1,884 kcal maintenance + 340 kcal pregnancy add-on
| Trimester | Pregnancy add-on | Total / day |
|---|---|---|
| 1st | — | 1,884 kcal |
| 2nd | +340 kcal | 2,224 kcal |
| 3rd | +452 kcal | 2,336 kcal |
Estimate your daily calorie needs during pregnancy. Start from your pre-pregnancy maintenance calories (resting metabolic rate by the Mifflin-St Jeor equation, scaled for activity), then add the Institute of Medicine's recommended energy increase for your trimester.
Daily calories = (Mifflin-St Jeor RMR × activity) + trimester add-on (0 / 340 / 452 kcal)
Pregnancy raises energy needs, but not from the first day and not by a constant amount. The calculator works in two steps. First it estimates your pre-pregnancy maintenance calories: it computes resting metabolic rate (RMR) — the energy your body uses at rest — from your weight, height, and age using the Mifflin-St Jeor equation, a widely used formula that predicts measured RMR more accurately than the older Harris-Benedict formula. That RMR is then multiplied by an activity factor (from 1.2 for sedentary up to 1.9 for very active) to give total daily energy expenditure (TDEE) — your maintenance calories. Second, it adds the extra energy pregnancy requires. The Institute of Medicine's Dietary Reference Intakes recommend no extra calories in the first trimester, about 340 extra calories per day in the second trimester, and about 452 extra per day in the third, reflecting the rising energy cost of the growing baby, placenta, and maternal tissues. The result is an estimate of your total daily calories for the trimester you select. It is a starting point, not a prescription: real needs vary with pre-pregnancy weight, the number of babies, medical conditions, and how much weight you have gained so far, so your prenatal provider's guidance always takes precedence.
A 30-year-old who weighed 60 kg at 165 cm before pregnancy, lightly active, is in her second trimester. How many calories does she need each day?
Two ideas drive the estimate. The first is resting metabolic rate — the calories your body burns just keeping you alive at rest — which scales with body size and falls slightly with age; the Mifflin-St Jeor equation predicts it from weight, height, age, and sex and is preferred over Harris-Benedict for accuracy. The second is the pregnancy energy increment, which is not a flat '+300 calories.' The Institute of Medicine ties it to trimester because the energy cost of pregnancy rises as the pregnancy progresses: roughly zero extra in the first trimester, +340 kcal/day in the second, and +452 kcal/day in the third. These are population averages for a healthy singleton pregnancy starting at a normal pre-pregnancy weight. People carrying twins need more; people who started pregnancy underweight or overweight may be advised to aim higher or lower; and the quality of the calories matters as much as the quantity — protein, iron, folate, calcium, and other nutrients have their own pregnancy targets that a calorie number does not capture. The calorie estimate is best used alongside the recommended weight-gain range for your pre-pregnancy BMI, which is the metric prenatal providers actually track.
According to the Institute of Medicine, you need no extra calories in the first trimester, about 340 extra calories per day in the second trimester, and about 452 extra per day in the third. These are added on top of your pre-pregnancy maintenance calories — they are not a doubling of intake. The popular 'eating for two' phrase overstates the real increase by a wide margin.
It first estimates your resting metabolic rate from your weight, height, and age using the Mifflin-St Jeor equation, multiplies that by an activity factor to get pre-pregnancy maintenance calories (TDEE), and then adds the Institute of Medicine's trimester-specific energy increase (0, 340, or 452 kcal/day). The total is an estimate of your daily calorie needs for the trimester you select.
Mifflin-St Jeor is a widely used equation for estimating resting energy expenditure in healthy adults, and studies have found it predicts measured values more accurately than the older Harris-Benedict equation. It uses weight, height, age, and sex — the same inputs, but with coefficients fit to a larger, more representative sample.
No. A twin (or higher-order) pregnancy requires more energy than a singleton, and the Institute of Medicine's single-baby increments do not apply directly. If you are carrying multiples, use this only as a rough floor and follow the individualized calorie and weight-gain targets your prenatal provider gives you.
For most healthy pregnancies, strict calorie counting is not necessary or recommended — appetite, regular weighing against the recommended gain for your BMI, and the quality of your diet are better guides. The calorie estimate is useful for understanding roughly how much your needs rise, not as a rule to police every meal. Always defer to your provider, especially if you have diabetes, are underweight or overweight, or have other medical conditions.
It can. The trimester calorie increments are population averages for a healthy-weight singleton pregnancy. If you began pregnancy underweight or with obesity, your provider may set a different energy target and a different weight-gain goal. Pair this estimate with the recommended weight-gain range for your pre-pregnancy BMI for a fuller picture.
Reference:
Mifflin MD, St Jeor ST, Hill LA, Scott BJ, Daugherty SA, Koh YO. A new predictive equation for resting energy expenditure in healthy individuals. Am J Clin Nutr. 1990;51(2):241-247. https://doi.org/10.1093/ajcn/51.2.241 · Trimester energy increments (Institute of Medicine Dietary Reference Intakes): Kominiarek MA, Rajan P. Nutrition Recommendations in Pregnancy and Lactation. Med Clin North Am. 2016;100(6):1199-1215. https://pmc.ncbi.nlm.nih.gov/articles/PMC5104202/