Pregnancy Weight Gain Calculator

Pregnancy weight gain range by BMI and week

This Pregnancy Weight Gain Calculator estimates a practical, week-by-week weight gain range for a singleton pregnancy using your pre-pregnancy Body Mass Index (BMI). The goal is simple: help you understand what “on track” usually looks like at your current pregnancy week, and what a reasonable total weight gain range might be by the end of pregnancy.

Most people searching for a pregnancy weight gain calculator are not trying to build a perfect medical model. They want a fast reality check: “Based on my starting point, how much weight gain is typically recommended, and am I roughly in range right now?” This calculator is built for that single decision. It does not attempt to manage medical conditions, pregnancy complications, or special cases that need clinician guidance.

To use it, enter your pre-pregnancy weight and height so the calculator can estimate your BMI category. Then enter your current pregnancy week (gestational age). The calculator returns: your estimated BMI, your BMI category, a recommended total weight gain range for a singleton pregnancy, and an estimated “target gain so far” range for your current week. If you also enter your current weight, it compares your gain to the range and labels you as below range, within range, or above range. It also shows how much gain remains to reach the low and high ends of the total range.

Assumptions and how to use this calculator

• This tool is for singleton pregnancies. It does not cover twins or higher multiples.
• Pre-pregnancy BMI is estimated from the weight and height you enter. If your starting weight is uncertain, use your best estimate and treat results as a range, not a verdict.
• First-trimester gain is modeled as a small range that applies up to week 13. After week 13, gain is modeled using a typical weekly rate range for your BMI category.
• Week-by-week targets are capped so they do not exceed the recommended total range at term. This prevents unrealistic “targets” late in pregnancy for some BMI categories.
• This calculator does not diagnose health issues. Swelling, fluid shifts, morning sickness, and medical conditions can change weight rapidly. Use this as a planning guide and discuss concerns with a clinician.

Common questions

Why does my recommended weight gain depend on BMI?

Pre-pregnancy BMI is a rough proxy for how much stored energy your body already has. Higher starting BMI often corresponds to a lower recommended total gain, while lower starting BMI often corresponds to a higher recommended gain. The intent is to support healthy fetal growth while reducing avoidable risks from excessive gain.

What if I do not know my exact pre-pregnancy weight?

Use your best estimate from before pregnancy or early first trimester. If you only have a later weight, this calculator cannot accurately back-calculate a starting point. Small errors in starting weight can move BMI across category boundaries, which can change the recommended ranges. Treat the output as an approximate guide and focus on trend and consistency over time.

What does “on track” mean in this calculator?

“On track” means your total gain so far falls within a typical cumulative gain range for your BMI category at your current pregnancy week. It is not a guarantee of health, and it is not a statement that you must stay inside the range every week. Real weight gain is uneven. This is a reasonable target band, not a strict rule.

Why can weight gain be slow in the first trimester?

Many people gain little weight in the first trimester due to nausea, appetite changes, or increased energy use. Some people lose weight early on. This calculator models the first trimester as a small range and then uses a steadier weekly rate after week 13, which is closer to how weight gain often behaves for many pregnancies.

When should I not use this calculator as my main guide?

If you have a multiple pregnancy, severe nausea and vomiting, diabetes, hypertension, preeclampsia risk, eating disorder history, or any condition where weight change is medically monitored, you should use clinician guidance as primary. Also, if you notice sudden rapid weight gain with swelling, headaches, or vision changes, treat that as a medical concern rather than a “normal” weight gain question.