On the website Some Notes on Medieval English Genealogy, Chris Phillips has posted a Julian calender, used in England from the 11th - 16th centuries, and it is organized either by historical year or by regnal year.
From the website:
- This calendar is based on the modern (historical) year, which begins on 1 January. It should be remembered that in medieval times the year was more commonly reckoned from 25 March (or sometimes from 25 December).
- The regnal dates used are those given in the Guide to the Contents of the Public Record Office, vol.1 (1963). Various anomalies concerning regnal years are noted on the tables themselves. In particular alternative versions for William I, based on the dates of accession and coronation, are provided, as the scarcity of early Norman documents dated by regnal year makes it uncertain which convention was used. King John's regnal years were reckoned from his coronation, which took place on Ascension Day, a moveable feast, so that the dates varied from year to year.
- The moveable feast of Easter can, in principle, fall twice in the same regnal year. In practice, this seems to have happened only in 11 Henry VIII during the period covered.