Example 1 — Normal weight, week 20
- BMI: 22
- Week: 20
- Singleton, moderate activity
~4.3 kg (3.3 kg–5.6 kg)
A typical course for normal BMI at mid-pregnancy — total recommended by delivery is 11.5 kg–16 kg.
Pregnancy weight gain calculator
Enter your pre-pregnancy BMI and current week — you'll see the weight-gain range that usually fits that starting point.
We estimate cumulative gain from your pre-pregnancy BMI category (IOM/NASEM guidelines) and current week. Enter BMI, or pre-pregnancy weight and height. The result is a rough range — every pregnancy sets its own pace. Questions about your case? Your doctor or midwife.
Result
Enter BMI (or weight and height) and week of pregnancy.
How results are calculated
BMI category (pre-pregnancy): underweight < 18.5; normal weight 18.5–24.9; overweight 25–29.9; obesity ≥ 30 — each has a different recommended total gain by delivery (IOM).
Cumulative gain: small 1st-trimester gain (~0.5–2 kg) through week 13, then a linear rate in kg toward the IOM band.
Cumulative gain: small 1st-trimester gain (~1–4.5 lb) through week 13, then a linear rate in lb. Enter pre-pregnancy weight/height in header units (lb/in).
How to use the calculator
- Enter your pre-pregnancy BMI, or your weight and height — the calculator computes BMI for you.
- Enter the current week of pregnancy (1–42).
- Check multiple pregnancy if applicable, and optionally an activity level.
- Click Calculate or watch the live result as you type.
- Check the range indicator below the form — it shows where the estimated gain falls.
Usage examples
Example 2 — Obesity, week 30
- BMI: 32
- Week: 30
- Singleton, moderate activity
~4.8 kg (3.3 kg–6.4 kg)
At higher BMI, guidelines recommend a smaller total gain (5 kg–9 kg by delivery) — that range is normal under the guidelines.
Example 3 — Twins, normal weight, week 24
- BMI: 19 (normal weight)
- Week: 24
- Multiple pregnancy (twins)
~9.4 kg (7.8 kg–11.2 kg)
Multiple pregnancy raises recommended gain — the calculator applies a simplified ×~1.6 adjustment.
FAQ
Where do the weight-gain ranges come from?
From Institute of Medicine (IOM/NASEM) guidelines based on pre-pregnancy BMI: underweight, normal, overweight, and obesity each have different total gain targets by term.
Why pre-pregnancy BMI, not today's?
Guidelines start from weight before pregnancy. That sets the range, no matter how much you've already gained.
What if I'm gaining more or less than this?
Week-to-week wiggles are normal. If the gap is large or sticks around, talk with your doctor — they know your full picture.
Why is the first trimester counted differently?
In the first 13 weeks, typical total gain is small (about 0.5–2 kg / 1–4.5 lb) regardless of BMI category. Most gain lands in the 2nd and 3rd trimesters.
How does a multiple pregnancy change things?
Twins and higher-order pregnancies usually need more gain. We apply a simplified bump — get precise advice from the doctor managing a multiple pregnancy.
Does activity affect the result?
The activity field lightly adjusts 2nd–3rd trimester pace. It's a rough tweak, not a workout plan — clear activity in pregnancy with your doctor.
Does this mean I'm gaining “too much” or “too little”?
No. We show a typical range, not a grade. Food and activity choices are best made with your doctor or midwife.
What else is worth opening nearby?
BMI for your pre-pregnancy category, the due-date tool for visit planning, or ovulation if you're trying to conceive.