I took one per day, for one copy of a MTHFR mutation.
If you have 2 copies of certain mutations, they may want you to take 2 per day instead of 1 (this was per the Beer Center).
If your homocysteine levels are normal though, you probably are absorbing folic acid just fine, the extra is just for assurance. A very large percentage of the population has one or more MTHFR mutations without ever knowing and having no problems with pregnancies.
There is an OTC Folgard that only has 800 units of folic acid (my pharmacy tried to fill my script with this, not understanding the difference between the OTC and Rx versions). Most prenatal vitamins have 800, some Rx prenatals have 1000, the Folgard 2.2 Rx has 2500 units I believe.
There is some concern that too much folic acid may not be that great either, linked to certain cancers (lung, colon, prostate) if you google "too much folic acid" or similar, I only take the extra during cycling and pregnancy.