Free Pregnancy Weight Gain Calculator

Estimate healthy pregnancy weight gain based on your pre-pregnancy BMI and current week. Uses 2009 Institute of Medicine guidelines (singleton + twin pregnancies).

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5'4" = 64 inches.

Different IOM guidelines apply for twin pregnancies.

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Enter your details on the left, then press Calculate.

What is this calculator for?

You're 22 weeks pregnant, you've gained 14 pounds, your OB hasn't said anything either way, and you're trying to figure out if that's appropriate. Or you're early in pregnancy and want to know what total weight gain to expect across nine months so you can plan psychologically and clothing-wise. Pregnancy weight gain has a wide normal range, but specific targets exist based on your pre-pregnancy BMI — recommendations from the Institute of Medicine that almost every US obstetrician uses.

IOM/NAM 2009 guidelines for total pregnancy weight gain by pre-pregnancy BMI: Underweight (BMI <18.5): 28-40 lbs total. Normal weight (BMI 18.5-24.9): 25-35 lbs. Overweight (BMI 25-29.9): 15-25 lbs. Obese (BMI 30+): 11-20 lbs. Twin pregnancy: add 10-12 lbs to the above. These ranges are designed to balance fetal growth, maternal health, and post-pregnancy weight retention.

This calculator takes your pre-pregnancy weight and height, your current pregnancy week, and your current weight, and computes whether your gain so far is on track. It outputs the recommended range for your full pregnancy, your current-week-target range, and the gap (if any) between where you are and the expected range.

How to use this calculator

Enter your pre-pregnancy weight (the weight you were at conception, or as close as you can estimate). Enter your height. The calculator computes pre-pregnancy BMI and assigns the IOM range for total recommended gain.

Enter your current pregnancy week (or due date — the calculator can derive week from due date). Most pregnancies are tracked from last menstrual period (LMP) — week 1 = LMP week. By week 12 you've completed the first trimester; by week 28, the second; full term is weeks 37-42.

Enter your current weight. The calculator subtracts pre-pregnancy weight to derive gain to date. It then compares to the expected gain at this week.

The calculator outputs total recommended gain, your current gain, where you should be at this week, and a green/yellow/red status: green for within range, yellow for outside range but not concerning, red for significantly outside (consult OB).

Understanding your results

The calculator returns your total recommended weight gain range for your pre-pregnancy BMI, your current gain, the expected gain for your current week, and the gap.

How to read it. Weight gain in pregnancy isn't linear. First trimester (weeks 1-13): typically 1-5 lbs total (some women lose 0-2 lbs due to nausea — normal). Second trimester (14-27): roughly 1 lb/week for normal-BMI women. Third trimester (28-40): roughly 1 lb/week, sometimes slowing in final weeks. So at week 22 for a normal-BMI woman: expected gain is 5 lbs (first trimester) + 8 lbs (second trimester through week 22) = 13 lbs. The range around this is wide; 8-18 lbs at week 22 would all be in normal-trajectory territory.

Where the weight goes. Roughly: baby 7-8 lbs, placenta 1-2 lbs, amniotic fluid 2 lbs, uterus growth 2 lbs, breasts 1-3 lbs, increased blood volume 3-4 lbs, increased fluid 2-3 lbs, fat stores 5-9 lbs. Total accounts for about 25-30 lbs of the recommended gain. Women who gain at the high end of recommendations typically have more fat stores; gain at the low end means leaner gain.

Gaining too little. Gain below the recommended range increases risk of low birth weight, preterm delivery, and developmental issues. If your gain is significantly below trajectory and not due to morning sickness in early pregnancy, your OB should evaluate — common causes include hyperemesis gravidarum (severe morning sickness), restrictive eating disorder, or rare medical conditions affecting absorption.

Gaining too much. Excess gain above the recommended range increases risk of gestational diabetes, hypertension, large-for-gestational-age baby, cesarean delivery, and post-pregnancy weight retention. The strongest predictor of post-pregnancy weight retention 5+ years later is total pregnancy weight gain — women who gain at the high end of the range or above carry more weight long-term than those who gain at the low end.

Per-week gain interpretation. Sudden gains of 2+ lbs in a single week, especially in the second or third trimester, can indicate fluid retention from preeclampsia — a serious complication. Call your OB the same day if you experience sudden weight jump combined with swelling, headache, vision changes, or upper abdominal pain.

A worked example

Aisha is 28, 5'5", was 142 lbs pre-pregnancy (BMI 23.6 — normal weight). She's now 22 weeks pregnant and weighs 156 lbs — total gain 14 lbs to date.

IOM target for normal-BMI: 25-35 lbs total over 40 weeks. Expected gain by week 22: roughly 5 lbs first trimester + (22−13) × 1 lb/week = 14 lbs. Aisha's gain at 14 lbs is right on the expected curve — within the recommended trajectory.

Projection to full term (week 40): if she continues at ~1 lb/week through week 40, she'll gain another 18 lbs (weeks 22-40), reaching 32 lbs total. Within the 25-35 lb target. Her OB confirms at her 24-week visit that everything looks normal.

Variation: same Aisha at week 22 but weighs 162 lbs (20 lbs gained). Six pounds above the expected 14. Trajectory at this rate to week 40: 20 + 18 = 38 lbs total — above the 25-35 range. Her OB notes the higher gain, discusses diet and activity, and recommends moderate adjustment — not aggressive restriction (pregnancy is not the time for caloric deficits), but mindful eating without trying to "eat for two" (the actual extra calorie need is only 300-450 cal/day in second and third trimesters). She moderates intake and slows gain to about 0.7 lb/week through the rest of pregnancy, ending at 34 lbs — within range.

Variation: pre-pregnancy obese-BMI scenario. Maria, 32, 5'6", 198 lbs pre-pregnancy (BMI 32 — obese). IOM target: 11-20 lbs total. At week 22 she's gained 7 lbs. Expected for obese-BMI at week 22: about 5-7 lbs (slower trajectory than normal-BMI). She's on track. Projection to week 40: continuing at ~0.5 lb/week from here would add 9 lbs, totaling 16 lbs — within the 11-20 range. Some obese women actually lose weight in early pregnancy (1-3 lbs) and still have healthy outcomes — the body has fat reserves to draw from. The IOM ranges reflect this physiology.

Related resources

For tracking pregnancy progress and milestones, see Pregnancy Week Calculator and Due Date Calculator. For nutrition planning during pregnancy, the Calorie Calculator (with the standard pregnancy add-ons) and Macro Calculator. For broader body composition context, BMI Calculator. The American College of Obstetricians and Gynecologists (ACOG) publishes the authoritative clinical guidelines on pregnancy nutrition and weight gain; the 2009 IOM report is the source for the BMI-based weight gain ranges.

Related calculators

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Frequently asked questions

Is it normal to lose weight in the first trimester?

Yes, mild weight loss in the first trimester is common, especially with morning sickness. Up to 5% of pre-pregnancy weight loss is generally not concerning if you're eating and drinking enough to stay hydrated. Severe vomiting (hyperemesis gravidarum) affecting 1–3% of pregnancies needs medical management. By week 13–14, most women have either maintained or gained 1–4.5 lbs.

How much weight should I gain with twins?

Significantly more than with a singleton. IOM recommends: normal-BMI women carrying twins should gain 37–54 lbs total (vs. 25–35 for one baby); overweight 31–50 lbs (vs. 15–25); obese 25–42 lbs (vs. 11–20). Twin pregnancies don't have specific guidelines for underweight BMI because data is limited. Weekly gain rates in trimesters 2 and 3 are about 1.1–1.4 lbs/week for normal-BMI twin pregnancies.

When should I talk to my doctor about weight gain?

Always when: gaining more than 3 lbs in a single week after week 20 (possible preeclampsia warning), losing weight in the 2nd or 3rd trimester, gaining less than 0.5 lb/week consistently after week 20, or significantly outside the recommended range. Don't try to lose weight while pregnant unless directed — even women with high pre-pregnancy BMI should still gain some weight for fetal development.

Why is recommended weight gain different based on pre-pregnancy BMI?

Women with lower pre-pregnancy BMI have less fat reserve and need to gain more to support fetal growth. Women with higher pre-pregnancy BMI have substantial fat reserves and gain less while still supporting healthy fetal development. The IOM ranges balance several risks: too little gain in any category risks low birth weight and developmental issues; too much gain risks gestational diabetes, hypertension, and post-pregnancy weight retention. The lower targets for higher BMI categories reflect that obesity at conception is already associated with elevated risks; further weight gain compounds them.

Can I lose weight during pregnancy if I'm overweight or obese?

Intentional weight loss during pregnancy is generally not recommended — the focus should be on healthy nutrition and appropriate gain within your IOM range. However, some obese women naturally lose 1-3 lbs in early pregnancy due to nausea or reduced appetite, and this is typically not concerning. Targeted caloric restriction during pregnancy can interfere with fetal nutrient supply. The right strategy for obese women: aim for the lower end of the 11-20 lb range, eat nutrient-dense foods, moderate physical activity (with OB approval), and focus on post-pregnancy weight management rather than pregnancy weight loss.

How much extra should I eat during pregnancy?

Far less than 'eating for two' suggests. First trimester: no extra calories needed (just standard maintenance — your TDEE doesn't change much, and most women have nausea reducing appetite anyway). Second trimester: +340 cal/day above pre-pregnancy maintenance. Third trimester: +450 cal/day. A 340-cal increase is one extra snack — a banana with peanut butter, or a yogurt with granola. The 'eating for two' folk wisdom dramatically overstates pregnancy calorie needs and is one of the most common drivers of excess gain.

What if I gain too much weight during pregnancy?

First, don't panic — excess gain is correctable, and gestational outcomes depend on many factors beyond weight alone. Second, talk to your OB about modifying diet and activity. Strategies: focus on nutrient-dense foods (lean protein, vegetables, whole grains), reduce empty calories (sweetened drinks, processed snacks, fast food), incorporate appropriate moderate exercise like walking or pregnancy yoga (with OB approval). Don't crash diet — caloric restriction during pregnancy can interfere with fetal development. The goal is to slow further gain, not reverse existing gain. Most women who exceed recommendations can still have healthy outcomes; the focus shifts to managing risks like glucose screening and BP monitoring.

How much weight will I lose immediately after delivery?

Typically 10-13 lbs in the first few days postpartum, accounting for baby (~7.5 lbs), placenta (1-2 lbs), amniotic fluid (~2 lbs), and immediate fluid loss. Over the next 6 weeks, additional 5-15 lbs from continued fluid loss, uterine contraction, and breast/blood volume normalization. The remaining weight (typically 5-15 lbs for normal-BMI women who gained within range) is fat stores and tissue gain — this loses over months with normal post-pregnancy activity and breastfeeding (which burns ~500 extra cal/day). Most women return to within 5 lbs of pre-pregnancy weight by 6-12 months postpartum if they gained within IOM range. Those who gained excess often retain more weight long-term.

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