late period: when to expect next one?

If my period was n days late (but I was not pregnant), and my cycle is usually regular and m days long, when is my next period due? Is my cycle now m+n days long, and I should expect it on day m+n after my LMP? Or will it readjust to the old cycle length, so I should expect it on day m after LMP? Or, will it go back to the old cycle, and I should expect it on day m-n after LMP, as if the last period wasn't late?

[Elaine Brown, MD]

Hi!
Why do I think you are a math teacher or something similar?  Unfortunately, algebra is not very useful when it comes to cycles and hormones.  Usually when a period is late (if it is not due to pregnancy) it is due to a failure to ovulate on schedule.  This is common in women and not anything to worry about if it happens occassionally.  All bets are off however as to when the next cycle will be due.  It often comes within 6-8 weeks, but may take longer.

It is possible that if you call your doctor, he/she might prescribe some progesterone to start your period for you.

Also, if you have a natural period, you can begin to calculate your new cycle with the first day of that period being equivalent to the first day of that cycle.  Usually the new cycle is normal.
If not, you may want to call your doctor at that point.

Good luck!
Dr B