The number of days in your cycle is calculated by counting the number of days from the beginning of one period to the beginning of the next period. If you have a short cycle, for example 21 days, and you bleed for 7 days, then you could ovulate right after your period.he number of days in your cycle is calculated by counting the number of days from the beginning of one period to the beginning of the next period. If you have a short cycle, for example 21 days, and you bleed for 7 days, then you could ovulate right after your period.