If there’s any chance you could become pregnant, the best time to start folic acid is now. Waiting for a positive test can be too late for the part of pregnancy it protects most.

The short version

  • Folic acid: start at least 1 month before you try to get pregnant and keep taking it through the first 2 to 3 months of pregnancy, according to the U.S. Preventive Services Task Force. That’s 400 to 800 mcg a day.
  • Even if you aren’t planning a pregnancy: the CDC recommends 400 mcg of folic acid every day for anyone who could become pregnant, from a vitamin, fortified foods, or both.
  • Prenatal vitamin: ACOG and the Academy of Nutrition and Dietetics recommend that pregnant women take one every day, according to the NIH. Many providers suggest starting when you begin planning.
  • Keep going: take it through your whole pregnancy, then ask your provider what to take after birth.

Why the timing matters

If you have enough folic acid in your body before you get pregnant, your baby’s risk of a neural tube defect (NTD) is greatly reduced. NTDs are major birth defects of the brain and spine, such as anencephaly and spina bifida. Spina bifida can cause problems with movement, bowel and bladder control, and learning.

The problem is when they happen. NTDs form within the first 28 days after conception, which is usually before a woman knows she’s pregnant. As the CDC puts it, by the time you realize you’re pregnant, it might be too late to prevent a neural tube defect. And since about half of all U.S. pregnancies are unplanned, many women never get the chance to start folic acid after deciding to get pregnant.

Folic acid is the man-made form of folate (vitamin B9). It’s in prenatal vitamins and in fortified foods like breakfast cereals, while folate, the natural form, is in fruits, vegetables, and beans.

A timeline

  1. At least 1 month before you try. Start folic acid: 400 to 800 mcg a day, from a vitamin or prenatal.
  2. Days 1 to 28 after conception. The neural tube closes, often before you know you are pregnant.
  3. First 12 weeks. Keep taking folic acid through the first 2 to 3 months.
  4. Rest of pregnancy. Keep taking a daily prenatal vitamin.
  5. After birth. Ask your provider whether to keep your prenatal while breastfeeding.

The timeline follows the Task Force’s advice. Other groups give slightly different start and end points, summarized here by the NIH:

Source Who Start Stop
U.S. Preventive Services Task Force and Dietary Guidelines Anyone planning or able to become pregnant At least 1 month before conception After the first 2 to 3 months of pregnancy
ACOG Anyone planning or able to become pregnant At least 1 month before conception After the first 12 weeks
CDC Anyone who could become pregnant Now, and every day Ongoing
World Health Organization Women planning a pregnancy As early as possible, ideally 2 months before After the first 12 weeks
CDC, after a pregnancy affected by an NTD Planning another pregnancy 1 month before, at 4,000 mcg a day After the first 3 months
ACOG, after an NTD or with a family history of one (you or your partner) Planning a pregnancy 3 months before, at 4,000 mcg a day After the first 12 weeks

What about the rest of your prenatal?

Folic acid is the one nutrient with a firm “start before” deadline, because the neural tube closes so early. The rest of the prenatal vitamin (iron, iodine, choline, vitamin D) matters through pregnancy, and many providers suggest starting it once you begin planning, according to the NIH’s summary of the Dietary Guidelines. For iodine, the American Thyroid Association suggests starting 150 mcg a day ideally 3 months before conception, as the NIH notes. Don’t take a prenatal and a separate multivitamin together without checking with your provider, since the amounts add up.

Common situations

I’m already pregnant and haven’t started. Start now and tell your provider. The neural tube closes in the first month, so you may have missed part of that window, but your folate need stays higher for the whole pregnancy, at 600 mcg DFE a day, according to the NIH. Spina bifida affects about 1 in 2,857 U.S. births, according to the CDC, so most pregnancies aren’t affected.

I’m not trying, but I could get pregnant. Take 400 mcg of folic acid every day, as the CDC recommends. Check your vitamin and food labels for “folic acid.”

I’ve had a pregnancy affected by an NTD, I have a family history of NTDs, or I take seizure medicine. Talk with your doctor before you try to get pregnant. The right amount of folic acid may be higher, and your medicines may need adjusting. The Task Force’s 400 to 800 mcg recommendation doesn’t apply to women who have had an NTD-affected pregnancy or who take medicines that block folic acid. See Why Folic Acid Matters in Pregnancy.

I’m breastfeeding. The CDC’s 400 mcg recommendation still applies if you could become pregnant again. The Dietary Guidelines for Americans suggest asking your provider whether to keep taking your prenatal or switch to another supplement. See Prenatal Vitamins While Breastfeeding.

What to do now

  • If there’s any chance you could become pregnant, check that your vitamin has 400 mcg of folic acid, and take it every day.
  • If you’re planning a pregnancy, start a prenatal vitamin at least a month before you try, and ask your provider about your medicines and about iodine.
  • If you’ve had an NTD-affected pregnancy or take seizure medicine, call your doctor before you try.
  • Eat folate-rich foods like leafy greens, beans, and oranges, and look for “folic acid” on cereal and bread labels.

Related reading

Sources

Updated November 2026. This article is for general information and is not a substitute for advice from your health care provider.