Calculated using standard mathematical and industry formulas.
Free online Pregnancy Weight Gain Calculator calculator and unit conversion tool for everyday, engineering, and home projects.
How to use this calculator?
Select your unit system (metric or imperial).
Enter your pre-pregnancy height and pre-pregnancy weight.
Enter your current pregnancy week (1 to 40).
Select single baby or twin pregnancy to view recommended total gain and current target weight range.
Formula & calculation method
IOM 2009 Pregnancy Weight Gain Guidelines
Total Target Gain = Range(Pre-Pregnancy BMI Category, Twin Status)
Normal BMI (18.5–24.9): 11.5–16 kg (25–35 lbs). Underweight: 12.5–18 kg. Overweight: 7–11.5 kg. Obese: 5–9 kg.
Step-by-step calculation example
Pre-pregnancy weight 65 kg at 170 cm (BMI 22.5, Normal): Total target 11.5–16.0 kg. At week 20: recommended gain ~3.0–5.5 kg.
Key insights to remember
Recommended weight gain depends heavily on pre-pregnancy Body Mass Index (BMI).
During the first trimester (weeks 1–13), total weight gain is minimal (typically 0.5–2 kg / 1–4 lbs).
In the second and third trimesters, healthy weight gain averages 0.35–0.5 kg (0.8–1 lb) per week for normal BMI.
Weight gain consists of the baby, placenta, amniotic fluid, increased blood volume, uterine tissue, and body fat stores.
How to interpret your results?
Recommended Total Weight Gain
The healthy overall weight gain range over the entire 40-week pregnancy based on Institute of Medicine guidelines.
Target Weight at Current Week
The expected total weight (pre-pregnancy weight plus healthy gain to date) for your current week.
Frequently asked questions
How do I use the Pregnancy Weight Gain Calculator calculator?
Enter your numerical input and select desired units to get instant accurate results.
How accurate are the conversions?
Conversions use official ISO conversion factors for maximum precision.
Does it convert metric and imperial units?
Yes, seamless conversions between metric (meters, kg) and imperial (feet, lbs) are supported.
Is my data stored?
No, all calculations execute 100% locally in your browser with zero data logging.
Can I use this for DIY or engineering projects?
Yes, it provides reliable estimates for construction, crafting, science, and everyday math.
What if I enter invalid inputs?
The calculator will display a friendly error prompt if non-numeric values are entered.
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