# Pregnancy Weight Gain Calculator

> See the recommended total pregnancy weight gain for your pre-pregnancy BMI under the IOM 2009 guidelines, and the typical range for your current week.

Category: Health & fitness · Applies to: Worldwide · Last updated: 2026-10-29
Interactive calculator: https://calculators.geekmidst.com/calculators/pregnancy-weight-gain-calculator

How much weight to gain in pregnancy depends on your BMI before pregnancy. The Institute of Medicine (IOM, 2009) guidelines give a total range and a weekly rate for the second and third trimesters.

Also called: Gestational weight gain calculator.

## Inputs
- Units (options: Metric (cm, kg), US (ft, in, lb); default metric)
- Height (unit cm; default 165)
- Weight before pregnancy (unit kg; default 60)
- Current weight (unit kg; default 66)
- Height (feet) (unit ft; default 5)
- Height (inches) (unit in; default 5; optional)
- Weight before pregnancy (unit lb; default 132)
- Current weight (unit lb; default 145)
- Week of pregnancy (unit weeks; default 24)
- Pregnancy (options: One baby, Twins; default single)

## Results
- Recommended total gain
- Pre-pregnancy BMI
- BMI category
- Gained so far (kg or lb)
- Typical gain by this week
- Compared with the typical range

## Formula

```
BMI = pre-pregnancy kg ÷ m²;  by week w ≤ 13: first-trimester gain × w ÷ 13;  after 13 weeks: first-trimester gain + weekly rate × (w − 13)
```

Where:
- first-trimester gain: 0.5–2 kg (1.1–4.4 lb)
- weekly rate: IOM range for your BMI group, e.g. 0.35–0.50 kg a week for normal weight

## Worked example
1. Pre-pregnancy BMI = 60 ÷ 1.65² = 22.0: normal weight, so the IOM total is 11.5–16 kg.
2. By week 24 (11 weeks after week 13): 0.5 + 0.35 × 11 = 4.4 kg to 2 + 0.50 × 11 = 7.5 kg.
3. Gained so far: 66 − 60 = 6 kg, which is within that range.

**Result:** With a pre-pregnancy BMI of 22.0 the recommended total gain is 11.5–16 kg; 6 kg at 24 weeks is within the typical range.

## What the result means

The total range is the IOM recommendation. The week-by-week figure is a guide built from the IOM’s assumed first-trimester gain and weekly rates, so small differences from it are not a concern. Your midwife or doctor will interpret your gain alongside your baby’s growth and your health.

## Assumptions and limits
- IOM (2009) totals: underweight 12.5–18 kg (28–40 lb), normal 11.5–16 kg (25–35 lb), overweight 7–11.5 kg (15–25 lb), obese 5–9 kg (11–20 lb).
- Second- and third-trimester weekly ranges: 0.44–0.58, 0.35–0.50, 0.23–0.33 and 0.17–0.27 kg (1.0–1.3, 0.8–1.0, 0.5–0.7, 0.4–0.6 lb).
- Provisional twin totals: normal 16.8–24.5 kg (37–54 lb), overweight 14.1–22.7 kg (31–50 lb), obese 11.5–19.1 kg (25–42 lb).
- No IOM twin guideline exists for a pre-pregnancy BMI under 18.5, and no week-by-week twin ranges are given.
- Not for pregnancies with three or more babies.
- Does not replace advice from your maternity care team.

## Questions

### Why is less gain recommended with a higher BMI?

The guidelines balance risks to mother and baby; with more stored energy before pregnancy, a smaller gain is associated with better outcomes.

### I am losing weight in the first trimester because of sickness. Is that a problem?

Small losses with nausea are common early on, but tell your midwife or doctor, especially if you cannot keep fluids down.

## Sources
- [IOM 2009 recommendations table, reproduced in Ann Epidemiol 2014 (PMC4029921)](https://pmc.ncbi.nlm.nih.gov/articles/PMC4029921/table/T1)
- [Merck Manual Professional: Guidelines for weight gain during pregnancy](https://www.merckmanuals.com/professional/multimedia/table/guidelines-for-weight-gain-during-pregnancy)

## Related calculators
- [Pregnancy Calculator](https://calculators.geekmidst.com/calculators/pregnancy-calculator)
- [Due Date Calculator](https://calculators.geekmidst.com/calculators/due-date-calculator)
- [BMI Calculator](https://calculators.geekmidst.com/calculators/bmi-calculator)
- [Healthy Weight Calculator](https://calculators.geekmidst.com/calculators/healthy-weight-calculator)

_This is a general screening estimate for adults, not medical advice or a diagnosis. Talk to a qualified health professional about your health._

Source: GM¹X CalcVerse — https://calculators.geekmidst.com/calculators/pregnancy-weight-gain-calculator