Pregnancy Weight Calculator
Your Starting BMI Sets the Target Range
Weight gain guidance in pregnancy isn't a single number — it's a range, and which range applies depends entirely on the body mass index you carried into pregnancy. A person who started underweight is guided toward gaining more than someone who started in a higher BMI category. This calculator takes your pre-pregnancy height and weight, works out that starting BMI, and returns the total-gain range that applies to it.
The Formula
Total recommended gain is then read from Institute of Medicine (IOM) guidelines for a singleton pregnancy, based on which BMI band the result falls into.
IOM Recommended Total Gain by Pre-pregnancy BMI
| Pre-pregnancy BMI | Category | Recommended total gain |
|---|---|---|
| Below 18.5 | Underweight | 28–40 lb (12.7–18.1 kg) |
| 18.5 – 24.9 | Normal weight | 25–35 lb (11.3–15.9 kg) |
| 25.0 – 29.9 | Overweight | 15–25 lb (6.8–11.3 kg) |
| 30.0 and above | Obese | 11–20 lb (5.0–9.1 kg) |
These are IOM ranges for a single baby; twin and multiple pregnancies use separate, higher targets not covered by this calculator.
Why a Range, Not a Number
- Early planning — knowing your target range at the first prenatal visit gives you a benchmark to check progress against at each later appointment.
- Flagging outliers early — gaining well outside your range, in either direction, is something to raise with a provider sooner rather than at a late scan.
- Context for competing advice — generic "25 to 35 pounds" advice circulating online is specifically the normal-BMI range; it doesn't apply uniformly to everyone.
How to Use This Calculator
- Choose Metric (cm / kg) or Imperial (in / lb) units.
- Enter your pre-pregnancy Height.
- Enter your pre-pregnancy Weight.
- Select Calculate for your pre-pregnancy BMI, its category, and the recommended total weight gain range.
Related Calculations
To check your gain-to-date against a week-by-week pacing of that same range, use the Pregnancy Weight Gain Calculator. For a due date to plan around, see the Due Date Calculator.