Eating for Two Is About Three Hundred Calories — and Almost None of Them in the First Trimester

The requirement is a schedule, not a number

The phrase "eating for two" implies a doubling. The published figures say something closer to a rounding error, at least at the start. EFSA's Dietary Reference Values put the extra average requirement at 0.29 megajoules a day in the first trimester, 1.1 in the second and 2.1 in the third. Megajoules are how European reference values are published; at EFSA's own conversion of 1 MJ = 238.83 kcal, those are 69, 263 and 502 kilocalories, which EFSA rounds to 70, 260 and 500. Everything below is in kilocalories, because that is what food labels use in all six of our markets, but the underlying documents are in MJ and the two are the same quantity.

Put those against a plausible baseline and the shape becomes clear. EFSA's own average requirement for a moderately active woman aged 18 to 29 is 9.0 MJ a day, or about 2,150 kcal. The trimester increments are therefore +3.2%, +12.2% and +23.3% of what she was already eating. Only the third of those is large enough to notice. And summed over the whole pregnancy — three 91-day trimesters — EFSA's schedule comes to 318 MJ, which is within about 1% of the 321 MJ (77,000 kcal) that FAO/WHO/UNU derived by a completely different route, from the composition of the tissue laid down during a 12 kg weight gain. Two committees, two methods, the same total. That agreement is the reason to trust the order of magnitude even where the trimester splits differ.

One more way to size it. Divide 77,000 kcal by the same 2,150 kcal baseline and a whole pregnancy costs about 36 extra days of ordinary eating, spread across nine months. That is the honest scale of the thing.

Three authorities, three answers — and one of them asks your starting BMI

EFSA gives 70, 260 and 500. FAO/WHO/UNU gives 85, 285 and 475. The differences are smaller than the day-to-day variation in anyone's eating and there is no reason to prefer one over the other. The interesting disagreement is with the 2023 US reference intakes, which changed the method rather than the numbers. Instead of a flat trimester increment, NASEM's equation predicts total energy expenditure and then adds a separate term for the tissue being deposited — and that term depends on pre-pregnancy BMI: +300 kcal a day if the pregnancy started in the underweight category, +200 for normal weight, +150 for overweight, and −50 for obesity. In the first trimester there is no increment at all; the equation for a non-pregnant woman is used.

The negative term deserves an explanation rather than a raised eyebrow. It is not a recommendation to eat less; it reflects the fact that the recommended weight gain in that group is smaller, so less new tissue has to be built. And it is precisely the point at which a calculator stops being able to help: whether a smaller gain is right for a given pregnancy is a clinical judgement about that pregnancy, made with the person who is measuring it.

What 70, 260 and 500 kcal actually look like

Atwater's general factors — 4 kcal per gram of protein, 9 per gram of fat, 4 per gram of carbohydrate — are what every food label is built on, and they turn the increments into something you can picture. The first-trimester 70 kcal is 7.8 g of fat or 17.5 g of carbohydrate: a spoonful of oil, or a small piece of fruit. The second-trimester 260 kcal is 28.9 g of fat or 65 g of carbohydrate: a pot of yoghurt and a banana, roughly. The third-trimester 500 kcal is 55.6 g of fat or 125 g of carbohydrate: a proper extra snack, not an extra dinner.

This is worth stating plainly because the folk version of the advice does real harm in both directions. Someone who hears "eating for two" and adds a second dinner is adding roughly 700 kcal, which is more than the third-trimester increment and about ten times the first-trimester one. Someone who reads the small number and concludes that pregnancy needs nothing extra has missed that appetite is the regulator here, not arithmetic — and that in the third trimester the requirement is genuinely a quarter higher.

The requirement that rises fastest is not energy

Here is the part that matters more than the calorie count, and it falls straight out of EFSA's own tables. Take a woman of 60 kg. Her protein reference intake is 0.83 g per kilogram, so 49.8 g a day. EFSA adds 1 g in the first trimester, 9 in the second and 28 in the third — taking her to 77.8 g, an increase of 56.2%. Over the same period energy rises 23.3%. Folate goes from 330 to 600 µg of dietary folate equivalents, an increase of 81.8%. Iodine goes from 150 to 200 µg, an increase of 33.3%. Protein climbs about 2.4 times faster than energy; folate about 3.5 times faster.

The consequence is the whole point. Suppose the extra 500 kcal are eaten as more of exactly the same food. Then the nutrient density of the diet is unchanged, and the protein requirement is met only if the original diet was already delivering 56% more protein per calorie than it needed to. Compute it directly: at baseline the diet must supply 23.2 g of protein per 1,000 kcal; in the third trimester it must supply 29.3 g per 1,000 kcal, 26.7% more. Folate has to go from 154 to 226 µg per 1,000 kcal, 47.4% more. Iodine, which rides on a smaller increase, needs only 8.1% more per calorie. So the same plate, scaled up, does not get there for protein or folate. Different food does.

Where the authorities genuinely disagree: iron, iodine, folate

On energy the committees agree within a rounding error. On micronutrients they do not, and the differences are large enough to matter. Iron is the clearest case: EFSA's population reference intake for a premenopausal woman is 16 mg a day, and EFSA leaves it at 16 mg during pregnancy — on the reasoning that menstruation stops and absorption rises. The US reference intake goes the other way, from 18 mg to 27 mg, a 50% increase. The WHO does something different again and recommends supplementation rather than a dietary target: daily oral iron of 30 to 60 mg of elemental iron together with 400 µg of folic acid, as routine antenatal care. Three defensible positions, and the one that applies to you is the one your maternity service follows.

Iodine shows the same pattern more mildly: EFSA raises the adequate intake from 150 to 200 µg a day, the US reference intake goes to 220 µg, and the WHO/UNICEF technical consultation of 2007 recommends 250 µg for pregnancy and for breastfeeding. Folate is the one place everyone lines up — both EFSA and the US set 600 µg of dietary folate equivalents during pregnancy — and it is also the one place where the recommendation is not really about diet at all, because the neural tube closes in the fourth week after conception, before most people know they are pregnant. That is why every guideline puts folic acid before conception rather than during pregnancy.

Why weight gain is banded by starting BMI and food is not

The 2009 Institute of Medicine guidelines set total gestational weight gain by pre-pregnancy BMI: 12.5–18 kg (28–40 lb) if the pregnancy began under a BMI of 18.5; 11.5–16 kg (25–35 lb) from 18.5 to 24.9; 7–11.5 kg (15–25 lb) from 25.0 to 29.9; and 5–9 kg (11–20 lb) at 30 and above. The corresponding rates in the second and third trimesters are 0.51, 0.42, 0.28 and 0.22 kg a week — roughly 1, 1, 0.6 and 0.5 lb — each with its own published range. We have a separate article on those bands and where they came from; the point here is narrower.

It is this. Weight gain is a measurement — something that can be observed, plotted and responded to. Energy intake is not: nobody can measure their own intake to within 200 kcal a day, and even a laboratory needs doubly labelled water to measure expenditure. So the guidelines are banded where the feedback exists and left as a population average where it does not. A pregnancy calorie calculator gives you the population average. The band your clinician watches is the weight, and it is the weight that will tell them whether the average was right for you.

What no calculator on this page can see

Twins change the arithmetic and the guidance; the IOM bands above are for singleton pregnancies and there are separate provisional ranges for twins. Persistent vomiting changes it in the other direction and is a reason to be seen, not to eat more. Gestational diabetes changes the composition of the diet rather than its size, and is managed with a specific team. A pregnancy in adolescence carries the girl's own growth on top of the pregnancy's. A history of bariatric surgery changes absorption of exactly the nutrients discussed above. And appetite itself is a regulator that works, most of the time, better than any equation.

Frequently asked questions

So do I need extra calories in the first trimester or not?

The authorities differ, and the difference is small. EFSA says +70 kcal a day, FAO/WHO/UNU says +85, and the 2023 US reference intakes say no increment at all and use the non-pregnant equation. All three are, in practice, saying the same thing: the first trimester costs almost nothing in energy terms. That is also the trimester in which many people eat less rather than more because of nausea, which is one reason the reference values do not try to be prescriptive here.

Why do European and American figures differ if the biology is the same?

Because reference values are not measurements of a person; they are constructions built on assumptions. The assumed weight gain, the assumed baseline body weight, the assumed activity level, the choice of whether to model deposition separately, and the decision about how much to round all move the answer. EFSA and FAO/WHO/UNU landed within about 1% of each other on the total energy cost of pregnancy precisely because they modelled the same tissue; they differ on the trimester split because they smoothed it differently. The 2023 US report differs more because it rebuilt the method around measured total energy expenditure.

If protein needs rise 56% and energy only 23%, does that mean a high-protein diet?

No. It means the extra energy should not arrive as pure carbohydrate or pure fat. In absolute terms EFSA's third-trimester figure for a 60 kg woman is 77.8 g of protein a day, which most ordinary mixed diets in our six markets already exceed. The arithmetic matters most for people whose diet was marginal on protein to begin with, and for anyone eating to a restricted pattern — which is a conversation with a dietitian, not with a page.

Should I take an iron supplement in pregnancy?

That is a question for your clinician, and the honest answer is that guidance differs by country and by your own blood results. The WHO recommends routine daily supplementation with 30 to 60 mg of elemental iron plus 400 µg of folic acid in antenatal care. Several European services instead test for anaemia and supplement only where indicated, which is consistent with EFSA leaving the reference intake unchanged during pregnancy. Iron is not harmless in excess, and the decision belongs to whoever can see your ferritin and haemoglobin.

Does the calculator's number change if I am carrying twins?

Yes, and by more than a simple doubling would suggest — but no published set of reference values covers multiple pregnancy with the confidence it covers singletons. The IOM issued only provisional gestational weight-gain ranges for twins, and the energy reference values above are explicitly derived for a single fetus. If you are carrying more than one, the numbers on this page are not the ones that apply to you, and your obstetric team will be following a different plan.