Converting the Julian/Gregorian calendars often left me feeling a little bewildered. I could never quite remember the significant dates that enable you to work out which ‘year’ an event took place. I needed something to help me make sense of it all, so I came up with this little poem. I hope it may be of use to you too sometime.

In 1582, we saw the debut
of a new calendar style.
Pope Gregory decreed, and the Catholics agreed
but global belief took a while.

The loss of 10 days, aligned the moon’s phase
with ecclesiastical dates.
Fifteenth followed fourth, October thenceforth
set the diary that now dominates.

In 1752, adoption ensued
of England’s Gregorian reform.
New Year was reversed to January the first, 
and our calendar year was transformed.

OS or NS, I must now confess,
often leave me rather befuddled.
March 1604, could be therefore,
‘05 or ’03 (now I’m puzzled!).

It all depends, beginning or end,
just when in the month the day be.
Post or before, you must not ignore,
Lady Day (25th) this is key.

So let’s work this out, and eradicate doubt
of dates from Julian years.
Below is a table, which I hope will enable
to allay your conversion fears.

“Since the discrepancy between the Julian calendar year and the astronomical seasons kept growing over time in the centuries that followed, more days had to be skipped in countries that switched to the Gregorian calendar in later years.......The UK dropped 11 days when it converted in 1752.”
www.timeanddate.com/calendar/julian-gregorian-switch