Pregnancy Weight Gain Calculator
IOM 2009 recommended weight-gain ranges by pre-pregnancy BMI.
Quick answer
- Formula: Pre-pregnancy BMI = weight ÷ height², then IOM 2009 ranges: <18.5 → 12.5–18 kg · 18.5–24.9 → 11.5–16 kg · 25–29.9 → 7–11.5 kg · ≥30 → 5–9 kg
- Worked example — Pre-pregnancy BMI: 23.9 (full example below).
Pregnancy Weight Gain Calculator
| Pre-pregnancy BMI | 23.9 |
| BMI category | Normal weight (BMI 18.5-24.9) |
| Recommended total gain (IOM 2009) | 11.5-16 kg (25-35 lb) |
| Suggested rate, 2nd & 3rd trimester | 0.35-0.50 kg per week |
At 65 kg and 165 cm, pre-pregnancy BMI is 23.9 — normal weight — so the IOM 2009 recommendation is a total gain of 11.5–16 kg (25–35 lb), at about 0.35–0.50 kg per week in the second and third trimesters.
The Institute of Medicine's 2009 guidelines (used by ACOG) set recommended pregnancy weight-gain ranges according to pre-pregnancy BMI: underweight (below 18.5) 12.5–18 kg, normal weight (18.5–24.9) 11.5–16 kg, overweight (25–29.9) 7–11.5 kg, and obese (30+) 5–9 kg for a single baby. This calculator works out your category from height and pre-pregnancy weight, then shows the total range and the suggested weekly rate for the second and third trimesters.
These are population guidelines for singleton pregnancies — twins, medical conditions and individual circumstances change the target, so confirm your personal range with your midwife or doctor. Educational information only, not medical advice.
The formula
Worked example
At 65 kg and 165 cm, pre-pregnancy BMI is 23.9 — normal weight — so the IOM 2009 recommendation is a total gain of 11.5–16 kg (25–35 lb), at about 0.35–0.50 kg per week in the second and third trimesters.
The example is pre-loaded in the result panel — press Calculate with your own numbers to replace it.
Frequently asked questions
How much is gained in the first trimester?
Typically only 0.5–2 kg in total. The weekly rates shown apply to the second and third trimesters, after the first-trimester allowance the IOM builds into its ranges.
What if I am carrying twins?
IOM provisional ranges for twins are higher: 16.8–24.5 kg for normal-weight, 14.1–22.7 kg for overweight and 11.3–19.1 kg for obese pre-pregnancy BMI. This calculator covers singleton pregnancies.
Where does the gained weight go?
Only part is body fat: a typical term gain includes the baby (~3.4 kg), placenta, amniotic fluid, increased blood volume, breast and uterine tissue and fluid — which is why gains well above fat storage alone are expected and healthy.
Category: Health & Fitness calculators
Sources & methodology
This calculator applies the formula shown on this page exactly as written, using the standard definitions for its inputs. Results are computed from the values you enter — no data is stored — and are rounded only for display.
Content last reviewed by CalcHub Editorial.
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