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Pre-pregnancy BMI
Pregnancy Weight Gain Calculator
How much weight to gain during pregnancy depends mainly on your weight before pregnancy. This calculator finds your pre-pregnancy BMI category and shows the healthy total weight gain range for that category, based on Institute of Medicine (IOM) guidelines — plus a weekly-rate guide and, if you enter your current weight, how your own gain compares.
Please enter a valid height and pre-pregnancy weight (both greater than 0).
Recommended total weight gain
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Category
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Typical weekly rate
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Gained so far
How to Use the Pregnancy Weight Gain Calculator
- Enter your height and your weight from before pregnancy.
- Tick the twins box if relevant — the recommended range is higher for twin pregnancies.
- Optionally add your current weight, and your current week, to see how your own gain compares.
- Select Calculate to see your BMI category and recommended range.
Pregnancy Weight Gain Calculator — How It Works
BMI = weight (kg) ÷ height (m)² → IOM total-gain range by BMI category
Your pre-pregnancy BMI decides which recommended range applies: under 18.5 (underweight), 18.5–24.9 (normal weight), 25–29.9 (overweight), or 30 and above (obese). Each category has its own total weight gain range and its own typical weekly rate of gain for the second and third trimesters — women who start pregnancy underweight are advised to gain more, and women who start pregnancy in a higher BMI category are advised to gain less, per the Institute of Medicine's guidelines.
If you enter your current weight and current week, the tool compares your actual gain against an approximate typical pace: roughly the midpoint of the first-trimester total (about 1.25 kg by week 13), plus your category's weekly rate for each week after that. This is a rough guide, not a precise target — actual healthy pregnancies vary week to week.
Pregnancy Weight Gain Calculator Example
A woman who is 165 cm tall and weighed 60 kg before pregnancy has a pre-pregnancy BMI of 22.0 — normal weight. Her recommended total gain is 11.5–16 kg, at a typical rate of about 0.4 kg per week through the second and third trimesters. If she enters a current weight of 68 kg at week 20, the tool shows she's gained 8 kg so far, against a typical pace of roughly 4.05 kg by week 20 — above the typical pace for that week.
When to use this tool
Use this early in pregnancy to understand your target range, and again later to check your own gain against a general guideline — alongside, not instead of, your prenatal appointments.
Key Features & Benefits of This Pregnancy Weight Gain Calculator
- Based on IOM guidelines — the standard reference used by health authorities and clinicians.
- Twin-aware — shows the higher recommended range for twin pregnancies where it's established.
- Optional progress check — compare your actual gain against an approximate typical pace.
- Instant, free and private — runs entirely in your browser, no sign-up, nothing stored.
Good to know
This tool gives general, population-level guidance — it is not medical advice and doesn't replace your midwife's or doctor's assessment, which accounts for your individual health, any pregnancy complications, and your full history. If you have concerns about your weight gain in either direction, or about your health during pregnancy, speak with your prenatal care provider.
Pregnancy Weight Gain Calculator — FAQs
How is my pre-pregnancy BMI category determined?
From your pre-pregnancy height and weight, using the standard BMI formula and the usual adult BMI cut-offs: under 18.5 is underweight, 18.5 to 24.9 is normal weight, 25 to 29.9 is overweight, and 30 or above is obese.
Why is the recommended range higher for twins?
A twin pregnancy needs more total weight gain to support two babies, placentas and the extra tissue involved. Twin-specific ranges are only well established for normal weight, overweight and obese categories; for an underweight pre-pregnancy BMI with twins, this tool shows the singleton range because twin-specific guidance isn't well established.
What if I'm gaining faster or slower than this range?
These are population-level guidelines, and individual pregnancies vary for many reasons. Being outside the range isn't a diagnosis of anything by itself — discuss your own weight gain pattern with your midwife or doctor, who can see your full history.
Where do these numbers come from?
From the U.S. Institute of Medicine's 2009 pregnancy weight gain guidelines, the most widely used reference for this topic, cross-checked here against the Merck/MSD Manual's clinical reference tables.