Folic acid for pregnancy: how much, when and why

Folic acid pregnancy guidance is one of the few areas where the US and UK give the same daily figure. Where they differ is how early to start, and who should take more. This page sets out both, each in the source's own terms.

Why folic acid in pregnancy matters

Folic acid is a type of folate, vitamin B9, that helps the body make new cells. The CDC says it is especially important in early pregnancy because it helps the neural tube, which becomes the brain and spine, develop (CDC, "About Folic Acid", 2026).

Neural tube defects are major birth defects of the brain and spine. The CDC names anencephaly, a defect of the brain, and spina bifida, a defect of the spine (CDC, 2026). The US Preventive Services Task Force explains that they happen when the neural tube fails to close, and lists anencephaly, encephalocele and spina bifida as the most common forms (USPSTF, "Folic Acid Supplementation to Prevent Neural Tube Defects", 2023). The NHS adds that folic acid can also help prevent other problems, such as cleft lip and palate and some heart conditions (NHS, "Vitamins, supplements and nutrition in pregnancy", 2026).

Why is folic acid important during pregnancy rather than later? Timing. The CDC says neural tube defects happen in the first few weeks of pregnancy, often before a person knows they are pregnant, so by the time a pregnancy is confirmed it may be too late to prevent one (CDC, 2026). The Task Force says the neural plate usually closes 26 to 28 days after fertilization, so the critical period for folic acid begins at least a month before conception (USPSTF, 2023). The weeks this covers are set out on 4 weeks pregnant and the pages after it.

The evidence is strong. The CDC describes two large randomized trials in the 1990s, one in women who had already had a pregnancy affected by a neural tube defect and one in women who had not, and says both showed that folic acid before and during early pregnancy lowered the chance of an affected baby (CDC, 2026). The Task Force reaffirmed its recommendation in 2023 with grade A, its highest, and reports that folic acid at usual doses is not associated with serious harms (USPSTF, 2023).

How much folic acid for pregnancy: US and UK

The CDC says the US Public Health Service recommends 400 mcg a day for anyone who could become pregnant (CDC, 2026). The Task Force recommends a daily supplement containing 0.4 to 0.8 mg, and notes that this is the generally available dose; it also reports that ACOG, the American Academy of Family Physicians and the American Academy of Pediatrics all recommend 400 micrograms a day for people at average risk (USPSTF, 2023). The NHS recommends 400 micrograms of folic acid every day (NHS, "Vitamins, supplements and nutrition in pregnancy", 2026). The NHS notes that microgram is sometimes written mcg or µg, so labels can look different while saying the same thing.

Folic acid tablets for pregnancy come on their own or as part of a multivitamin. The NHS says folic acid usually comes as tablets or a liquid, and that there are also tablets and capsules that combine it with other vitamins and minerals (NHS, "Folic acid", 2026). If you take a prenatal vitamin, its label shows how much folic acid it contains. The NHS advises checking with a doctor or pharmacist before taking a multivitamin that contains folic acid in pregnancy, and warns that taking too many multivitamin tablets can be dangerous (NHS, "Folic acid", 2026). People searching for the best folic acid for pregnancy will find that the guidance names a dose, not a brand: a plain supplement with 400 micrograms is what it describes. What else a prenatal supplement may hold, and where US and UK advice differs, is in the guide to prenatal vitamins.

When to start taking folic acid, and when to stop

This is where folic acid before pregnancy advice divides by country:

• CDC: start at least 1 month before conception and continue during pregnancy (CDC, 2026).
• USPSTF: start at least 1 month before conception and continue through the first 2 to 3 months of pregnancy (USPSTF, 2023).
• NHS: start when you are trying to get pregnant, ideally 3 months before, or as soon as you find out you are pregnant, and take it for the first 12 weeks (NHS, "Vitamins, supplements and nutrition in pregnancy", 2026).

The amount is the same; the UK advises starting earlier. For anyone taking folic acid when trying to conceive, both countries' advice is already met by starting three months ahead. The Task Force points out that nearly half of US pregnancies are unplanned, which is why it advises folic acid for everyone who could become pregnant rather than only those planning (USPSTF, 2023). The CDC makes the same point: it recommends 400 mcg every day even for people who are not planning a pregnancy (CDC, 2026).

Why stop folic acid at 12 weeks?

Because the neural tube has closed long before then. The Task Force puts closure at 26 to 28 days after fertilization (USPSTF, 2023), and the NHS advises folic acid for the first 12 weeks of pregnancy. Carrying on past 12 weeks is not a problem: the NHS says that taking it for longer than this will not harm your baby (NHS, "Vitamins, supplements and nutrition in pregnancy", 2026). The US sources describe continuing it through the first 2 to 3 months, or during pregnancy, so the two countries' end points are close. The other milestones of these weeks are in the guide to the first trimester.

Who is advised a higher dose

A higher dose is a clinical decision, and the US and UK name different groups and different amounts.

• UK: the NHS recommends a higher dose for anyone planning a pregnancy or less than 12 weeks pregnant if they or the baby's father has a neural tube defect or a relative with one, if they have had a previous pregnancy affected by a neural tube defect, if they have diabetes, if they have a blood condition such as sickle cell anemia or thalassemia, or if they take medicine for epilepsy or HIV. The higher dose is 5 milligrams, which can be prescribed by a GP (NHS, "Vitamins, supplements and nutrition in pregnancy", 2026).
• US: the CDC says that after a past pregnancy with a neural tube defect, the current recommendation is 4,000 mcg a day, starting 1 month before becoming pregnant again and continuing through the first 3 months, after talking with your doctor first (CDC, 2026). The Task Force lists personal, partner or family history of neural tube defects, malabsorption after bariatric surgery, certain antiseizure medicines and genetic changes in folate-related enzymes as factors that call for a conversation with a health professional (USPSTF, 2023).

Which dose applies to a given person is a question for their doctor or midwife. The NHS medicines page also lists medicines that may not mix well with folic acid tablets, including some epilepsy medicines, and advises checking with a doctor or pharmacist (NHS, "Folic acid", 2026). That conversation is part of a preconception checkup.

Folate and folic acid

Folate vs folic acid is a common question, especially when comparing prenatal labels. The CDC says folate is the general name for all forms of vitamin B9, including the food folates in leafy greens and beans and several manufactured forms, and that folic acid is the form used in supplements and fortified foods. It says folic acid is the only type of folate shown to help prevent neural tube defects (CDC, 2026). So, is folate or folic acid better for pregnancy? On the evidence the CDC describes, folic acid is the form shown to work, and it is the form every recommendation on this page names. The Task Force says more research is needed on how genetic variants such as MTHFR affect folate metabolism and supplementation strategies (USPSTF, 2023); it does not recommend a different form.

Folic acid foods for pregnancy

The CDC suggests adding folate-rich foods such as leafy greens, beans or oranges, and checking labels on fortified foods (CDC, 2026). In the US, specific enriched cereal grain products have been fortified with folic acid since 1998, and corn masa flour may be voluntarily fortified since 2016. Even so, the Task Force found that people who may become pregnant do not eat enough fortified food to get the full benefit, and recommends a supplement of at least 400 micrograms (USPSTF, 2023). The NHS says it is difficult to get the amount you need from food alone (NHS, "Vitamins, supplements and nutrition in pregnancy", 2026), and its medicines page notes that the amount added to food such as bread or cereals is much lower than in supplements (NHS, "Folic acid", 2026).

Folic acid and getting pregnant

Folic acid is often bought by people trying to conceive, and it is easy to read that as a fertility aid. None of the guidance on this page presents it that way. The CDC, the Task Force and the NHS recommend folic acid to prevent neural tube defects, and they recommend it before conception only because those defects form so early. If you are wondering about folic acid to get pregnant, these sources present it as being for the baby's development, not for conception. The wider steps before pregnancy, including weight, alcohol and medicines, are in the guide to preconception health, and the due date calculator works out the dates once you are pregnant.

This guide is information, not a diagnosis or a recommendation of treatment, and it is no substitute for your own clinician. See the medical disclaimer.