Pregnancy Weight Gain Calculator
Pregnancy Weight Gain Calculator
Find the recommended total weight gain for your pregnancy from your height and weight before pregnancy, for one baby or twins. Then check where your weight sits at any week against the range for that week, and see the weekly target, where the weight goes and the range at every week.
Recommended gain across the pregnancy
The ranges are the 2009 Institute of Medicine (now National Academy of Medicine) guidelines, as used by the CDC and ACOG. They depend on BMI before pregnancy, weight in kilograms divided by height in metres squared, rounded to one decimal, with cut points at 18.5, 25 and 30. For one baby the total gain is 28 to 40 lb below 18.5, 25 to 35 lb from 18.5 to 24.9, 15 to 25 lb from 25.0 to 29.9 and 11 to 20 lb at 30.0 and above. The sources print week by week guidance only as charts, so the band here is a straight line from the first trimester allowance of 1.1 to 4.4 lb at week 13 to the published total at week 40. Twins have provisional totals only. This tool gives general information and is not medical advice; if you are losing weight or gaining quickly, speak with your clinician, who sets your own goal. The CSV, image and printed report contain only the values you entered.
How to use this tool
Choose what to calculate. Recommended total gain takes your height, your weight before pregnancy and one baby or twins. Where you are at a given week adds the weeks and days you have reached and your weight now, and says whether your gain is inside, above or below the range for that week, and by how much. The other options give the weekly target, where the weight goes and the range at every week.
The input people most often get wrong is the starting weight. Gain counts from your weight before pregnancy, not today's, and entering today's weight hides your gain and can put you in the wrong BMI class. If you do not know it, use the earliest weight you have, such as your first prenatal visit. Count weeks from the first day of your last period, as your clinician does, and use one unit for both weights.
What the calculation is doing
The tool starts with your body mass index before pregnancy, which is weight in kilograms divided by height in metres squared. At 5 ft 5 in and 140 lb that is 63.5 kg divided by 1.651 m squared, or 23.3. Rounded to one decimal place, it falls in a class: below 18.5 is underweight, 18.5 to 24.9 normal weight, 25.0 to 29.9 overweight and 30.0 and above obese. These are the World Health Organization cut points, used by the 2009 Institute of Medicine report, now published by the National Academy of Medicine.
Each class has a recommended total for one baby: 28 to 40 lb (12.5 to 18 kg) for underweight, 25 to 35 lb (11.5 to 16 kg) for normal weight, 15 to 25 lb (7 to 11.5 kg) for overweight and 11 to 20 lb (5 to 9 kg) for obese. The kilograms are the report's own figures, rounded separately, so they differ from the pounds by at most 0.2 kg.
The report describes week by week guidance only in charts. It assumes 1.1 to 4.4 lb (0.5 to 2 kg) in the first trimester, then gain close to a straight line, averaging 1 lb a week for underweight and normal weight, 0.6 for overweight and 0.5 for obese. So the range for each week here is built from those points: a straight line from zero at week 0 to the allowance at week 13, then a straight line over 27 weeks to the published total at week 40.
For a week w from 14 to 40 the lower edge is 1.1 + (low total − 1.1) × (w − 13) ÷ 27 and the upper edge is 4.4 + (high total − 4.4) × (w − 13) ÷ 27. To place your weight, the tool subtracts your starting weight from your weight now, adds any extra days as a fraction of a week, and compares your gain with both edges to one decimal place. A gain exactly on an edge counts as inside.
Why your BMI sets the range
The Institute of Medicine committee worked from outcomes. For children it named size at birth, preterm birth and childhood obesity as the most important, and for mothers weight retained after the birth and unscheduled first cesarean delivery. It set a range for each BMI class, falling from 12.5 to 18 kg for underweight to 5 to 9 kg for obese, and said the range form reflects "the imprecision of the estimates on which the recommendations are based."
BMI is a ratio of weight to height and does not measure body composition. The report kept the standard cut points. In some Asian populations risks show up at lower BMI values, and a 2004 World Health Organization consultation identified action points at 23.0, 27.5, 32.5 and 37.5. If your clinician uses different cut points, follow their plan.
Why the first trimester is small and the later ones steady
The report notes that only some weight gain usually occurs in the first trimester, and that gain is greater and close to linear in the second and third. The baby, placenta, amniotic fluid, blood volume and uterus are small early on and grow later. The CDC adds that in general the first trimester does not require any extra calories. A pound or two either way at week 12 therefore means little.
The published rates and totals do not quite meet. For normal weight, 1.1 to 4.4 lb plus 0.8 to 1 lb a week for 27 weeks gives 22.7 to 31.4 lb at week 40, against a published total of 25 to 35 lb, a gap of 2.3 lb at the low end and 3.6 lb at the high end. The other classes agree within 1.7 lb. The sources do not say how the two were reconciled.
The tool anchors the band to the total, the figure the CDC and ACOG print, so for normal weight it widens at 0.89 to 1.13 lb a week against a published 0.8 to 1. The two constructions differ by at most 3.6 lb at any week.
Where the weight goes
Mayo Clinic's sample breakdown for a baby born at 7 to 8 lb is: baby 7 to 8 lb, fat stores 6 to 8, blood volume 3 to 4, body fluid 2 to 3, uterus 2, amniotic fluid 2, breast tissue 1 to 3 and placenta 1.5. That adds to 24.5 to 31.5 lb, or 28 lb at the midpoints. The baby is about a quarter of it and fat stores another quarter. MedlinePlus notes that much of the gain is not fat but is related to the baby.
Recommended gain by BMI class and week
The first table is the published guidance as printed. The second is the tool's range for one baby at each week, in pounds.
| BMI before pregnancy | Total, lb | Total, kg | Weekly, lb | Twins, lb |
|---|---|---|---|---|
| Underweight, below 18.5 | 28 to 40 | 12.5 to 18 | 1 (1 to 1.3) | none set |
| Normal weight, 18.5 to 24.9 | 25 to 35 | 11.5 to 16 | 1 (0.8 to 1) | 37 to 54 |
| Overweight, 25.0 to 29.9 | 15 to 25 | 7 to 11.5 | 0.6 (0.5 to 0.7) | 31 to 50 |
| Obese, 30.0 and above | 11 to 20 | 5 to 9 | 0.5 (0.4 to 0.6) | 25 to 42 |
Institute of Medicine 2009, summary table. Weekly gain is the average from week 14 to week 40 with its range in brackets. Twin totals are provisional.
| Week | Underweight | Normal weight | Overweight | Obese |
|---|---|---|---|---|
| 13 | 1.1 to 4.4 | 1.1 to 4.4 | 1.1 to 4.4 | 1.1 to 4.4 |
| 20 | 8.1 to 13.6 | 7.3 to 12.3 | 4.7 to 9.7 | 3.7 to 8.4 |
| 28 | 16 to 24.2 | 14.4 to 21.4 | 8.8 to 15.8 | 6.6 to 13.1 |
| 36 | 24 to 34.7 | 21.5 to 30.5 | 12.9 to 21.9 | 9.5 to 17.7 |
| 40 | 28 to 40 | 25 to 35 | 15 to 25 | 11 to 20 |
Recommended gain in pounds from the weight before pregnancy, one baby, as the tool draws it.
A worked example you can check on paper
Take the tool's defaults: 5 ft 5 in and 140 lb before pregnancy. Height is 65 in, or 1.651 m, and weight is 63.50 kg. BMI is 63.50 ÷ (1.651 × 1.651) = 63.50 ÷ 2.726 = 23.3, normal weight. The recommended total is 25 to 35 lb (11.5 to 16 kg), which puts your weight at term between 165 and 175 lb.
Now suppose you are at 24 weeks and weigh 153 lb. Your gain is 153 − 140 = 13 lb. The lower edge is 1.1 + (25 − 1.1) × (24 − 13) ÷ 27 = 1.1 + 23.9 × 11 ÷ 27 = 10.8 lb, and the upper edge is 4.4 + (35 − 4.4) × 11 ÷ 27 = 4.4 + 12.5 = 16.9 lb. A gain of 13 lb sits between them, 2.2 lb above the lower edge and 3.9 lb below the upper one, so it is inside the range. In kilograms the gain is 5.9 kg against a range of 5.0 to 7.7 kg.
Twins, and where these ranges stop applying
For twins the Institute gave provisional totals only: 37 to 54 lb (17 to 25 kg) for normal weight, 31 to 50 lb (14 to 23 kg) for overweight and 25 to 42 lb (11 to 19 kg) for obese. It found too little information for underweight, and the CDC lists 50 to 62 lb from a separate 2003 study. With no weekly range for twins, the tool compares your gain with the total. For triplets or more, the CDC says to talk to your provider.
The guidelines are intended for women in the United States and may apply in other developed countries, but not where women are substantially shorter or thinner or adequate obstetric services are unavailable. They describe population outcomes, not a prediction for one person. A CDC report cited on its page found that only about 1 in 3 women gained the recommended amount.
The guidance has not changed since 2009, and a 2026 National Academies workshop is weighing new evidence on whether to update it. This tool gives general information, not medical advice, and anyone who is losing weight, gaining quickly or worried about their weight should speak with their clinician.
Mistakes that catch people out
Using today's weight as the starting weight. Your gain then reads as zero and your BMI class can change. Use the earliest weight you have.
Mixing units. Inches in the centimetres box, or kilograms with the units set to pounds. The tool flags values out of range, but a slip that lands in range gives a plausible wrong answer.
Counting weeks from conception. Clinicians date pregnancy from the last period, so 22 weeks from conception is usually called 24. Use the number on your prenatal paperwork.
Treating the weekly figure as a target for every week. Gain is uneven, and one quiet or busy week tells you little.
Reading one weighing as a verdict. Fluid, clothing and the scale move the number. Compare the pattern across visits, then let your clinician interpret it.
Popular calculations
Each opens the calculator with its own address, and every value can be changed once it is open.
Total gain by BMI class, one baby
Where you are at week 12, 20, 28 and 36
Weekly target
Twins
Where the weight goes, and the week by week table
How this was checked
The engine was tested in Node against the summary table of the 2009 report, typed in a second time, for pounds, kilograms, twins and the first trimester figure. The same pound totals appear on the CDC page, in ACOG Committee Opinion 548 and in NICHD and Mayo Clinic guidance. The band matched a separate piecewise line at 1,288 points to within 7 × 10−15 lb and equals the published total at week 40. Boundaries at BMI 18.5, 25 and 30 were tested, including 18.45, 24.95 and 29.95, which round up.
One inconsistency turned up: the CDC row for the top class is labelled BMI 30.0 to 39.9, while the Institute table and ACOG say 30 and above. The tool follows the Institute. Every address above was opened and checked for a distinct title, the right answer, charts that render and exports containing only what was entered.
Common questions
How much weight should I gain during pregnancy?
It depends on your BMI before pregnancy. For one baby the 2009 Institute of Medicine guidance is 28 to 40 lb below BMI 18.5, 25 to 35 lb from 18.5 to 24.9, 15 to 25 lb from 25.0 to 29.9 and 11 to 20 lb at 30.0 and above. In kilograms that is 12.5 to 18, 11.5 to 16, 7 to 11.5 and 5 to 9. Your clinician sets your own goal.
How much weight should I gain each week?
About 1.1 to 4.4 lb (0.5 to 2 kg) in total for the first trimester, then an average from week 14 of 1 lb a week for underweight, 1 lb (range 0.8 to 1) for normal weight, 0.6 lb (0.5 to 0.7) for overweight and 0.5 lb (0.4 to 0.6) for obese. These are averages over many weeks, and real gain is uneven.
How much weight gain is normal in the first trimester?
The Institute of Medicine assumed 1.1 to 4.4 lb (0.5 to 2 kg) across weeks 1 to 13. MedlinePlus gives 2 to 4 lb, NICHD about 1 to 4 lb, and the CDC notes the first trimester generally needs no extra calories. A pound or two either side at week 12 means little on its own.
How much should I have gained by week 20 or week 28?
For normal weight and one baby the tool draws 7.3 to 12.3 lb at week 20 and 14.4 to 21.4 lb at week 28. For overweight it is 4.7 to 9.7 lb and 8.8 to 15.8 lb. The sources print week by week guidance only as charts, so these are straight line figures between published points.
How much weight should I gain with twins?
The Institute of Medicine gave provisional totals: 37 to 54 lb (17 to 25 kg) for normal weight, 31 to 50 lb (14 to 23 kg) for overweight and 25 to 42 lb (11 to 19 kg) for obese. It set none for underweight, and the CDC lists 50 to 62 lb from a separate study. There is no published weekly range for twins.
What if my gain is above or below the range?
One weighing says little, since fluid, clothing and the scale all move the number. If your gain stays above or below the range across visits, mention it to your clinician. ACOG says individualized care and clinical judgment are needed for overweight or obese women who gain less than recommended while the baby is growing appropriately.
Related Calculators and Reference
- Due Date Calculator: your due date and weeks reached.
- BMI Calculator: body mass index and its standard classes.
- Ovulation Calculator: fertile days, if you are planning ahead.
- TDEE Calculator: a general daily calorie estimate.
- Water Intake Calculator: a general estimate of daily fluid.
- CDC: Weight Gain During Pregnancy: the ranges for one baby and for twins.