Pregnancy Weight Gain Calculator
Enter pre-pregnancy height and weight and choose one baby or twins to see the published total range. Current week and weight are optional.
The weight-gain guide holds the full tables.
BMI category and published ranges
This page looks up a population weight-gain range from pre-pregnancy body mass index and from whether the pregnancy is one baby or twins. It does not date the pregnancy. If you need weeks and days first, use the Gestational Age Calculator. The weight-gain guide holds the full evidence tables; this page shows how the calculator selects a row and how to read it.
Body mass index is weight in kilograms divided by height in meters squared. The category uses the unrounded value: underweight below 18.5, normal weight from 18.5 to below 25, overweight from 25 to below 30, and obesity at 30 or above. A BMI of 40 or above stays in the obesity row for these ranges. The WHO fact sheet on obesity and overweight defines overweight as a BMI of 25 or above and obesity as a BMI of 30 or above in adults. The underweight boundary below 18.5 is the same cut point CDC pregnancy-weight guidance uses when it publishes gain ranges.
ACOG Committee Opinion 548 and the CDC page present the Institute of Medicine ranges from the National Academies 2009 report. For one baby those total ranges are 12.5–18 kg (28–40 lb) if underweight, 11.5–16 kg (25–35 lb) if normal weight, 7–11.5 kg (15–25 lb) if overweight, and 5–9 kg (11–20 lb) if obese. Twin totals on the CDC page are 22.7–28.1 kg (50–62 lb), 16.8–24.5 kg (37–54 lb), 14.1–22.7 kg (31–50 lb), and 11.3–19.1 kg (25–42 lb) for the same four categories. The underweight twin row is a CDC-published exception to the narrower set of twin ranges in the National Academies summary. No standard numeric range is assigned for triplets or more.
For a singleton pregnancy only, and only from 13 weeks 0 days through 40 weeks 0 days, the calculator can draw an optional week-specific band. It draws a straight line from a first-trimester reference of about 0.5–2.0 kg at 13 weeks 0 days to the BMI-specific total at 40 weeks 0 days. That line is a Pregnancy Metrics derivation. It is not an official CDC week-by-week curve, and the calculator does not assign a precise week-specific first-trimester target before 13 weeks. Published second- and third-trimester rates are shown as context. They are not a second cumulative formula.
Worked example
Height 165 cm and pre-pregnancy weight 60 kg. Height in meters is 1.65, and 1.65 squared is 2.7225. BMI = 60 ÷ 2.7225 = 22.0, which sits in the normal-weight row because it is at least 18.5 and below 25. For one baby the published total range is 11.5–16 kg (25–35 lb). The calculator classifies the unrounded BMI first and rounds the displayed BMI afterward, so a value that is just below a boundary stays in the lower category.
The same height and weight with twins uses the normal-weight twin total, 16.8–24.5 kg (37–54 lb), and does not draw the singleton weekly line. Adding a current weight shows how much has changed since the pre-pregnancy weight. A lower current weight is a valid entry. The calculator does not relabel that change as a diagnosis.
If the current week is 20 weeks 0 days in the singleton example, the optional band is the straight-line reference between the 13-week starting range and the 25–35 lb total at 40 weeks. It is a visual aid for that model. It is not a verdict that the pregnancy is “on track.”
How to read the range
Read the result as a span, not as a single target in the middle. People gain at different tempos. ACOG’s committee opinion and the ACOG patient answer on weight gain both describe the ranges as guidance that still has to be individualized. A number inside the span is consistent with the published range for that BMI and pregnancy type. A number outside it is a reason to look at the whole picture with a clinician. It is not, by itself, a diagnosis.
Use pre-pregnancy weight for the BMI. Weight measured after conception already includes pregnancy-related change, so it would sort you into a later category for the wrong reason. The optional local tracker stores entries in this browser only after you opt in. It is not a shared pregnancy record, and the Privacy Policy describes that storage.
NICE guideline NG247 covers maternal and child nutrition, including weight management. It is cited here because a BMI table is not a diet, a weight-loss plan, or a treatment. This calculator does not prescribe calories, supplements, or exercise.
Limits and clinical judgment
Talk with your prenatal clinician when the pregnancy is triplets or more, when the underweight twin range is the one that appeared, when gain is far from the published span, or when you have questions the table cannot see: nausea that limits eating, a history that changes the goal, or a concern about how you feel. The clinician’s advice replaces this population range for your care.
The calculator does not interpret swelling, blood pressure, glucose, fetal growth, or ultrasound measurements. Those are clinical assessments. Pregnancy weight gain is also a different measurement from a child’s growth after birth. Child Growth Lab is a separate site for that later question.
Frequently asked questions
- Why does pre-pregnancy BMI change the range?
The Institute of Medicine ranges, as published by CDC and discussed by ACOG, are different for underweight, normal weight, overweight, and obese categories. The same kilogram target is not applied to every starting BMI. The category describes the starting point. It is not a judgment about a body.
- Are twin ranges just double the singleton ranges?
No. The CDC publishes separate twin totals, and they are not twice the singleton totals. Triplets and higher-order pregnancies have no standard numeric range in these sources. Do not multiply either table.
- What is the weekly number?
For one baby, between 13 weeks 0 days and 40 weeks 0 days, it is this site’s straight-line reference from about 0.5–2.0 kg at the start of that span to the published total at 40 weeks. It is not an official CDC weekly band, and it is absent for twins and before 13 weeks.
- Can I track weights without an account?
The optional tracker stays in this browser after you turn it on. It is not uploaded as a pregnancy record. You can export a CSV locally. Clearing site data removes the entries.
Sources
These sources publish the ranges and the boundaries around them. They do not review or endorse Pregnancy Metrics.
- CDC — Weight Gain During Pregnancy. Singleton and twin total ranges by pre-pregnancy BMI, including the underweight twin range.
- ACOG Committee Opinion 548 — Weight Gain During Pregnancy. BMI-based ranges and individualized clinical judgment.
- National Academies — Weight Gain During Pregnancy: Reexamining the Guidelines. The 2009 evidence framework behind the ranges.
- WHO — Obesity and overweight. Adult BMI cut points of 25 for overweight and 30 for obesity.
- NICE guideline NG247 — Maternal and child nutrition. Nutrition and weight management in pregnancy, which a calculator range does not replace.