Pregnancy Weight Gain Calculator
See your personalized healthy weight-gain range for the whole pregnancy and for your current week, based on your pre-pregnancy BMI and the IOM / ACOG guidelines. Works for single and twin pregnancies, in kg or lb.
Enter your height and pre-pregnancy weight to see your personalized healthy weight-gain range.
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Your weight-gain trajectory
The shaded band is the healthy range across pregnancy. The marker shows where week 20 falls.
Gain by trimester
Where the weight actually goes
Only a portion of pregnancy weight is fat stores — most supports your baby and body. Typical breakdown near term:
Gentle guidance for you
These ranges are population-level guidelines, not a personal target or a diet plan. Healthy pregnancies vary, and some weeks the scale moves more or less than expected — the overall trend matters more than any single week. Your midwife or doctor tracks your progress and sets the right target for you, especially with a twin pregnancy, a health condition, or any history of disordered eating. Always follow their advice over this tool.
How the pregnancy weight gain calculator works
Healthy weight gain in pregnancy isn’t one number — it’s a range that depends on where you started. This calculator takes your height and pre-pregnancy weight to work out your pre-pregnancy BMI, then applies the widely used Institute of Medicine (IOM 2009) guidelines, as adopted by ACOG, to give you a recommended total gain for the whole pregnancy and a cumulative range for your current week. If you add today’s weight, it gently compares your progress to the expected range and tells you whether you’re below, within, or above it — without judgement.
Don’t know your current week yet? Work it out first with our Pregnancy Due Date Calculator or explore each stage with the Pregnancy Week by Week Calculator.
Quick answer
For a single baby, the IOM recommends a total gain of about 28–40 lb (12.5–18 kg) if you started underweight, 25–35 lb (11.5–16 kg) at a normal BMI, 15–25 lb (7–11.5 kg) if overweight, and 11–20 lb (5–9 kg) with obesity. Most of it happens after the first trimester, at roughly half a pound to a pound per week.
Recommended weight gain by pre-pregnancy BMI
These IOM 2009 ranges are the ones your provider uses. They’re based on your BMI before pregnancy and apply to a single baby.
| Pre-pregnancy category | BMI | Total gain (single) | Weekly rate (2nd & 3rd tri) |
|---|---|---|---|
| Underweight | Below 18.5 | 28–40 lb · 12.5–18 kg | ~1–1.3 lb (0.5–0.6 kg) |
| Normal weight | 18.5–24.9 | 25–35 lb · 11.5–16 kg | ~0.8–1 lb (0.35–0.45 kg) |
| Overweight | 25–29.9 | 15–25 lb · 7–11.5 kg | ~0.5–0.7 lb (0.23–0.33 kg) |
| Obese | 30 or higher | 11–20 lb · 5–9 kg | ~0.4–0.6 lb (0.17–0.27 kg) |
Twin pregnancy weight gain
Carrying twins means a higher recommended range to support two babies, two placentas, and extra fluid and blood volume. For a single reference: normal-BMI is about 37–54 lb (17–25 kg), overweight 31–50 lb (14–23 kg), and obese 25–42 lb (11–19 kg). The IOM doesn’t give a specific twin range for an underweight starting BMI because there isn’t enough data — if that’s you, your provider will set a personalized target. Switch the calculator to “Twins” to apply these ranges. Planning your dates too? Our IVF Due Date Calculator is handy if your pregnancy came from egg retrieval or embryo transfer.
How the weekly range is calculated
Weight gain isn’t linear. In the first trimester, total gain is usually just 1–4 lb (0.5–2 kg) across every BMI category — and some people lose a little from morning sickness, which is normal if nutrition resumes. From week 14 onward, the calculator adds your category’s weekly rate for each week that’s passed. So your “expected by this week” figure is the first-trimester base plus the steady second- and third-trimester gain up to your current week. It’s a range, not a fixed number, because real bodies vary.
A worked example
Say you’re 5 ft 5 in (165 cm) and weighed 130 lb (59 kg) before pregnancy. That’s a BMI of about 21.6 — normal weight — so your recommended total is 25–35 lb. At 20 weeks, the expected cumulative gain lands around 6–11 lb. If you’ve gained 8 lb, you’re comfortably within range. If you’ve gained 15, your provider might simply talk through your eating and activity — one high reading is rarely a concern on its own.
Related maternal health calculators
This tool is part of the Maternal Health Calculators hub. These companion tools cover the tracking and monitoring side of pregnancy — each answers a different question, so pick whichever fits where you are.
Frequently asked questions
It depends on your pre-pregnancy BMI. For a single baby the IOM recommends about 28–40 lb if underweight, 25–35 lb at a normal BMI, 15–25 lb if overweight, and 11–20 lb with obesity. This calculator gives your exact range and how much is typical by your current week.
Usually just 1–4 lb (0.5–2 kg) total, across all BMI categories. Some people don’t gain any, or lose a little because of morning sickness. That’s generally fine as long as you’re able to eat and drink normally again afterward.
Yes, a small loss or no gain in the first trimester is common and usually not a concern. If you’re struggling to keep food or fluids down, or losing weight steadily, contact your provider so they can help.
It uses your weight and height from before pregnancy: BMI equals weight in kilograms divided by height in metres squared. In pounds and inches, multiply weight by 703, then divide by height in inches squared. Your starting category sets your recommended gain.
A single week above range rarely matters — water retention and meal timing shift the scale daily. If the trend stays high over several weeks, your provider may talk through nutrition and gentle activity. Never restrict food or diet during pregnancy without medical guidance.
Slower gain can be fine, especially early on, but consistently low gain is worth raising with your provider, who checks that your baby is growing well. They can suggest nutrient-dense foods and rule out any issues.
Only part of it is fat stores. The rest is your baby, placenta, amniotic fluid, a larger uterus, extra blood and fluid, and breast tissue. The calculator shows a typical breakdown near term so you can see it’s mostly supporting your pregnancy.
Yes. Twin pregnancies need more: about 37–54 lb at a normal BMI, 31–50 lb if overweight, and 25–42 lb with obesity. There’s no specific IOM twin range for underweight, so your provider sets that individually. Switch the toggle to “Twins.”
It applies the same IOM/ACOG ranges clinicians use, so it’s a reliable reference. But it’s general population guidance, not a personal medical target. Your provider accounts for your full history and your baby’s growth, which a calculator can’t.
Pregnancy is not a time for weight-loss diets. The focus is balanced nutrition and staying active as your provider advises, not restriction. If you have concerns about weight or eating, please talk to your provider, who can support you safely.
Methodology
This calculator computes pre-pregnancy BMI from your height and pre-pregnancy weight (weight in kg ÷ height in m², or weight in lb × 703 ÷ height in in²) and assigns the WHO BMI category. It then applies the Institute of Medicine 2009 gestational weight-gain guidelines, as adopted by ACOG, to give a total recommended range for a singleton or twin pregnancy. Expected cumulative gain by week is modelled as the standard first-trimester gain of about 1–4 lb (0.5–2 kg) interpolated across weeks 1–13, plus the category-specific weekly rate applied from week 14 to your current week. Twin weekly progress is estimated proportionally from the total twin range because the IOM does not specify week-by-week twin targets. The composition breakdown reflects typical values near term for a normal-weight singleton pregnancy. All figures are population-level ranges for education, not personal medical targets or a diet plan, and are not a substitute for care from a qualified provider.
Reviewer
References & trusted sources
- ACOG — Weight Gain During Pregnancy (Committee Opinion 548)
- Institute of Medicine (2009) — Weight Gain During Pregnancy: Reexamining the Guidelines
- CDC — Weight Gain During Pregnancy
- NHS — Weight management in pregnancy
Last reviewed & updated: July 2026.
Weight can be a sensitive subject. If thinking about weight or eating in pregnancy feels distressing, you’re not alone — please reach out to your midwife, doctor, or a support line. In the US, the National Alliance for Eating Disorders helpline (1-866-662-1235) can help.