During the third trimester, you need roughly 450 extra calories per day beyond what you ate before pregnancy. That’s more than the first trimester (when most people don’t need any extra calories at all) and a step up from the second trimester’s 340 extra calories. For context, 450 calories looks like a Greek yogurt parfait with berries and granola plus a couple of rice cakes with almond butter. It’s meaningful but not dramatic.
Why the Number Jumps in Late Pregnancy
Your body’s resting energy burn rises steadily throughout pregnancy, and by the third trimester it’s working considerably harder than baseline. The bulk of pregnancy’s total energy cost comes from this elevated metabolic rate rather than from physical activity. Your heart pumps more blood, your body maintains a larger blood volume, and your baby is gaining weight rapidly, putting on about half a pound per week in the final months.
Research shows that roughly 60% of the increase in metabolic rate during late pregnancy can be explained by the combination of your own weight gain and fetal weight. Hormonal shifts, particularly a rise in growth factors and thyroid hormones, also play a role. Insulin sensitivity drops in the third trimester too, which means your body handles blood sugar differently and benefits from steady, nutrient-dense eating rather than large spikes of simple carbohydrates.
How the Number Changes by Trimester
The 450-calorie figure applies specifically to the third trimester of a singleton pregnancy. Here’s how it breaks down across all three stages:
- First trimester: No extra calories needed for most people
- Second trimester: About 340 extra calories per day
- Third trimester: About 450 extra calories per day
For a person who ate around 2,000 calories before pregnancy, that brings the third-trimester total to roughly 2,400 calories per day. Some older guidelines simplify this to “300 extra calories throughout pregnancy,” but the trimester-specific numbers better reflect how your body’s needs actually change over time.
Twins and Triplets Need More
If you’re carrying multiples, the math scales up. Brigham and Women’s Hospital recommends adding 452 extra calories per baby in the third trimester. For twins, that’s about 900 extra calories a day. For triplets, around 1,350. The second trimester figure for multiples is 340 per baby, and the first trimester is 300 per baby. These are significantly higher than singleton targets, and your provider will likely monitor your weight gain more closely.
What 450 Extra Calories Looks Like
You don’t need to overhaul your diet. The goal is adding one or two nutrient-dense snacks to your existing meals. Some combinations that land close to 450 calories:
- Greek yogurt parfait plus almonds: Half a cup of whole-milk Greek yogurt with berries and granola (about 225 calories) plus an ounce of almonds (167 calories) gets you to roughly 390 calories.
- Rice cakes with almond butter plus a smoothie: Two rice cakes with almond butter (242 calories) plus a hard-boiled egg (78 calories) and some carrots with hummus (176 calories) overshoots slightly but covers protein and fiber well.
- Cottage cheese and fruit plus popcorn: A cup of cottage cheese with berries (198 calories) and three cups of air-popped popcorn (100 calories) with a banana rounds out to about 400 calories.
Protein matters more than raw calorie count. The recommended target during pregnancy is 71 grams of protein per day, and the third trimester is when your baby is building the most tissue. Dairy, eggs, nuts, beans, and lean meats are efficient ways to hit both your calorie and protein goals without relying on empty carbohydrates.
Weight Gain Targets in the Third Trimester
Those 450 extra calories should translate to steady, predictable weight gain. If you started pregnancy at a healthy weight, the guideline is about one pound per week through the second and third trimesters. If you started at a higher weight, the target drops to about half a pound per week. These recommendations come from 2009 guidelines issued by the Institute of Medicine, which remain the current standard. No updated targets have replaced them.
The total weight gain targets by pre-pregnancy BMI look like this:
- Underweight (BMI under 18.5): 28 to 40 pounds total
- Normal weight (BMI 18.5 to 24.9): 25 to 35 pounds total
- Overweight (BMI 25 to 29.9): 15 to 25 pounds total
- Obese (BMI 30 or above): 11 to 20 pounds total
Risks of Eating Too Much or Too Little
Consistently exceeding your calorie needs in the third trimester raises the risk of your baby growing larger than expected, a condition that increases the likelihood of cesarean delivery and birth complications. For people who develop gestational diabetes, gaining above the recommended range nearly doubles the odds of having a larger-than-expected baby. Excess weight gain also correlates with higher insulin requirements and can set up both mother and child for metabolic problems after delivery.
Undereating carries its own risks. Too few calories can slow fetal growth, leave you exhausted, and deprive your body of the nutrients it needs to sustain the increased blood volume and metabolic demands of late pregnancy. The goal is steady, moderate gain, not restriction and not overcompensation.
If you’re already eating well-balanced meals and gaining weight at a steady pace, the 450-calorie addition is often as simple as one extra substantial snack. Track your weight trend rather than obsessing over daily calories. A consistent upward slope within the recommended range is more informative than any single day’s intake.