Pregnancy Weight Gain Calculator
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Results
Pre-pregnancy BMI 23.3 (healthy weight): recommended total gain 25–35 lb. Gain so far 10 lb at week 20: within the range (7.3–12.3 lb).
| Week | Gain so far (lb) | Weight (lb) |
|---|---|---|
| 2 | 0.2–0.7 | 140.2–140.7 |
| 4 | 0.3–1.4 | 140.3–141.4 |
| 6 | 0.5–2 | 140.5–142 |
| 8 | 0.7–2.7 | 140.7–142.7 |
| 10 | 0.8–3.4 | 140.8–143.4 |
| 12 | 1–4.1 | 141–144.1 |
| 14 | 2–5.5 | 142–145.5 |
| 16 | 3.8–7.8 | 143.8–147.8 |
| 18 | 5.5–10.1 | 145.5–150.1 |
| 20 | 7.3–12.3 | 147.3–152.3 |
The IOM gives totals and weekly rates, not week-by-week targets. The by-week figures assume 1.1–4.4 lb gained by week 13, as the IOM does, then a steady gain to the total range at 40 weeks.
This is an estimate based on the IOM 2009 guidelines, not medical advice. Gain varies from week to week, partly with fluid, and many things affect what is right for you. Talk to your doctor or midwife and follow their advice.
How to use the pregnancy weight gain calculator
- Choose US units (feet, inches and pounds) or metric at the top.
- Enter your height and your weight before this pregnancy, and whether you are expecting one baby or twins.
- Optionally, enter how many weeks pregnant you are and your weight now to see where your gain sits against the suggested range for that week.
How the ranges are worked out
BMI category → IOM 2009 total gain range
gain by week w ≤ 13 = (w ÷ 13) × first-trimester gain
gain by week w > 13 = first-trimester gain + (w − 13) ÷ 27 × (total − first-trimester gain)
The IOM, now the National Academy of Medicine, set its 2009 guidelines by pre-pregnancy BMI using the WHO categories. Each category has a total range for a full-term pregnancy and a weekly rate for the second and third trimesters, with the calculations assuming 1.1–4.4 lb (0.5–2 kg) gained in the first trimester. The IOM does not publish week-by-week targets, so the by-week band here is an interpolation: it rises steadily to the first-trimester range at week 13, then steadily to the total range at week 40. For twins, the IOM gives provisional totals only.
Worked example
Before pregnancy you were 5 ft 5 in and 140 lb, a BMI of 23.3 (healthy weight). The IOM range for one baby is 25–35 lb in total, about 0.8 to 1 lb a week in the second and third trimesters. At 20 weeks the suggested gain so far is 7.3–12.3 lb, so weighing 150 lb (a 10 lb gain) is within the range. With twins, the provisional range would be 37–54 lb.
IOM 2009 weight gain guidelines
| Before pregnancy | BMI | Total gain (lb) | Total gain (kg) | Weekly, 2nd and 3rd trimesters | Twins (provisional) |
|---|---|---|---|---|---|
| Underweight | Below 18.5 | 28–40 | 12.5–18 | 1–1.3 lb (0.44–0.58 kg) | No IOM guideline |
| Healthy weight | 18.5 to 24.9 | 25–35 | 11.5–16 | 0.8–1 lb (0.35–0.5 kg) | 37–54 lb (17–25 kg) |
| Overweight | 25 to 29.9 | 15–25 | 7–11.5 | 0.5–0.7 lb (0.23–0.33 kg) | 31–50 lb (14–23 kg) |
| Obesity | 30 or more | 11–20 | 5–9 | 0.4–0.6 lb (0.17–0.27 kg) | 25–42 lb (11–19 kg) |
The IOM found too little information to set a twin range for people who are underweight before pregnancy.
Suggested gain by week (one baby, pounds)
Cumulative gain from the interpolated band, by pre-pregnancy BMI category.
| Week | Underweight | Healthy weight | Overweight | Obesity |
|---|---|---|---|---|
| 8 | 0.7–2.7 | 0.7–2.7 | 0.7–2.7 | 0.7–2.7 |
| 13 | 1.1–4.4 | 1.1–4.4 | 1.1–4.4 | 1.1–4.4 |
| 16 | 4.1–8.4 | 3.8–7.8 | 2.6–6.7 | 2.2–6.1 |
| 20 | 8.1–13.6 | 7.3–12.3 | 4.7–9.7 | 3.7–8.4 |
| 24 | 12.1–18.9 | 10.8–16.9 | 6.8–12.8 | 5.1–10.8 |
| 28 | 16–24.2 | 14.4–21.4 | 8.8–15.8 | 6.6–13.1 |
| 32 | 20–29.5 | 17.9–25.9 | 10.9–18.9 | 8.1–15.4 |
| 36 | 24–34.7 | 21.5–30.5 | 12.9–21.9 | 9.5–17.7 |
| 40 | 28–40 | 25–35 | 15–25 | 11–20 |
Keeping the numbers in perspective
- Ranges, not targets. The IOM framed its guidelines as ranges because good outcomes happen across a range of gains, and it asked clinicians to use them with clinical judgment.
- Week-to-week changes are normal. Fluid, meals and the time of day all shift the scale. Look at the trend over several weeks rather than one reading.
- Early pregnancy is different. Some people gain little or even lose weight in the first trimester, especially with nausea; the band starts small for that reason.
- Your care team sees the whole picture. They consider your health, the baby's growth and your history before suggesting any change, so bring questions to your appointments rather than dieting or eating more on your own.
The BMI used here is your pre-pregnancy BMI; BMI is not used to judge weight during pregnancy. This is not medical advice; talk to your doctor or midwife. To check your dates, use the pregnancy calculator, or see the BMI calculator for adult BMI categories.
Sources
- Institute of Medicine and National Research Council, Weight Gain During Pregnancy: Reexamining the Guidelines, Washington, DC: National Academies Press, 2009 (Summary, Table S-1).
- CDC, Weight Gain During Pregnancy (May 15, 2024).
Frequently asked questions
How much weight should I gain during pregnancy?
It depends on your BMI before pregnancy. For one baby, the IOM 2009 guidelines are 28–40 lb (12.5–18 kg) if underweight, 25–35 lb (11.5–16 kg) at a healthy weight, 15–25 lb (7–11.5 kg) if overweight and 11–20 lb (5–9 kg) with obesity. Your care provider may advise differently.
How much weight should I gain each week?
After the first trimester, the IOM suggests about 1 to 1.3 lb a week if underweight, 0.8 to 1 lb at a healthy weight, 0.5 to 0.7 lb if overweight and 0.4 to 0.6 lb with obesity. In metric, that is 0.44–0.58, 0.35–0.50, 0.23–0.33 and 0.17–0.27 kg a week.
How much weight should I gain with twins?
The IOM’s provisional twin ranges at term are 37–54 lb (17–25 kg) at a healthy pre-pregnancy weight, 31–50 lb (14–23 kg) if overweight and 25–42 lb (11–19 kg) with obesity. It found too little information to set a range for people who are underweight.
How much weight should I have gained by 20 weeks?
The IOM gives totals and weekly rates rather than week-by-week targets. Interpolating them, a person at a healthy weight before pregnancy would have gained roughly 7.3 to 12.3 lb by 20 weeks, assuming 1.1 to 4.4 lb in the first trimester.
What if my weight gain is outside the range?
Being above or below the range at one point is not a diagnosis; gain varies from week to week. Mention it to your doctor or midwife, who can look at your health and the baby’s growth before suggesting any change.