Pregnancy Weight Gain Calculator
Calculate your recommended pregnancy weight gain based on pre-pregnancy BMI using IOM guidelines. Track if you're on target for a healthy pregnancy.
About this calculator
This calculator estimates recommended pregnancy weight gain and compares it against your actual progress. From Pre-Pregnancy Weight, Height (feet), and Height (inches), it computes Pre-Pregnancy BMI (weight in kilograms divided by height in meters squared) and sorts it into one of four IOM (Institute of Medicine) categories -- Underweight, Normal Weight, Overweight, or Obese -- each carrying its own Recommended Gain range taken directly from the IOM's 2009 pregnancy weight gain guidelines (28-40 lbs for Underweight, 25-35 lbs for Normal Weight, 15-25 lbs for Overweight, and 11-20 lbs for Obese). Current Weight Gain is simply Current Weight minus Pre-Pregnancy Weight, so raising Current Weight increases it and raising Pre-Pregnancy Weight lowers it by an equal amount per pound; because the two inputs sit close in magnitude but Current Weight is the larger of the two at typical defaults, a given percentage change in Current Weight moves the gain figure slightly more than the same percentage change in Pre-Pregnancy Weight.
Weight Gain Status compares that figure to an expected-gain curve built from the recommended range: roughly 10% of the total in the first trimester (weeks 1-13), then the remainder spread evenly across weeks 14-40. Recommended Weekly Gain divides whatever is left of the recommended range by the weeks remaining until week 40. This tool applies population-level IOM guidance -- it does not account for multiples (twins/triplets), pre-existing conditions, or a clinician's individualized recommendation, which should always take precedence.
Medical Disclaimer
This calculator is for informational and educational purposes only. It is not a substitute for professional medical advice, diagnosis, or treatment. Always consult a qualified healthcare provider before making decisions about your health. Never disregard professional medical advice or delay seeking it because of results from this tool.
Inputs
Results
Weight Gain Status
On track
Figures current as of 2009. Source: Institute of Medicine and National Research Council, Weight Gain During Pregnancy: Reexamining the Guidelines (2009), as reproduced by the CDC
How to Use This Calculator
- Enter Pre-Pregnancy Weight, Height (feet), and Height (inches).
- Set Current Week of Pregnancy and Current Weight.
- Review the Weight Gain Status result.
- Use Current Weight Gain (lbs) and Pre-Pregnancy BMI to inform your decision.
- Use the chart to visualize the results and explore different scenarios by adjusting inputs.
What each input means
- Pre-Pregnancy Weight
- Your weight before becoming pregnant.
- Height (feet)
- Height in feet.
- Height (inches)
- Additional inches beyond feet.
- Current Week of Pregnancy
- How many weeks pregnant are you?
- Current Weight
- Your current weight.
How this is calculated
Worked example, using the default values
- Identify Input Parameters4 parametersPre-Pregnancy Weight = 140, Height (feet) = 5, Height (inches) = 5, Current Week of Pregnancy = 20 = 5 input(s) provided
- Calculate Weight Gain StatusOn track = On track
- Calculate Current Weight GainCurrent Weight Gain10 = 10
- Calculate Pre-Pregnancy BMIPre-Pregnancy BMI23.3 = 23.3
Figures and sources
- IOM (Institute of Medicine) total pregnancy weight gain ranges by pre-pregnancy BMI category (2009) — Institute of Medicine and National Research Council, Weight Gain During Pregnancy: Reexamining the Guidelines (2009), as reproduced by the CDC
Engine last updated . Checked against 4 independently-derived tests — how we verify calculators. Built by Paul Gunder, a software engineer, not a licensed financial, medical, or legal professional.
Frequently Asked Questions
Why does my Current Weight move the results more than my Pre-Pregnancy Weight?
Current Weight Gain is calculated as Current Weight minus Pre-Pregnancy Weight, so both inputs shift the result by exactly one pound per pound changed -- but because Current Weight is typically the larger of the two numbers, an equal percentage change in Current Weight translates into a slightly bigger raw change than the same percentage change in Pre-Pregnancy Weight.
How is my BMI category determined?
Pre-Pregnancy BMI is calculated from your Pre-Pregnancy Weight and height using the standard formula (weight in kilograms divided by height in meters squared), then sorted into four IOM categories: Underweight (BMI under 18.5), Normal Weight (18.5-24.9), Overweight (25-29.9), or Obese (30 and above). Each category carries its own recommended total weight gain range published in the Institute of Medicine's 2009 pregnancy weight gain guidelines: 28-40 lbs for Underweight, 25-35 lbs for Normal Weight, 15-25 lbs for Overweight, and 11-20 lbs for Obese.
Why does the expected gain curve change after the first trimester?
The calculator assumes only about 10% of your total recommended gain happens during the first trimester (weeks 1-13), reflecting the modest weight change typical of early pregnancy, then spreads the remaining 90% evenly across weeks 14 through 40. This produces a much steeper expected weekly gain rate in the second and third trimesters than in the first.
Does this account for twins or a high-risk pregnancy?
No. The recommended gain ranges come from IOM guidelines for a single, otherwise typical pregnancy. Carrying multiples, having a pre-existing condition, or receiving individualized guidance from your prenatal care provider can all change your appropriate target, and provider guidance should always override this general estimate.
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