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In order to begin counting the seven clean days following her period, a woman must establish that she has indeed stopped bleeding, by conducting a thorough internal check (bedika). This check is known as the hefsek tahara. Even after she has stopped bleeding though, old blood may remain in the vagina. Therefore, before attempting a hefsek, a woman should take a soft cloth and wet it (to avoid hurting the sensitive skin), wrap it around her finger, and clean out any vestiges of blood. Sometimes she may need to repeat this a few times. Afterwards, she should use a small, clean white cloth to do a thorough internal check. If the cloth shows no shade of red or black, she has confirmed her period has ended. It is convenient to use pre-packaged bedika cloths (which can be bought at a mikveh) for both the pre-check cleaning and the checking itself.
According to Jewish law, the day starts with sunset, so the hefsek tahara should ideally be done in the last few hours before sunset (shki’a). It is also preferable to use a mokh daĥuk; this means in addition to the thorough check with the bedika cloth, it is also good to leave a bedika cloth in the vagina during twilight, which extends from sunset until the emergence of stars (tzeit). (These times can be found in some local Jewish calendars as well as on the MyZmanim website.) If a woman was not able to do a hefsek before sunset, she has forfeited the day, and cannot begin her seven-day count until sunset the next day. Therefore, if a woman is worried she will forget to do a hefsek close to sunset, she should do it earlier in the afternoon, or even in the morning.
