Start taking folic acid at least one month before you plan to conceive. That’s the minimum recommended by the CDC, and it applies to anyone who could become pregnant. The standard daily dose is 400 micrograms (mcg), found in most prenatal vitamins and many multivitamins. Some women at higher risk need more, and starting earlier gives your body a better buffer.
Why One Month Is the Minimum
The neural tube, the structure that becomes your baby’s brain and spinal cord, forms and closes extremely early. It finishes closing by about 28 days after fertilization, which is roughly six weeks of gestational age. Most people don’t even know they’re pregnant at that point. If your folate levels are low during that narrow window, the risk of neural tube defects like spina bifida rises significantly.
Taking folic acid for at least a month before conception builds up adequate folate stores so they’re already in place when those critical first weeks of development begin. This is why health agencies recommend that all women of reproductive age take 400 mcg daily, even if pregnancy isn’t actively planned. About half of pregnancies are unplanned, and waiting until a positive test often means the neural tube has already closed.
Two to Three Months Is Better
One month is the floor, not the ideal. Many health organizations and fertility specialists recommend starting two to three months before trying to conceive. This longer lead time allows your body to fully replenish its folate stores, especially if your diet has been low in leafy greens and fortified grains, or if factors like smoking, alcohol use, or certain medications have depleted your reserves.
Women at higher risk of neural tube defects are specifically advised to begin supplementation two months before conception at a higher dose of 5,000 mcg (5 mg) per day. This higher-risk group includes women who have had a previous pregnancy affected by a neural tube defect, those with diabetes, obesity with a BMI over 35, malabsorption conditions like inflammatory bowel disease, or those taking antiepileptic drugs or other folate-blocking medications like methotrexate. If any of these apply to you, the earlier start and higher dose can reduce the risk of recurrence by more than 70 percent.
How Long to Continue During Pregnancy
The most critical period is the month before conception through the end of the first trimester (12 weeks of pregnancy). After that, the neural tube has long since closed, so the primary protective window has passed.
That said, folate continues to play a role throughout pregnancy. A randomized trial published in the American Journal of Clinical Nutrition found that women who continued taking 400 mcg of folic acid through the second and third trimesters maintained higher folate levels in their blood and in cord blood at delivery. They also avoided a rise in homocysteine, a marker linked to pregnancy complications, that typically occurs in late pregnancy. Most prenatal vitamins contain folic acid for this reason, and continuing your prenatal through the entire pregnancy is standard practice.
Food Sources Aren’t Enough on Their Own
Natural folate exists in many foods, but it’s fragile. Cooking destroys up to 90 percent of the folate in vegetables. Even raw, food-based folate has low and incomplete bioavailability compared to the synthetic form in supplements. Getting 400 mcg purely from diet is difficult for most people.
That said, folate-rich foods are still worth prioritizing as a complement to supplementation. Some of the best sources per serving:
- Beef liver (3 oz): 215 mcg
- Boiled spinach (½ cup): 131 mcg
- Black-eyed peas (½ cup): 105 mcg
- Fortified breakfast cereal (1 serving): 100 mcg
- Asparagus (4 spears): 89 mcg
- Brussels sprouts (½ cup): 78 mcg
- Avocado (½ cup): 59 mcg
- Broccoli (½ cup): 52 mcg
Enriched grains like white bread, pasta, and rice also contribute meaningful amounts because folic acid is added during processing in the United States and many other countries.
Folic Acid vs. Methylfolate
Your body can’t use folic acid directly. It has to convert it through several enzymatic steps into its active form, called methylfolate, before it does anything useful. This conversion happens slowly and varies quite a bit from person to person. One study found that 86 percent of folic acid reaching the liver was still in its unconverted form, while nearly all natural folate had been properly converted.
This has led to growing interest in methylfolate supplements, which skip the conversion process entirely. Methylfolate is absorbed and used directly, and research shows it raises blood folate levels more quickly and consistently than standard folic acid. However, the CDC still recommends folic acid specifically, because it is the only form with strong evidence from large trials demonstrating neural tube defect prevention. If you’re considering methylfolate, the key point is that 400 mcg daily of either form will raise your blood folate levels to a protective range.
What About MTHFR Gene Variants
You may have seen claims that people with MTHFR gene variants can’t process folic acid and need methylfolate instead. The CDC has addressed this directly: people with MTHFR variants can process all types of folate, including folic acid. Those with the most common variant (MTHFR 677 TT) have blood folate levels only about 16 percent lower than people without the variant when taking the same dose. Taking 400 mcg of folic acid daily raises blood folate levels regardless of MTHFR status, and the CDC states that your folic acid intake matters more than your genotype for determining how much folate ends up in your blood.
In short, an MTHFR variant is not a reason to avoid folic acid or to assume standard supplementation won’t work for you.
A Practical Timeline
If you’re actively planning a pregnancy, start taking 400 mcg of folic acid daily at least one month before you begin trying, ideally two to three months. If you fall into a higher-risk category, talk to your provider about starting 5,000 mcg daily two months before conception and continuing through the first trimester. For everyone else, continue your prenatal vitamin containing folic acid throughout pregnancy. The supplement is inexpensive, widely available, and one of the most effective single interventions for preventing a serious birth defect.