One of the first questions you'll have after seeing that positive pregnancy test — right after "when is my due date?" — is how much weight you should actually gain over the next nine months. It's a question that sounds simple but gets surprisingly complicated fast. Gain too little and you risk preterm birth or a low-birth-weight baby. Gain too much and you increase your chances of gestational diabetes, cesarean delivery, and postpartum weight retention.
The good news is that decades of research have produced clear, evidence-based guidelines tailored to your pre-pregnancy body mass index. The Institute of Medicine (IOM) published its most recent recommendations in 2009, and they remain the gold standard used by obstetricians and midwives today. A large 2025 BMJ study analyzing 1.6 million pregnancies reconfirmed that staying within these ranges leads to the best outcomes for both mother and baby.
This guide walks you through exactly how much weight to expect week by week, where that weight actually goes, what to do if you're above or below the target, and how to stay on track without obsessing over the scale. Track your progress with our Pregnancy Weight Gain Calculator.
How Much Total Weight Should You Gain?
Your recommended total weight gain depends on your pre-pregnancy BMI. The IOM guidelines — endorsed by the American College of Obstetricians and Gynecologists (ACOG) and still the standard of care — break it down like this:
| Pre-Pregnancy BMI | BMI Range | Recommended Total Gain | Weekly Rate (2nd & 3rd Tri) |
|---|---|---|---|
| Underweight | Below 18.5 | 28–40 lbs (12.7–18.1 kg) | ~1.0 lb/week |
| Normal weight | 18.5–24.9 | 25–35 lbs (11.3–15.9 kg) | ~1.0 lb/week |
| Overweight | 25.0–29.9 | 15–25 lbs (6.8–11.3 kg) | ~0.6 lb/week |
| Obese | 30.0 or higher | 11–20 lbs (5.0–9.1 kg) | ~0.5 lb/week |
These ranges aren't arbitrary. They're based on large-scale studies tracking outcomes like birth weight, cesarean rates, preterm delivery, and postpartum weight retention. Not sure what your BMI is? You can check it quickly with our BMI Calculator using your pre-pregnancy weight and height.
One important note: these guidelines are for singleton pregnancies. If you're carrying twins, the numbers change significantly (more on that below).
Where Does the Weight Actually Go?
If your target is 25–35 pounds, you might wonder where all that weight ends up — especially since the average newborn weighs only about 7.5 pounds. Here's the approximate breakdown for a woman who gains 30 pounds during a normal-weight pregnancy:
The takeaway? About 65% of your pregnancy weight gain has nothing to do with fat. Your blood volume nearly doubles, your uterus grows from the size of a pear to the size of a watermelon, and your body strategically stores fluid and energy reserves to support labor, delivery, and breastfeeding. Understanding this breakdown can help ease the anxiety that sometimes comes with watching the number on the scale climb.
First Trimester: Weeks 1–12
During the first trimester, weight gain is minimal — and for some women, the scale might not move at all. The general target is 1–5 pounds total over the first 12 weeks, regardless of your pre-pregnancy BMI.
There are a few reasons the gain is so small early on. Your baby is still microscopic for most of this period — by week 12, the fetus weighs only about half an ounce. The placenta is forming but still tiny. Most of the early changes are happening at the cellular and hormonal level, not in ways that register on a bathroom scale.
If you're dealing with morning sickness (which affects up to 80% of pregnant women), you might actually lose a few pounds in the first trimester. That's perfectly normal and usually not a concern unless the vomiting is severe enough to cause dehydration — a condition called hyperemesis gravidarum that affects about 1–3% of pregnancies and requires medical attention.
Week-by-week snapshot (first trimester)
- Weeks 1–4: Little to no change. Most women don't even know they're pregnant yet.
- Weeks 5–8: Hormonal shifts begin. Nausea may suppress appetite. Weight change: 0–1 lb.
- Weeks 9–12: Appetite may start to stabilize. Blood volume begins increasing. Weight change: 1–4 lbs cumulative.
Don't stress if your first-trimester gain doesn't follow a neat pattern. The body has plenty of time to catch up in the second trimester, and your healthcare provider will monitor your overall trajectory rather than any single weigh-in.
Second Trimester: Weeks 13–26
The second trimester is when most of the visible weight gain begins. Morning sickness typically eases, appetite returns (sometimes with a vengeance), and your baby enters a rapid growth phase. This is the trimester where steady, consistent gain matters most.
For women with a normal pre-pregnancy BMI, the target is roughly 1 pound per week during the second and third trimesters. For overweight women, that drops to about 0.6 pounds per week. For underweight women, it's closer to 1–1.3 pounds per week.
Week-by-week snapshot (second trimester)
- Weeks 13–16: Baby is growing from the size of a peach to an avocado. You may notice your regular clothes getting tight. Cumulative gain: 4–8 lbs.
- Weeks 17–20: The halfway point. Your baby weighs about 10 ounces by week 20, and you're likely showing. Many women notice the most dramatic jump in gain around week 20. Cumulative gain: 8–14 lbs.
- Weeks 21–26: Your baby's weight roughly triples during this stretch. Blood volume continues expanding. You may notice swelling in your hands and feet. Cumulative gain: 12–20 lbs.
This is also a good time to calculate your due date if you haven't already, so you can map your remaining weight gain trajectory against the weeks you have left.
Third Trimester: Weeks 27–40
The final stretch is when your baby packs on the most weight — growing from about 2 pounds at week 27 to 6–9 pounds at delivery. Your body continues adding blood volume, amniotic fluid, and energy reserves. The weekly gain rate stays roughly the same as the second trimester, though many women notice it slowing down slightly in the final 2–3 weeks before delivery.
Week-by-week snapshot (third trimester)
- Weeks 27–30: Baby is gaining about half a pound per week. You're likely gaining 0.8–1.0 lb/week if you started at a normal weight. Cumulative gain: 17–24 lbs.
- Weeks 31–35: Baby's brain is developing rapidly, and fat stores are accumulating under the skin. You may feel heavier and more uncomfortable. Cumulative gain: 22–30 lbs.
- Weeks 36–40: Growth slows slightly. Many women gain 0.5–1.0 lb/week in these final weeks. Some women even lose a pound or two right before labor as the body sheds water weight. Cumulative gain: 25–35 lbs.
By the end of the third trimester, roughly half of your total weight gain is baby, placenta, and amniotic fluid. The other half is the support system your body built — extra blood, breast tissue, uterine muscle, and energy stores.
Worked Example: Normal-Weight Pregnancy
Let's follow Sarah through her pregnancy. She's 29 years old, 5'6" (167 cm), and weighed 140 pounds pre-pregnancy. Her BMI is 22.6 — solidly in the normal range.
Her target: 25–35 pounds total, with about 1 pound per week in the second and third trimesters.
| Milestone | Week | Expected Weight | Actual Weight |
|---|---|---|---|
| Pre-pregnancy | — | 140 lbs | 140 lbs |
| End of 1st trimester | 12 | 143 lbs (+3) | 142 lbs (+2) |
| Midpoint | 20 | 151 lbs (+11) | 152 lbs (+12) |
| End of 2nd trimester | 26 | 157 lbs (+17) | 158 lbs (+18) |
| Week 32 | 32 | 163 lbs (+23) | 164 lbs (+24) |
| Week 36 | 36 | 167 lbs (+27) | 168 lbs (+28) |
| Delivery | 40 | 170 lbs (+30) | 171 lbs (+31) |
Sarah's actual gain of 31 pounds falls right in the middle of her 25–35 pound target range. She gained a bit more than expected in the second trimester but evened out by the end. Her provider was never concerned because her overall trajectory stayed within the recommended range.
Worked Example: Overweight Pre-Pregnancy BMI
Now let's follow Maria. She's 33, 5'4" (163 cm), and weighed 170 pounds before pregnancy. Her BMI is 29.2 — in the overweight category.
Her target: 15–25 pounds total, with about 0.6 pounds per week in the second and third trimesters.
| Milestone | Week | Expected Weight | Actual Weight |
|---|---|---|---|
| Pre-pregnancy | — | 170 lbs | 170 lbs |
| End of 1st trimester | 12 | 173 lbs (+3) | 171 lbs (+1) |
| Midpoint | 20 | 178 lbs (+8) | 177 lbs (+7) |
| End of 2nd trimester | 26 | 182 lbs (+12) | 181 lbs (+11) |
| Week 32 | 32 | 185 lbs (+15) | 186 lbs (+16) |
| Week 36 | 36 | 188 lbs (+18) | 189 lbs (+19) |
| Delivery | 40 | 190 lbs (+20) | 191 lbs (+21) |
Maria gained 21 pounds — right in the middle of her 15–25 pound range. Notice how her weekly gain rate was notably slower than Sarah's, and that's exactly what the guidelines recommend. Despite the lower total gain, her baby was born at a healthy 7 lbs 6 oz.
What If You're Gaining Too Much or Too Little?
Weight gain rarely follows a perfectly smooth line. A week of holiday eating, a bout of stomach flu, or increased water retention can all cause temporary spikes or dips. Your provider looks at the overall trend, not individual weigh-ins. That said, a consistent pattern of over- or under-gaining deserves attention.
Gaining More Than Recommended
Excessive weight gain increases your risk of gestational diabetes, preeclampsia, cesarean delivery, and having a baby that's large for gestational age (macrosomia). It also makes postpartum weight loss harder.
If you're consistently above target, focus on these adjustments. Replace calorie-dense snacks with nutrient-dense alternatives — swap a muffin for Greek yogurt with berries. Stay active with walking, swimming, or prenatal yoga (aim for 150 minutes of moderate activity per week, per ACOG guidelines). Watch liquid calories from juices, smoothies, and sweetened drinks. And talk to your provider about a referral to a registered dietitian.
Gaining Less Than Recommended
Insufficient weight gain raises the risk of preterm birth and low birth weight. The 2025 BMJ study confirmed that below-range gain was associated with increased risks for both of these outcomes.
If you're under target, try eating more frequently — five to six smaller meals instead of three large ones. Add calorie-dense, nutritious foods like avocado, nuts, olive oil, and nut butter. If nausea is the problem, eat bland, starchy foods in small amounts throughout the day. Always discuss persistent low gain with your healthcare provider to rule out underlying causes.
Calorie Needs by Trimester
A common misconception is that pregnancy means "eating for two." In reality, the extra calorie needs are much more modest than that phrase suggests.
| Trimester | Extra Calories Needed | Total Daily (Approx.) |
|---|---|---|
| First (Weeks 1–12) | 0 extra | ~2,000 cal |
| Second (Weeks 13–26) | +340 cal/day | ~2,340 cal |
| Third (Weeks 27–40) | +450 cal/day | ~2,450 cal |
Those extra 340 calories in the second trimester are roughly equivalent to a cup of yogurt with a handful of granola, or a banana with two tablespoons of peanut butter. It's not a lot. The quality of those calories matters just as much as the quantity — prioritize protein, whole grains, fruits, vegetables, and healthy fats.
If you want to dial in your daily calorie needs more precisely based on your age, height, weight, and activity level, try our Calorie Calculator and add the trimester-specific amounts above.
Special Situations: Twins, Underweight, and Obesity
Twin Pregnancies
If you're carrying twins, the recommended weight gain is substantially higher:
- Normal weight: 37–54 lbs
- Overweight: 31–50 lbs
- Obese: 25–42 lbs
Twin pregnancies typically involve faster weight gain beginning in the first trimester, and many providers recommend an additional 300 calories per day on top of the standard singleton recommendations (so roughly 600 extra calories total in the third trimester).
Underweight Women (BMI Below 18.5)
If you were underweight before pregnancy, your target of 28–40 pounds is the highest range. This is because your body needs to build both baby-related tissue and replenish its own nutritional reserves. Your provider may monitor you more closely and recommend calorie-dense foods and possibly a prenatal nutritional supplement beyond the standard prenatal vitamin.
Obese Women (BMI 30+)
The IOM recommends 11–20 pounds for obese women, which is the lowest range. Some research has explored whether even more modest gains (or maintenance of pre-pregnancy weight) might be appropriate for women with a BMI above 35 or 40, but the current evidence doesn't support recommending weight loss during pregnancy. The focus should be on nutrient-rich food choices and regular physical activity, with close monitoring by your healthcare team.
Frequently Asked Questions
Is it normal to lose weight in the first trimester?
Yes, losing a few pounds in the first trimester is common, especially if you have morning sickness. Most women make up for it in the second trimester. However, if you lose more than 5% of your body weight or can't keep any fluids down, contact your healthcare provider — you may need treatment for hyperemesis gravidarum.
How often should I weigh myself during pregnancy?
Most healthcare providers check your weight at each prenatal visit (typically monthly in the first and second trimesters, then every two weeks, then weekly near the end). Weighing yourself at home once a week — same time of day, same conditions — can help you stay on track without becoming obsessive. Daily weigh-ins aren't recommended because normal fluid fluctuations of 2–4 pounds can cause unnecessary anxiety.
What if I was already dieting when I got pregnant?
Stop any calorie-restricted diet as soon as you know you're pregnant. Pregnancy is not the time to lose weight. Even if your BMI is in the obese range, the current guidelines recommend gaining at least 11 pounds. Talk to your provider about transitioning from a weight-loss mindset to a healthy-pregnancy-gain mindset.
Does pregnancy weight gain affect the baby's future health?
Research suggests that excessive gestational weight gain is associated with higher childhood obesity risk in the offspring. A 2024 study in The American Journal of Clinical Nutrition found that both excessive and insufficient gain were linked to adverse outcomes, reinforcing the importance of staying within the recommended ranges.
When do you start losing weight after delivery?
Most women lose 10–13 pounds immediately after delivery (baby, placenta, amniotic fluid, and some water weight). Over the next six weeks, you'll typically lose another 5–10 pounds as your uterus shrinks and excess fluid is excreted. The remaining weight — primarily fat stores — comes off gradually over 6–12 months, especially if you're breastfeeding (which burns an additional 400–500 calories per day).
I'm gaining weight but eating healthy — is something wrong?
Not necessarily. Weight gain during pregnancy is driven by physiological changes (blood volume, fluid, breast tissue, uterine growth) as much as by diet. If you're eating nutrient-dense foods, staying active, and gaining within or near your target range, you're doing great. Rapid or sudden weight gain (more than 2–3 pounds in a single week) should be reported to your provider, as it can sometimes signal preeclampsia or fluid retention issues.
The Bottom Line
Pregnancy weight gain isn't something to fear or obsess over — it's a natural, necessary part of growing a healthy baby. The key is knowing your target range based on your pre-pregnancy BMI, understanding that gain follows a predictable pattern (minimal in the first trimester, steady in the second and third), and focusing on the quality of what you eat rather than just the quantity.
Use the IOM guidelines in this article as your roadmap, track your weight at regular intervals, and work with your healthcare provider to adjust if you're consistently above or below the recommended range. Calculate your due date to map out your timeline, check your BMI to find your target range, and estimate your daily calorie needs with our Calorie Calculator.
Every pregnancy is different. The numbers in this guide are evidence-based starting points — not rigid rules. Trust the process, trust your body, and trust the team of professionals supporting you through this remarkable experience.