How to Calculate Mikvah Night: A Mikvah Calendar Guide

6 min read · October 22, 2026

Also in:עבריתייִדישFrançais

Mikvah night — leil tevilah — is the night after the seventh clean day. To find it you need three things: when the period began, when the hefsek was made, and the seven days after it.

From onset to mikvah night

• Onset: the day the period began is day one.
• Hefsek: on day 5 (Ashkenazi) or day 4 (Sefardi) at the earliest, before sunset.
• Seven clean days: from the morning after the hefsek.
• Mikvah night: the night after the seventh day, after tzeis (nightfall).

So the earliest mikvah night in the Ashkenazi custom is the night after day 12 from the onset: a period that began on a Sunday gives a hefsek on Thursday and mikvah on the Thursday night of the following week.

Tzeis — when the night begins

The tevilah is after nightfall, not at sunset. Calendars use a fixed number of minutes after sunset for tzeis; your mikvah and your rav will tell you which to use where you live.

Shabbos and Yom Tov

Mikvah night on Friday night or on Yom Tov is possible, but preparation must be done before and there are specific halachos; speak to your mikvah in advance.

Nights a tevilah cannot take place

On Yom Kippur and Tisha B'Av there is no tevilah. When mikvah night falls on one of them, when to go instead is a question for your rav — a calendar should mark it, not move it.

After a birth

After a birth the earliest mikvah night is later: after day 14 for a boy and day 21 for a girl in the common reckoning, and only after the seven clean days.

This guide explains the general rules and the common customs. Where poskim differ it says so — it does not rule. For your own questions, ask your rav.