I recently read on Matzav.com an article by Rabbi Dovid Heber discussing the 247 year cycle in the calendar. He mentioned that every 247 years the Hebrew calendar is exactly identical. Now in the article he mentions that every 247 years the Molad is almost identical. It is only a mere 905 chalakim (50 minutes and 16.67 seconds) earlier.

My question is at what point along the 247 year cycles, due to the constant slow change and creeping up in the Molad will the calendar be forced to change?

  • judaism.stackexchange.com/questions/7955/… Commented Sep 21, 2015 at 17:39
  • Related? judaism.stackexchange.com/a/60034/2
    – Isaac Moses
    Commented Sep 21, 2015 at 17:40
  • 1
    I'm not sure I understand the question... Are you asking after how many shifts of 50 minutes = 0.83 hours, will we drift a whole day? The answer is 24/0.83 hours = 29 cycles.
    – Double AA
    Commented Sep 21, 2015 at 17:51
  • @DoubleAA: At what point will the 247 year cycles not be the same anymore. Commented Sep 21, 2015 at 17:58
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    @GershonGold I still don't understand what's unclear to yuou. Every cycle it drifts 50 minutes. Is that the answer you want? What about what do you want to know will be different when?
    – Double AA
    Commented Sep 21, 2015 at 18:01

1 Answer 1


According to the Pri Chodosh, in his notes on the calendar (in the back of the Shulchan Aruch on Orach Chaim siman 428), the next time there's a difference from 247 years earlier will be in תתמז-תתמח (in machzor שח), which is 2087-2088 on the secular calendar. The last time was in תשז-תשח, which is 1947-1948.

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