range over several weeks, your provider can check that growth is on track.
›Does this replace my doctor's advice?
No. It applies population guidelines; your clinician may set a different target based on your health and how the pregnancy is going. Their advice comes first.
›Is my data saved?
No. Everything is calculated in your browser and nothing is sent to a server.
Sources & methodology
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DisclosureRelated tools
This tool is for general information only and is not medical advice, diagnosis, or treatment. Consult a qualified healthcare professional about your health.
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