Date Converter

What does a Gregorian date look like in the records?

A Gregorian date reads like any modern date: the day, the month and a year that runs from January 1st. It is the calendar in use today, introduced in October 1582 and adopted place by place over the next three and a half centuries: the Catholic states of Italy, Spain, Portugal and Poland at once; France that December; the Catholic German states within two years; the Protestant German states, Denmark and the Dutch provinces still on the old calendar in 1700; Britain and its colonies in September 1752; Sweden in 1753; Russia in 1918; Greece in 1923.

Nothing on the page tells the two calendars apart: a Gregorian date and a Julian one look the same. What decides it is where and when the record was written. A Catholic register kept across the Channel in 1740 is Gregorian; a parish register kept in Kent in the same year is Julian, because England had not yet changed. The adoption date for the place should be confirmed before a date is treated as Gregorian; see the adoption dates by country below.

What does a Julian date look like in the records, and which year does it carry?

The Julian calendar was Europe’s calendar for sixteen centuries and stayed in use, place by place, until each adopted the Gregorian. A Julian date reads exactly like a Gregorian one — the same day and month names — but sits behind it by a gap that grew from ten days in 1582 to thirteen after 1900. A record is Julian when the record-keeper’s country had not yet changed: an English or Welsh record before September 1752, a Scottish one before the same date, a Protestant German or Dutch one before 1700, a Russian one before 1918.

Julian records number the year in one of two ways. Most of the Continent, and Scotland from 1600, began the year on January 1st, so the year reads as it would today. England, Wales, Ireland and the American colonies began the legal year on March 25th until 1752 — Old Style — so a date from January 1st to March 24th runs a year behind the modern count: a burial entered as “10 February 1699” took place in the year now numbered 1700. Record-keepers who knew the difference mattered sometimes wrote both, as “10 February 1699/1700”; the second figure is not a doubt but the year as it is counted now.

Two things to watch. The Julian calendar keeps February 29th in 1700, 1800 and 1900, which the Gregorian does not, so a record dated to one of those days is Julian by that fact alone. And Scotland changed the two things separately — the year in 1600, the calendar in 1752 — so a Scottish February 1700 has a modern year number but Julian days.

Why are the year and the day two separate corrections?

The Gregorian calendar was decreed by the Pope in 1582, and most of Europe already began its year on January 1st. England and Wales adopted both in 1752, under one Act of Parliament: from January 1st the legal year was counted from January 1st instead of March 25th, and in September the calendar changed from Julian to Gregorian, dropping eleven days. Because England made both changes in the same year they are often treated as one, but they correct different things, and not every place adopted both together. The year rule changes only the year number, and only for dates from January 1st to March 24th; the day and month stay as written. The calendar change moves the day itself, by however many days separated the calendars at the time, at any time of year. The converter keeps them apart: “Julian, Mar 25th start” to “Julian, Jan 1st start” corrects the year alone; “Julian, Jan 1st start” to “Gregorian” corrects the day alone; and “Julian, Mar 25th start” to “Gregorian” corrects both. Between them, the three conversions cover a record that used either calendar with a January 1st or March 25th year start.

Which corrections a record needs depends on where and when it was written, and on the time of year. An English record from June 1740 is Julian, so the day needs correcting, but the year does not — June falls after March 25th. A February 1740 record from England needs both: the year, because February fell before the legal new year, and the day, because the calendar was still Julian. A Scottish record from February 1700 needs the day corrected but not the year, since Scotland had moved its new year to January 1st in 1600 while keeping the Julian calendar. A French record from the same February needs neither.

Why are there two calendars with different dates?

The Gregorian calendar is a reform of the Julian, not a replacement: it kept the months, the days and the seven-day week and changed one rule. The Julian calendar, in use since Julius Caesar, made every fourth year a leap year, which assumes a year of exactly 365¼ days. The true year is about eleven minutes shorter, so the Julian calendar gains a day every 128 years.

By the sixteenth century the spring equinox, fixed at March 21st by the Council of Nicaea in 325 for the reckoning of Easter, was falling on March 11th by the calendar. The reform authorized by Pope Gregory XIII in 1582, on the mathematics of Aloysius Lilius and Christopher Clavius, dropped ten days to put the equinox back — Thursday, October 4th was followed by Friday, October 15th, the weekdays running on unbroken — and changed the leap-year rule so the drift would not return.

Why does the day correction change by century?

The Julian calendar makes every fourth year a leap year without exception. The Gregorian skips the century years unless they divide by 400: 1600 and 2000 were leap years in both calendars, but 1700, 1800 and 1900 were leap years in the Julian only, and 2100 will be. At each of those Februaries the gap between the calendars grew by a day: 10 days from 1582, 11 from March 1700, 12 from March 1800, 13 from March 1900, and 14 from March 2100. A Julian date is therefore not converted by adding ten days; the correction depends on when the date falls.

What does Old Style/New Style mean?

Old Style (OS) refers to the way the year was numbered when the legal new year began on March 25th (Lady Day) rather than January 1st. Dates recorded between January 1st and March 24th therefore carried the previous year’s number.

For example, a register kept in England and dated “10 February 1700” was recorded as 1700 under the Old Style system but falls in 1701 under the New Style year.

In a British record the abbreviations O.S. and N.S. can refer to either change or both — the year reckoning, the calendar, or the two together — so the marking alone does not say which correction a date has had. Elsewhere in Europe, where the year had long begun on January 1st, they usually mean the calendar alone.

What is a dual date?

Record-keepers sometimes wrote both year numbers to make the difference clear. A date such as “10 February 1699/1700” means the date was 1699 according to the Old Style legal year but 1700 according to the New Style year.

A dual date is not a range or an uncertain date. It carries both year reckonings. When transcribing a historical record, retaining both numbers preserves information that can otherwise be lost.

What happened when England changed calendars in 1752?

England and Wales adopted the Gregorian calendar in September 1752. Wednesday, September 2, 1752, was followed by Thursday, September 14, 1752. The eleven dates between them were omitted from the calendar.

The change also made January 1st the beginning of the legal year. Before 1752, the English legal year began on March 25th, so dates between January 1st and March 24th can have both an Old Style and a New Style year.

What happened to the eleven days between the last Julian date and the first Gregorian?

They never occurred, so nothing is dated to them. An English record apparently dated September 5, 1752 is either mis-dated or not English.

People alive across the change could have dates recorded differently before and after it. George Washington, for example, was born on February 11, 1731 under the calendar then in use in Virginia. After the 1752 change, his birthday was reckoned as February 22, 1732. The day component belongs to the Julian ↔ Gregorian conversion; the year component reflects the change from the Old Style to the New Style year.

Why did the new year move to January 1st?

It was less a move than a return. January 1st had been the start of the Roman civil year since Julius Caesar’s calendar reform, and the Julian calendar England used had always counted its months from January. March 25th — Lady Day, the feast of the Annunciation — was a medieval church convention adopted for the legal year in England around the twelfth century, and it never displaced January 1st entirely: almanacs and everyday reckoning often ran from January, which is why record-keepers wrote dual dates for the months in between.

Most of Europe had settled on January 1st by the sixteenth century, Scotland in 1600. When England and Wales reformed the calendar in 1752 they took the opportunity to bring the legal year into line with the calendar year everyone else was already using.

March 25th was one of several conventions: medieval Europe also began the year on December 25th, at Easter, or on September 1st, depending on the place and the period. Other countries moved the year at other times — France in 1564, Scotland in 1600, Venice not until 1797 — so the year on a Continental record also depends on where it was written.

What is the difference between a Julian date and an Old Style date?

Julian refers to the calendar itself; Old Style refers to the way the year was numbered before the legal new year moved to January 1st. They are related, but they describe different things.

The calendar sets the day: a Julian date has to be moved forward to its Gregorian equivalent, by more days the later the century. A record written while the Julian calendar was in force needs that correction before it can be compared with a Gregorian date.

Old Style sets the year: a pre-1752 English or Welsh record from January 1st to March 24th still bears the old year’s number, and the correction is to the year alone.

A date can need both. “5 February 1740/41” in an English register needs the year settled first and the day correction second.

When did different countries adopt the Gregorian calendar?

Adoption occurred at different times by country and territory. Some major examples:

Catholic Europe: many countries adopted the Gregorian calendar in 1582, when Thursday, October 4th (Julian) was followed by Friday, October 15th (Gregorian).

Scotland: changed the legal new year to January 1st in 1600 but retained the Julian calendar until 1752.

England and Wales: 1752, changing both the calendar and the start of the legal year.

The reform only carried the Pope’s authority within the Catholic Church; each state adopted it when it chose by its own law, and Protestant and Orthodox states held out for a century or more rather than accept a papal calendar. Civil adoption did not always carry religious use with it: the Orthodox churches keep the Julian calendar for feasts, which is why an Orthodox Christmas falls on January 7th of the civil calendar.

Beyond Catholic and Protestant Europe, adoption went on into the twentieth century: Japan in 1873, Egypt in 1875, China in 1912, Russia in 1918, Greece in 1923, Turkey in 1926. A fuller list, by country and territory, is available at Wikipedia’s Adoption of the Gregorian calendar.

Adoption dates varied among individual states and territories, particularly in the German and Eastern European regions, and the calendar change and the change to a January 1st new year did not always happen at the same time. The place and date of the record should be considered before converting it.

Should I keep the converted date or the date in the record?

Standard practice is to copy a date exactly as the record gives it and mark the calendar or year system — “3 March 1700 (Julian)”, “10 February 1700 (OS)” — rather than replace it with the converted equivalent. The original form is what a later researcher will find when checking the same register, and a converted date with no note can be mistaken for a transcription error.

A record may write the year short — “40” for 1740 — leaving the century to the reader. The converter does not supply it: a year is entered in four digits, and the year 40 itself as 0040.

Conversion is for comparison. When dates from records using different calendars need to be compared, bringing them onto a single calendar makes the difference between them clear. The converted date can be recorded alongside the original, but it should not replace it without explanation.

A date in a database or a family-tree program is not always the date in the record. Software commonly applies the modern calendar to every date, including those before the place in question adopted it — a proleptic Gregorian date — and a downloaded or copied date may already have been converted by someone else. The record’s own words are the evidence; a converted date is an interpretation of them, and both should be kept.