Reference Centre, Calendars-Calculators
Regnal Year Calculator
This page will take a date in regnal years and return an ordinary date. For instance, if you enter 6/1 1 Elizabeth I, you will get the year 1559 because June 1st in her first regnal year occurred in 1559.
*Dual years written as "1324/5" reflect Old Style dating and will only occur between January 1 and March 24 in each year up to and including 1752, when the Gregorian calendar was adopted by England, Wales and most of her colonies and territories. Prior to 1753, the Julian calendar was in use and the legal year had begun on March 25. For example, January 1 in Elizabeth I's 1st regnal year occurred in the Christian year 1559, but legally the year was still 1558, and would be until March 25. From January 1 to March 24, the convention is to note both years with a slash between them, e.g. "1558/9."
Keep in mind that a monarch's last regnal year is cut short by death or deposition and may not include all dates.
Remember also that from 1582 onward, English dates (Old Style) will not correspond with Continental dates.