For women, ovulation calculator is very useful to keep on track on their period time each of month. Normal ovulation period is approximately four weeks and in the middle of menstruation period. In this calculator, you just put time when the last period happens then system will calculate for the next one.
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Sometime, period does not do as you expected but this situation is rare unless you have unexpected health problem. Another function of this calculator is prediction of pregnancy for women who just got married or want to add child on family planning. Therefore, you do not have to study rigorous medical field to understand ovulation.