A woman anticipates her menses on certain days based on her previous menstrual pattern. These may include
- yom hachodesh (the day of the month)
- the haflagah (the interval between periods)
- onah beinonit (the thirtieth day)
- veset kavua (a regular period established over at least three cycles)
- veset haguf (specific physical symptoms)
This section deals with the rules for calculating days of anticipated menses (called vesatot, or onot perishah).