Can I calculate onot from ovulation?
2 November, 2016
I have a question about the Onos. My cycles are 28–29 days, usually giving me 3 days of Onos in a row (29–30–31). I know that my period comes 14 days after I ovulate and most of the time I know exactly when that happens. Once in a while my cycle will be 30 days long but because of previous month's shorter cycle I have to still keep the onos on day 29. But if I know my period won't come before day 30, do I have to observe the earlier onos? In other words, the "official" days of onos may not even be a day I'm expecting my period.
Unfortunately, a calculation based on ovulation two weeks previously, which is largely but not 100% reliable, cannot release a woman from observing onot. Even if you expect your period later based on your ovulation calculation, the halachic requirement to observe the prior interval stands.
Based on your description, however, we are not certain why you wind up keeping three days of onot in a row. If you would like to share more complete information about your onot and calculations over the past few cycles and your customs regarding onah beinonit, we would be happy to review it.
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