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Pregnancy Weight Gain Calculator
See how much weight gain is recommended over a pregnancy for your pre-pregnancy BMI, based on the 2009 Institute of Medicine guidelines. Enter your height, your weight before pregnancy and your current week to get the recommended total and an expected weight range for this week.
- Pre-pregnancy BMI
- 23.3
- BMI group
- Normal weight (BMI 18.5–24.9)
- Weight range this week — from
- 147.3 lb
- Weight range this week — to
- 152.3 lb
- Weight at 40 weeks — from
- 165 lb
- Weight at 40 weeks — to
- 175 lb
Saved setups
Save a set of inputs you reuse — your usual rate, your loan, your room sizes — and load it back in one tap.
Your recent calculations
Results you calculate here are kept on this device so you can come back to them.
Formula
How to use it
- Enter your height and your weight before you became pregnant.
- Enter the week of pregnancy you are in.
- Tick the box if you are expecting twins.
- Read the recommended total gain and the weight range for your current week and for 40 weeks.
Worked examples
5 ft 5 in and 140 lb before pregnancy, now at week 20
- Pre-pregnancy BMI
- 23.3
- BMI group
- Normal weight (BMI 18.5–24.9)
- Recommended total gain
- 25–35 lb (11.5–16 kg)
- Weight range this week — from
- 147.3 lb
- Weight range this week — to
- 152.3 lb
- Weight at 40 weeks — from
- 165 lb
- Weight at 40 weeks — to
- 175 lb
170 cm and 90 kg before pregnancy, now at week 30
- Pre-pregnancy BMI
- 31.1
- BMI group
- Obesity (BMI 30 or more)
- Recommended total gain
- 11–20 lb (5–9 kg)
- Weight range this week — from
- 205.7 lb
- Weight range this week — to
- 212.6 lb
- Weight at 40 weeks — from
- 209.4 lb
- Weight at 40 weeks — to
- 218.4 lb
The IOM 2009 ranges
For one baby the recommended total gain is 28–40 lb (12.5–18 kg) if you were underweight, 25–35 lb (11.5–16 kg) at a normal weight, 15–25 lb (7–11.5 kg) if overweight and 11–20 lb (5–9 kg) with obesity. The guidelines assume a gain of 1.1–4.4 lb (0.5–2 kg) in the first trimester, with most of the gain coming steadily in the second and third.
For twins, the provisional ranges are 37–54 lb (17–25 kg) at a normal weight, 31–50 lb (14–23 kg) if overweight and 25–42 lb (11–19 kg) with obesity. The IOM gave no twin guideline for underweight women, and the week-by-week range is shown for single pregnancies only.
Reading the weekly range
The week-by-week figures are a straight-line interpolation between the first-trimester allowance and the total, to give a sense of the track. Real gain is uneven — a few pounds one month and little the next is normal — so a single weigh-in outside the range means little on its own.
This is an estimate for general information, not medical advice. Talk to a doctor or other qualified clinician before making health decisions based on it.
Questions people ask
How much weight should I gain during pregnancy?
With a pre-pregnancy BMI in the normal range (18.5–24.9), the recommended total is 25–35 lb (11.5–16 kg). It is higher if you started underweight and lower if you started overweight.
How much weight should I have gained by 20 weeks?
On an even track for a normal pre-pregnancy BMI, roughly 7 to 12 lb. Someone who started at 140 lb would be at about 147 to 152 lb.
Which BMI do I use, before pregnancy or now?
Your BMI from before you became pregnant. The guideline groups are defined by pre-pregnancy weight, and BMI is not meaningful once you are pregnant.