Pregnancy Weight Gain Calculator
Track pregnancy weight gain against IOM guidelines for your pre-pregnancy BMI.
About Pregnancy Weight Gain Calculator
The Institute of Medicine (IOM) 2009 guidelines recommend different total weight gain ranges during pregnancy depending on pre-pregnancy BMI. The ranges account for the baby's weight, placenta, amniotic fluid, increased blood volume and breast tissue. Gaining within the recommended range is associated with better outcomes for both mother and baby.
Formula
Pre-pregnancy BMI
BMI = weight (kg) / height (m)²
Worked example
With the default values below, Pregnancy Weight Gain Calculator returns Weight gained so far of 7.0. Change any input above and every figure here is recalculated in your browser.
Inputs used
- Pre-pregnancy height (cm)accepts 100–220
- 165
- Pre-pregnancy weight (kg)accepts 30–250
- 65
- Current weight (kg)accepts 30–300
- 72
- Current gestational age (weeks)accepts 1–42
- 20
- Carrying twins?
- No
Results
- Weight gained so far
- 7.0 kg
- Pre-pregnancy BMI
- 23.9
- BMI category
- Normal weight
- IOM recommended min (total)
- 11.5 kg
- IOM recommended max (total)
- 16.0 kg
- Expected gain by now (min)
- 3.4 kg
- Expected gain by now (max)
- 5.6 kg
- Status vs. IOM guideline
- Above recommended range
- Remaining gain needed (min)
- 4.5 kg
- Remaining gain allowed (max)
- 9.0 kg
Step by step
- 1Pre-pregnancy BMI= 23.9
- 2BMI category= Normal weight
- 3IOM total gain range= 11.5 – 16 kg
- 4Weight gained so far= 7.0 kg
- 5Expected range at week 20= 3.4 – 5.6 kg
- 6Status= Above recommended range
Assumptions and limits
- The result is derived only from the 5 inputs listed above. Anything not among them is not part of the calculation.
- In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
- Figures are rounded for display to 1 decimal place, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.
- The weight gain ranges in this calculator are based on the 2009 IOM guidelines. They are population-level estimates for informational purposes only. Every pregnancy is different. Consult your healthcare provider for personalised guidance on gestational weight gain.
- This is an estimate for general information and not professional medical advice. See the full disclaimer for the limits that apply to this kind of calculator.
How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.
The weight gain ranges in this calculator are based on the 2009 IOM guidelines. They are population-level estimates for informational purposes only. Every pregnancy is different. Consult your healthcare provider for personalised guidance on gestational weight gain.
Frequently Asked Questions
What are the IOM 2009 recommended ranges?
Underweight (BMI < 18.5): 12.5–18 kg. Normal (18.5–24.9): 11.5–16 kg. Overweight (25–29.9): 7–11.5 kg. Obese (≥ 30): 5–9 kg. For twins with normal BMI the range is 17–25 kg.
Is the weekly rate of gain consistent throughout pregnancy?
No. In the first trimester the typical total gain is only 0.5–2 kg. Thereafter weight gain accelerates, with roughly 0.3–0.5 kg per week in the second and third trimesters. This calculator prorates the total range linearly, which is a simplification.
Should I be concerned if I'm outside the range?
Not necessarily — individual variation is normal, and weight gain can fluctuate week to week. Discuss any concerns with your midwife or obstetrician rather than attempting to restrict or force weight gain without medical supervision.