To find the last day you must abstain or use contraception with the calendar method, subtract 11 days from your longest cycle. Draw an X through that date also. Remember, you need to chart your cycles for at least eight months before you can calculate your safe times. Be sure to confirm this with other methods. They are also likely from the second X to the next circle.
Unsafe days appear between the two X s.
The first part of any cycle may be irregular. Trying to add a few days of intercourse in the early part of your cycle can be risky when attempting to prevent an unplanned pregnancy. Learning the meaning of changes in your normal vaginal discharge may reduce miscalculations. But always be guided by any sign that says you may be fertile. This site is produced by The Journal of the American Medical Association .