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Pregnancy Iron Needs Calculator

Find how much iron you need each day while pregnant.

How it is calculated

The tool uses one fixed daily target of 27 mg of iron for pregnancy and subtracts your average dietary intake: supplement = 27 − dietary iron, never below zero. Both numbers are in milligrams per day, and results are rounded to whole milligrams. Dietary iron must be between 0 and 100, otherwise no result appears. The same 27 mg target applies for the whole pregnancy, because the tool has no trimester input, so it does not raise or lower the figure as pregnancy progresses. It also treats all iron as equal: it does not adjust for how well your body absorbs iron from plant or animal foods. The 27 mg figure is the one this tool applies; other countries set other values.

Worked example

You estimate that your food gives you about 12 mg of iron a day. Daily target = 27 mg. Supplement = 27 − 12 = 15 mg. Result: 15 mg of supplemental iron per day to reach the 27 mg target. If your diet gave 30 mg, the difference would be negative and the tool would show 0 mg.

Try this example →

Common mistakes

  • Adding the iron in a prenatal vitamin to the dietary field. That field is for food only; subtract the vitamin's iron from the result afterwards.
  • Entering iron in micrograms or in grams. The field expects milligrams per day.
  • Expecting the target to change with the trimester. The tool applies the same 27 mg all through pregnancy, so it is not a trimester-specific plan.
  • Taking the supplement figure as a dose to start without advice. Whether to take iron, and how much, depends on blood tests and a clinician's guidance.
  • Using the iron content from a food label without allowing for how much you actually eat. Multiply by your real portions before adding up a day's total.

Sources

About this calculator

Iron requirements roughly double during pregnancy because the body needs to expand maternal blood volume by up to 50%, supply the growing fetus and placenta, and build iron reserves for delivery blood loss — needs that rise sharply through the second and third trimesters as blood volume expansion accelerates. Dietary intake alone often falls short of the increased requirement, which is why iron-deficiency anemia is one of the most common nutritional deficiencies flagged in prenatal bloodwork.

Obstetricians and midwives use iron targets to decide when dietary iron is sufficient versus when a supplement is needed, and to set a supplemental dose that closes the specific gap between what a diet provides and what pregnancy actually requires at that stage — routine prenatal iron supplementation is standard practice in most guidelines specifically because deficiency is so common and consequential for both parent and baby.

This calculator takes your typical dietary iron intake in mg per day and compares it with a fixed pregnancy target of 27 mg per day, the same for every trimester. It returns that daily target along with the supplemental iron needed to close the gap, which is zero if your diet already meets it.

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