I just realized a mistake “I made
I got the dates from “timeanddate . com”
The times given are Coordinated universal time which is 5 hours ahead of New York time.
Thus for New york the above dates are not accurate
Some chnage to become correct for you
for example last year 2022, equinox was Sep 23 01:03 UTC (which results in incorrect Dec 5th) but in NY this was Sep 22 9:03 PM (which results in correct Dec 4th)
Nonethless my point still stands:
1) Your rule is limited to certian time zones, making it not such a good rule, in London my list above with the 14% error rate is correct.
2) Correcting for time difference makes some of your years more correct (eg 2022 becomes right)
Others become wrong, for example 2039 in London your system works : Equinox will be Sep 23 03:49 UTC which results in Dec 5th according to both your system and the halachic one. but in NY the Equinox will be few hours earlier (local time) Sep 22 11:48 PM which would lead to Dec 4 start date using your system while Dec 5th using the halachic system (though to be fair it is more accurate in NY than in London )
3) If you use it as a cute trick that usually works fine. But this is a-halachic in Halacha when counting days we always (almost?) count the first day as day 1. If you say ignore that and just add 60 it works fine. but to make it sound like this is how the cheshbon works when it is not true makes me squeamish.
4) You say “I am trying to find an easy way of calculating.”
This is the part I really don’t get, it is much easier to check your siddur and see “Start saying Vesein Tal umatar on Dec 4t hat MAariv unless it is before a leap year in whcih case it is Dec 5th” or google “When do we start” seems os much easier than relying on your method although it usually works.
Who is this easy calculation for?
for those who want to understand how Dec 4th was chosen and why this year its Dec 5th give them the correct answer. Who gains from your incorrect sytem (although it usually works)?
5) Your system will fall apart in 2100