Pregnancy Weight Gain Calculator

What is a pregnancy weight gain calculator?

A pregnancy weight gain calculator shows the recommended total weight-gain range from the Institute of Medicine (IOM) for your pre-pregnancy BMI, and estimates where you should be at your current week. It’s a guideline for a healthy pregnancy pace, not a judgement.

How this calculator works

• Enter your pre-pregnancy BMI and current week of pregnancy.
• It maps your BMI to the IOM total-gain band — underweight, normal, overweight, or obese.
• A trimester breakdown estimates the range you should be at this week.
• It shows the recommended weekly pace for the second and third trimesters.

How to use the result

1. Focus on the weekly pace in the second half — that’s the actionable number month to month.
2. Don’t aim for a specific number; aim to stay in the band and discuss with your provider.
3. Gain is rarely linear — early nausea can stall it, and the last trimester accelerates it.
4. Your doctor may set a different target for twins, pre-existing conditions, or your starting health.

How much weight should you gain during pregnancy?

IOM guidance: about 12.5–18 lb for underweight, 11.5–16 for normal weight, 7–11.5 for overweight, and 5–9 for obese. Gaining within the band lowers risks for both mother and baby, but the range is wide — the trend over the pregnancy matters more than any single week.

Common mistakes

• Gaining to the range in the first trimester. The first trimester should add only a few pounds; most gain comes after week 13.
• Using your current BMI. Pre-pregnancy BMI determines the band — your current BMI changes as the pregnancy progresses.
• Treating the range as a target to hit exactly. It’s a healthy band, and every pregnancy is different.

Weight gain is tracked against the pregnancy timeline — the due date calculator sets that timeline. Around the milestones, the BMI calculator explains the BMI scale, and the TDEE calculator shows how calorie needs rise in later trimesters.