Pregnancy weight gain calculator

Type pre-pregnancy BMI or mass and height, plus the week. BMI 22 at week 20 is about 4.3 kg. BMI 32 at week 30 is about 4.8 kg. Every pregnancy sets its own pace.

IOM/NASEM ranges from pre-pregnancy BMI. Not a grade. Mass category lives on BMI. Ovulation lives on the ovulation calculator.

Input data

You can enter BMI manually, or leave it blank and provide pre-pregnancy weight and height instead - then BMI = weight / height².

Abbreviations

  • BMI (body mass index) - weight (kg) ÷ height² (m).
  • IOM/NASEM - Institute of Medicine / National Academies, source of pregnancy weight gain ranges.

A rough guide - it doesn't replace talking with a doctor or midwife.

Result

Enter BMI (or weight and height) and week of pregnancy.

How results are calculated

Pre-pregnancy BMI sets the IOM band by delivery: underweight under 18.5; normal 18.5-24.9; overweight 25-29.9; obesity from 30. A normal BMI aims at 11.5-16 kg total. Obesity aims at 5-9 kg.

These are IOM/NASEM guidelines, not a clinic order. The tables start from mass before pregnancy, not from today's weight.

Cumulative gain: through week 13 typical gain is small, about 0.5-2 kg (about 1-4.5 lb with a US header), whatever the category. From week 14 the calculator applies a linear rate in kg or lb toward the category band. Enter pre-pregnancy mass and height in the header units.

BMI 22 at week 20, singleton: about 4.3 kg, band 3.3-5.6. BMI 32 at week 30: about 4.8 kg (3.3-6.4), because the total target is lower. Twins at BMI 19 in week 24: about 9.4 kg (7.8-11.2). The correction here is simplified, about ×1.6.

Type pre-pregnancy BMI, or mass and height (the calculator computes BMI), week 1-42, optionally twins and activity, then Calculate. BMI may stay blank when you give mass and height. 62 kg and 165 cm give a BMI of about 22.8. Week alone, without one of those paths, is not enough.

Activity slightly adjusts the rate in the 2nd and 3rd trimester. A sketch, not a training plan. Week-to-week swings are normal; a large gap belongs with your prenatal clinician. Ovulation lives on the LMP calendar. Adult BMI bands do not judge pregnancy gain.

How to use

  1. Type pre-pregnancy BMI, for example 22, or mass and height, for example 62 kg and 165 cm.
  2. Type the pregnancy week, for example 20. The range is 1-42.
  3. Check multiple pregnancy if it applies. Activity may stay blank: then the rate stays neutral.
  4. Click Calculate. BMI 22 at week 20 gives about 4.3 kg (3.3-5.6). By delivery 11.5-16 kg.
  5. BMI 32 at week 30 gives about 4.8 kg, because the total target is lower. Ovulation lives on its own card.

Pre-pregnancy BMI and IOM ranges

Cumulative gain follows pre-pregnancy BMI and the week. BMI 22 at week 20 is about 4.3 kg; BMI 32 at week 30 is about 4.8 kg.

BMI
Body mass index from before pregnancy, not from today. 22 at week 20 is about 4.3 kg (3.3-5.6). You can type BMI or mass and height, such as 62 kg and 165 cm.
IOM
Institute of Medicine, the source of the delivery ranges in this calculator. A normal BMI aims at 11.5-16 kg total; obesity aims at 5-9 kg.
NASEM
National Academies, the same guideline line as IOM. The calculator maps underweight / normal / overweight / obesity from those tables.

Usage examples

Example 1

  • BMI: 22
  • Week: 20
  • Singleton, moderate activity

~4.3 kg (3.3 kg - 5.6 kg)

A typical course for normal BMI at mid-pregnancy - total recommended by delivery is 11.5 kg - 16 kg.

Example 2

  • BMI: 32
  • Week: 30
  • Singleton, moderate activity

~4.8 kg (3.3 kg - 6.4 kg)

At higher BMI, guidelines recommend a smaller total gain (5 kg - 9 kg by delivery) - that range is normal under the guidelines.

Example 3

  • BMI: 19 (normal weight)
  • Week: 24
  • Multiple pregnancy (twins)

~9.4 kg (7.8 kg - 11.2 kg)

Multiple pregnancy raises recommended gain - the calculator applies a simplified ×~1.6 adjustment.

Related calculators

BMI (body mass index)

BMI calculator: weight and height.

Use calculator →

Due date calculator

We compute EDD with Naegele's rule: first day of the last period (LMP) plus 280 days, adjusted if the cycle is not 28 days.

Use calculator →

Ovulation and fertile window

Ovulation calculator: the first day of your last period and cycle length.

Use calculator →

All health calculators

FAQ

How much gain at BMI 22 in week 20?

About 4.3 kg, band 3.3-5.6. By delivery a normal BMI aims at 11.5-16 kg. The midpoint of an IOM range, not an order.

Where do these ranges come from?

IOM/NASEM guidelines from pre-pregnancy BMI. Underweight, normal, overweight, and obesity have different totals by delivery.

Why pre-pregnancy BMI, not today's?

The guidelines start from mass before pregnancy. That number sets the band, no matter how much you have already gained.

How much at BMI 32 in week 30?

About 4.8 kg (3.3-6.4). Obesity aims at 5-9 kg total, so week 30 shows less than BMI 22 at mid-pregnancy.

Why is the first trimester different?

Through week 13 typical gain is small, about 0.5-2 kg, whatever the category. Most gain lands in the 2nd and 3rd trimester.

How do twins change the result?

Gain is higher. BMI 19 in week 24: about 9.4 kg. The correction here is simplified, about ×1.6.

Does activity change the number?

It slightly adjusts the rate in the 2nd and 3rd trimester. A sketch, not a training plan. Activity in pregnancy you set with your doctor.

Does this mean I am gaining too much or too little?

No. We show a typical range, not a grade. Week-to-week swings are normal. A large gap belongs with your prenatal clinician.

Can I leave BMI blank?

Yes, if you type pre-pregnancy mass and height. 62 kg and 165 cm give about 22.8. Week alone, without one of those paths, is not enough.

Where are ovulation and regular BMI?

Ovulation lives on the LMP calendar. Adult BMI bands do not judge pregnancy gain; here the inputs are the pre-pregnancy category and the week.

Knowledge sources

The gain ranges come from IOM / NASEM guidelines. This is not a clinic chart.

Page updated in 2026.