Enter your pre-pregnancy height and weight plus your current week — see your BMI category, total recommended gain range, and gain-to-date target.
There is no single healthy figure, and that is the most useful thing to know about this subject. The widely used guidelines set a different total range for each starting BMI category, on the reasoning that someone beginning underweight has different needs from someone beginning above the healthy range:
| Pre-pregnancy BMI | Category | Recommended total gain |
|---|---|---|
| Under 18.5 | Underweight | 28–40 lb |
| 18.5 – 24.9 | Normal | 25–35 lb |
| 25.0 – 29.9 | Overweight | 15–25 lb |
| 30.0 and over | Obese | 11–20 lb |
The ranges narrow as starting BMI rises, and every one of them is a range rather than a target. The figure the calculator asks for is your weight before pregnancy — using current weight partway through shifts you into the wrong category and produces a recommendation built for someone else.
The pacing matters as much as the total. First-trimester gain is small — commonly around 1 to 4 lb across the whole of the first 13 weeks, and some people lose weight during it if nausea is significant. Most of the gain happens steadily through the second and third trimesters.
This is why the calculator asks which week you are in and gives a range for that point rather than only a final figure. It models roughly 2 lb over the first trimester and then distributes the remainder evenly across the weeks that follow, which is a simplification of a curve that is not perfectly linear in reality, but tracks the intended shape.
Worth knowing, because it makes clear that the gain is mostly not fat. At term a typical distribution runs roughly: the baby around 7–8 lb, the placenta 1–2 lb, amniotic fluid about 2 lb, an enlarged uterus about 2 lb, extra blood volume 3–4 lb, additional fluid 2–3 lb, and increased breast tissue 1–3 lb. Maternal fat stores make up the balance, and those exist deliberately — they are the reserve the body draws on for the final weeks and for feeding afterwards.
Weight tracking in pregnancy is a screening signal, and the honest framing is that a reading outside the band is a prompt to raise it with your midwife or doctor, not a problem to solve alone. Gaining faster or slower than expected can have entirely benign explanations — fluid retention, a growth spurt, an easing of early nausea, or simply a different scale.
What matters more than any single reading is the trend across several weeks, and that a clinician who knows your history is the one interpreting it. Do not restrict intake to hit a number on this page.
These figures do not apply to twins or higher multiples, which carry substantially higher recommended ranges and are outside what this tool models. They also assume a single, uncomplicated pregnancy; conditions such as gestational diabetes, hyperemesis or pre-eclampsia change the picture and are managed individually.
This is general information based on published guidance, not medical advice, and it is no substitute for antenatal care. Your week of pregnancy and pre-pregnancy BMI are the two inputs it depends on, so both are worth getting right.
The Institute of Medicine (IOM) recommends total gain ranges based on your pre-pregnancy BMI, for a single-baby pregnancy carried to term: 28-40 lbs if underweight (BMI under 18.5), 25-35 lbs if normal weight (18.5-24.9), 15-25 lbs if overweight (25-29.9), and 11-20 lbs if obese (30+). This calculator estimates roughly 2 lbs of that total by week 13, then spreads the remainder evenly across weeks 14-40.
Yes — the IOM guidelines are explicitly tiered by pre-pregnancy BMI category, with a lower starting weight linked to a higher recommended total gain and a higher starting weight linked to a lower one. This calculator computes your pre-pregnancy BMI first (the same formula as the BMI Calculator) to select the right range automatically.
Individual pregnancies vary, and short-term fluctuations week to week are normal — this calculator gives a general population-level guideline, not a diagnosis or a strict target. If you're consistently outside the recommended range over several weeks, talk to your doctor or midwife, who can factor in your specific health history, nutrition, and how the pregnancy is progressing.
No — the IOM sets separate, higher weight gain guidelines for twin and other multiple pregnancies, reflecting the additional physiological demands of carrying more than one baby. This calculator uses the singleton (single-baby) ranges only, so expecting parents of twins or multiples should get guidance specific to their pregnancy from their provider rather than relying on this tool.
Worked example: pre-pregnancy height 165 cm, weight 67 kg: BMI = 67 ÷ 1.65² ≈ 24.6, which falls in the Normal category (25-35 lbs total recommended). By week 20 — 7 weeks into the second-trimester phase after week 13 — the gain-to-date estimate is roughly 2 + (23 × 7÷27) to 2 + (33 × 7÷27) ≈ 8.0-10.6 lbs.
Tracking your due date too? See the Pregnancy Due Date Calculator or check your BMI Calculator result directly. Gain guidance is published in pounds in the US and kilograms almost everywhere else; the kg to pounds converter reconciles the two.