How long is the female fertility period?

Fertility period: I'm not 100% certain of the question. Female fertility is variable with age but extends mostly to late 30s and maybe early 40s. The 'fertile period' in a female's cycle is usually taken as 4-5 days around mid-cycle (this is scientifically not correct, but a good strategy for timing when ttc at home.).

Variable: The window of conception (woc) is usually cycle days 10-17 but only about 30% of women fit into this range. About 10% of women were in their woc on any day between days 6-21. Indeed about 3% of women are in their woc on the day of expected menses. (http://1.Usa.Gov/nhkswu) these facts suggest why women conceive when they should not be able to. Use BBT or OPK to help time. (http://bit.Ly/mvk3em).

Short: The egg can only be fertilize for 12-24 hrs.