Overview
Sof Zman Krias Shema (סוף זמן קריאת שמע), meaning "the end of the time for reciting Shema," is the latest time one may fulfill the Torah obligation of reciting the morning Shema. This deadline is calculated as the end of the third halachic hour of the day.
The Torah commands us to recite Shema "when you lie down and when you rise" (Devarim 6:7). The Sages understood "when you rise" to mean during the time when people typically wake up — the first quarter of the day.
Talmudic Source
The Mishnah Berachos 1:2 states:
"Until when may one recite the morning Shema? Until the end of the third hour, for such is the way of kings to rise at the third hour."
The reasoning is that even kings, who rise late, wake by the third hour. Since Shema must be recited "when you rise," it must be said during the time frame when people wake up.
The Two Main Calculations
The critical question is: what defines a "halachic hour"?
A sha'ah zmanis (halachic hour) is not a fixed 60 minutes, but rather 1/12th of the daylight period. The dispute is how to define that period:
Vilna Gaon (Gra)
The Vilna Gaon (Rabbi Eliyahu of Vilna, 1720-1797) holds that sha'os zmaniyos are calculated from sunrise to sunset.
- The day for mitzvah performance is properly from sunrise to sunset
- Three sha'os zmaniyos = 3/12 = 1/4 of the time from sunrise to sunset
Magen Avraham (M"A)
The Magen Avraham (Rabbi Avraham Gombiner, c. 1635-1682) holds that sha'os zmaniyos are calculated from alos hashachar (dawn) to tzeis hakochavim (nightfall).
- Since "daytime activities" are permitted from dawn until nightfall, the halachic day begins at alos
- Three sha'os zmaniyos = 3/12 = 1/4 of the time from alos to tzeis
Practical Difference
The Magen Avraham's calculation always produces an earlier time than the Gra's for morning zmanim:
| Season | Gra Time | M"A Time | Difference |
|---|---|---|---|
| Winter | Later | Earlier | ~20-30 min |
| Summer | Later | Earlier | ~30-45 min |
| Equinox | Later | Earlier | ~18 min |
Near New York, for example, a sha'ah zmanis based on the Gra lasts approximately:
- 45 minutes near the winter solstice
- 60 minutes near the equinoxes
- 75 minutes near the summer solstice
Common Practice
The prevalent custom among most communities is:
- Be stringent (lechatchila) to recite Shema before the Magen Avraham's deadline
- At minimum, ensure Shema is recited before the Gra's deadline
- If the M"A time passed, one should immediately recite Shema before the Gra's time
The Shulchan Aruch (OC 58:1) establishes that Shema must be recited by the end of the third hour. Later poskim recommend following the M"A calculation lechatchila.
Missing the Zman
- If one missed Sof Zman Shema but it's before chatzos (midday), they should still recite Shema with its blessings
- After chatzos, one recites Shema without the blessings
- The mitzvah of Shema still applies after the zman, but without the full reward of reading it "in its proper time"
About the Magen Avraham
Rabbi Avraham Abele Gombiner (c. 1635-1682) was born in Gąbin (Gombin), Poland. After his parents were killed in 1655 during the aftermath of the Chmielnicki massacres, he moved to Leszno and later to Kalisz, where he became Rosh Yeshiva.
His commentary Magen Avraham on the Shulchan Aruch's Orach Chaim became one of the most influential halachic works, though its terse style required explanation by later commentators.
About the Vilna Gaon
Rabbi Eliyahu ben Shlomo Zalman (1720-1797), known as the Vilna Gaon or the Gra, was the foremost leader of non-Hasidic Jewry. He was a prodigious scholar in Talmud, Kabbalah, and even secular sciences including mathematics and astronomy — knowledge he considered essential for understanding Torah.
His rulings on zmanim reflect his astronomical expertise and his view that halachic times should correspond to observable natural phenomena.