How many days after ovulation can you start your period on a 28 day cycle? and can methylpredisnone affect a menstrual cycle?

Ovulation: Will always be close to 14 days before the next period, but it may be a ligule earlier or even later. A glucocorticoid could theoretically disrupt menstrual cycle, bit unless it's very high doses for a prolonged time it is not likely

Usually 14 days: There is almost always a 12-14 day interval between ovulation and menstruation. Rarely women can ovulate twice, sometimes not at the same time, and the period can come a little later (14 days after the 2nd ovulation). Yes, steroids like Prednisone can affect the menstrual cycle. They can delay ovulation or suppress it all together. They can cause irregular bleeding.