Helpful Calendar Conversion Tools for Genealogists

By Nick D'Alto Premium

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Written by Nick D’Alto, unless otherwise noted

In today’s society, we’re slaves to the clock (remember the kerfuffle caused by the shift in daylight-saving time?). Our ancestors, on the other hand, were far more flexible about timekeeping. The average villager in the Middle Ages, for example, had no idea what year it was — it simply wasn’t relevant to his life. Even centuries later, governments and churches changed calendars to move holy days and mark political revolution. In our forebears’ world, the date might’ve been different in places just a hundred miles apart.

Naturally, this causes all kinds of headaches for family historians. How are you to record your ancestor’s age if the birth date noted by the church clerk was based on their calendar, not yours? Or suppose you find a letter that says Great-grandpa Fred died “last Saturday,” or you have Great-aunt Edna’s marriage year and age, but no birth date.

We’ll help you solve these dilemmas and use date information to your genealogical advantage with a variety of calendars, converters and calculators. You’d be surprised how much more effective you can be in discovering your family’s past. So let’s make a date to get started — how about now?

The Julian vs. the Gregorian Calendar

There’s a pope in your family tree: Gregory XIII (1502-1585). He authorized the Gregorian calendar—the international standard today—to replace the old Julian calendar dating back to Caesar’s time. Under that calendar, a slight discrepancy in the math eventually caused Easter, whose date is based on lunar cycles and the first day of spring, to drift into the wrong season.

Gregory’s calendar restored religious holidays to their proper dates. To “reset” time, he adjusted leap year, then ordered 10 days removed from the calendar. So Oct. 5, 1582, instantly became Oct. 15. According to legend, villagers in many towns rioted, demanding their 10 days back.

That might make you chuckle—until you realize this 16th-century conversion likely affected your family’s records. Though some countries adopted the Gregorian system quickly, many retained variations of the old Julian system. For example, England and its American colonies didn’t “go Gregorian” until 1752, so they lost an extra day.

No Colonial ancestors? You’re still not off the hook: The Julian problem can affect your international family tree well into the 20th century. Russia didn’t convert completely from Julian time until 1918; Romania and Yugoslavia switched in 1919. Greece stayed on the Julian calendar until 1923. In these late-adopting countries, fairly recent marriage certificates, immigration documents and even postmarks may be dated almost two weeks behind calendars used elsewhere at the time. Your German kin could’ve left Berlin Sept. 7, 1909, yet reached Moscow Sept. 6.

To fix these date problems, first identify when the country in question switched calendars using this list of nations and adoption dates. Then, consult a “New Style” Julian Converter like Rosetta Calendar or Converting Between Julian and Gregorian Calendar in One Step from Stephen Morse. Just type in your Julian date and the tool will reckon it against our modern calendar.

Genealogy research issues with date conversions

Britain’s adoption of the Gregorian calendar in 1752 could require some revolutionary calendar work for your Colonial ancestry. Some examples of problems you might encounter:

  • American dates before Sept. 2, 1752, are Julian dates. That makes them 11 days behind the rest of Europe at that time — and the calendar we use today. (Pope Gregory’s calendar subtracted only 10 days, but the Colonies adopted it so late, they had even more catching up to do.) For example, we celebrate Washington’s birthday Feb. 22, but he was actually born Feb. 11.
  • History says Washington was born in 1732, but he would say 1731. In those days, the English year began not on Jan. 1, but March 25 (called Lady Day). For the genealogist, this can cause real confusion: Say your Boston relative was born Feb. 23, 1747, and baptized April 23, 1748. Ordinarily, we would count that as 14 months. In fact, it’s just two months—the calendar at the time “turned” March 26.
  • Your kin’s birth date might appear on records as “Feb. 23, 1747/8.” Was the clerk uncertain of the year? No, some Colonial clerks tried to record both the Julian and Gregorian years. The date also might show up as 1747OS (for “Old Style”) or 1748NS (“New Style”). For example, Thomas Jefferson’s epitaph reads “born April 2, 1743 OS, died July 4, 1826.” These double dates can turn up anywhere the years bridge old and new timekeeping.

Our best advice: Don’t convert in your head. If you find a pre-1752 date, write it exactly as you found it. Then access an Old Style-New Style Julian converter—not just any Julian converter; it also must account for old New Year’s Days. Ian’s English Calendar hosts a good one; just type in the Julian date; a modern Gregorian date pops out.

Using perpetual calendars

Suppose a letter dated Nov. 12, 1848, says your fifth cousin Orville was born last Tuesday. What was his birth date?

Perpetual calendar to the rescue: This type of calendar lets you identify the day of the week for any date. Most perpetual calendars work for 100 years (hence, the nickname “100-year calendars”). They’re simple to use: You generally look up a code for the year you want, then consult a calendar that corresponds to that code. To go all the way back to the 17th century, visit and click the tiny Scroll Up link above the right corner of the calendar.

You also can use a variety of online perpetual calendars that let you type in a date and learn:

  • The right date: Date calculators such as the Calendar Calculator give you the right calendar for any month, in any year. If you key in November 1848, you can find the 12th and count back to “last Tuesday” to learn cousin Orville arrived Nov. 7.
  • The day of the week: Add another snippet of detail to births, immigrations, deaths and other events in your family history using the day-of-the-week converter at Just key in any date to get the day. You may be surprised to learn events such as weddings and baptisms didn’t always take place Saturday or Sunday. Amish, for example, wed only on Tuesday or Thursday.
  • The right year: A scribbled “Thursday, Jan. 28th” on a Civil War letter dates it to 1864. A date finder, such as the University of Notre Dame’s Perpetual Calendar, reveals that’s the only year during the Civil War when Jan. 28 fell on a Thursday.
  • A birth date: “Died March 7, 1826, aged 61 yrs, 8 mos, 11 days.” Old tombstones often lack a birth date, but a lifespan calculator can tell you when your great-great-great grandfather was born—just enter the age (years, months, days) and the death date at Ancestor Search. In this case, your forebear was born June 24, 1764 (plus or minus a few days to account for stonecarvers’ varied formulas in calculating the deceased’s age). Try this with ages shown in a census, too.
  • An age: How old was Great-grandma on her wedding day? If you know her birth date and wedding date, use a calculator such as It’ll give you the time between any two family events.

All-around props go to Herb Weiner’s Calendar Calculator, a great tool that lets you display any month or year; ask what years June 7, say, happened on a Thursday; convert dates from one region’s calendar to another’s; and perform a variety of other tasks.

Religious holidays and traditions

Every ethnic tradition has rich calendar-based lore, usually tied to religious observances. These often are “floating holidays” — they didn’t happen the same date every year. Your old German kin partied the Tuesday before Lent, called Fastnacht. For African Americans, Pinkster (Pentecost Sunday) marked a day for gathering and celebration. Old documents are sometimes dated according to these religious observances (for example, the Feast of St. Sebastian) rather than the secular date. Because our day and month names derive from pagan gods (ie, Thursday comes from “Thor’s day”), Amish refused to use them, preferring numbers instead. The date 4d4m means fourth day, fourth month: April 4.

You can use religious calendar tools to discover family traditions and calculate birth dates by:

  • Finding floating holidays: Say your first American-born relative came into the world Easter Sunday, 1881. What date was he born? The Eastern Orthodox Church uses the Julian calendar to determine its holy days, which is why Orthodox Christmas falls on Jan. 7. You’ll find this and other major dates at GMArts. Similarly, Jews follow the Hebrew calendar — visit Steve Morse’s website (scroll down to Calendars) for a printable version and tools to convert both Hebrew calendar dates and tombstone dates.
  • Learning “name days”: Your great-aunt born Jan. 2 was named Agnes; a sixth cousin Cosmo was born Sept. 27. Calendars may be behind their monikers: Catholics in many nations name a child after the saint on whose feast day he or she was born. But even if your ancestor Andrew Withersby wasn’t born Nov. 10 — the feast day of St. Andrew — his family may have celebrated that day with gifts and well-wishes.

    Naming calendars can reveal your family’s cultural traditions and let you guess unknown birth dates. But over time, church reforms have changed the dates associated with different names. To trace pre-1955 names, you need a traditional calendar such as from Wikipedia.

    The Eastern Orthodox naming calendar is similar to that of Catholics. And though Anglicans don’t venerate saints, they observe special days for notable historical figures; see the Church of England’s website.

    Some nations formally adopted name-day calendars. See Sweden’s on Wikipedia; visit Behind the Name for other countries’ calendars.

Using a calendar to trace ancestors

Say your forebears reached Ellis Island in January 1894, married in July, and bought a home in October. A busy time for them! At, you can select an 1894 calendar, customize its appearance, and print it. Then fill in the important events in your ancestors’ lives—it’s almost like finding like your relative’s day planner. If you have family records that cover date ranges (diaries, store ledgers, court documents), you can compare entries against that year’s calendar to figure out missing dates or explain lulls.

You may even be able to follow ancestors’ lives using the calendar on your wall now—a 2007 calendar works perfectly for 1894, 1906 and 1917. To match other years, visit If you’ve ever wished to return to the days of your ancestors, the calendar is a great place to start.

Recording dates in genealogy research

To keep dates in your genealogical research accurate, follow these guidelines when you make a translation:

  • Record all dates exactly as you found them in a document.
  • Next to that, write any conversions you make in square brackets [ ], and note the method and tool you used, such as “Julian conversion to Gregorian, <>.”
  • When a date is less certain, use these symbols alongside it: c. or abt. for about, bef. for before, aft. for after, bet. for between.
  • In US records, 8/11/1928 is Aug. 11, 1928. In European records, it’s Nov. 8.
  • On your genealogy charts, record dates European-style and in long form: 23 February 1887.

A version of this article appeared in the November 2007 issue of Family Tree Magazine.

Other Online Calendar Tools

Ancestor Search: Genealogy Calculator and Tools: This website has 13 tools to calculate ages and birthdates based on the dates on a tombstone. Share tools, which pop up on the left side of the website, allow you to print the information you find for easy reference later, as well as post it to social media.

Calculating Birth Year from Census Information: This site from Rose-Anne’s Genealogy Resources lets you choose a US census year, then match the reported age of your ancestor with the year (or year range, in the case of pre-1850 censuses) when he or she was born. As the page cautions, a reported age may be inconsistent from census to census, based on the actual birth date and the date the census was taken.

French Revolutionary Calendar: France adopted a new calendar for 12 years after the 1789 French Revolution, and then again for 18 days in 1871. This calendar stripped out religious and royal influences, replacing days named after Roman Catholic saints with the names of plants, tools and animals. Years were in Roman numerals, and months also were renamed. This tool displays today’s date in accordance with the antiquated French system, and provides a conversion for any date since Sept. 21, 1792.

Calculation of the Ecclesiastical Calendar
Need to know what day Easter or another religious holiday was held in a certain year? The Ecclesiastical Calendar calculates Western and Orthodox dates when you enter a year. For instance, type 1920 for the Western calendar, and you’ll get dates for Easter, All Saints’ Day, Christmas and more. Another calendar tool here, the American Secular Holidays Calendar, gives dates for federal holidays and events such as Election Day.

GENUKI: Dates for Easter Sunday and Perpetual Calendar, 1550-2049: GENUKI is a reference and resource website for UK and Irish genealogy research. This tool for Easter dates in Great Britain and her colonies is fairly straightforward: It’s simply a list of dates on which Easter fell from the years 1550 to 2049. Click on the year you’re interested in, and you’ll get a calendar for that year. Note that this calendar doesn’t include Scotland from 1600 to 1752.

Hebcal Jewish Calendar: Hebcal is a free Jewish calendar and holiday site that converts Hebrew calendar dates to Gregorian and provides a customizable Gregorian or Hebrew holiday calendar from the year 1 to 9999. You can download the calendar to Outlook, Google or your iPhone. Use it for genealogy or other needs, such as Shabbat times and Torah readings.

Old Style and New Style Dates for the Quaker Calendar: This reference tool is for those with Religious Society of Friends (commonly referred to as Quaker) roots. Quakers didn’t use names to refer to months, as our non-Quaker ancestors did. This can become confusing, especially when researching ancestors before England switched from the Julian to the Gregorian calendar. This tool can help you track these calendar changes (hint: March becomes January).  

One-Step Web Pages by Stephen P. Morse: Calendar Tools: Many genealogists are familiar with Stephen P. Morse’s flexible One-Step forms for searching databases such as Ellis Island passenger arrival records, but his site’s other tools can benefit researchers, too. The Perpetual Calendar page lets you look back hundreds of years at dates in the Gregorian and Julian calendars. Other tools include an Elapsed Time calculator to help you determine an ancestor’s birth date based on ages and dates in records; a “When Did … ?” calculator to make such discoveries as what day a birthday fell in any given year; a Tombstone Dates calculator for deciphering Hebrew tombstones, and Muslim, French, Jewish, Julian and other calendar converters.

Wolfram|Alpha: Wolfram|Alpha is a search engine with some unique, useful features. Instead of searching the web for the words you type, it answers your questions. Let’s say you find a newspaper obituary dated Aug. 15, 1876, that says your ancestor died “last Tuesday.” You can type into Wolfram|Alpha’s search engine:  Tuesday before August 15, 1876.Wolfram|Alpha will not only give you the date you want, Aug. 8, 1876, but will also tell you if it was a holiday and what other important events happened that day. Wolfram|Alpha converts Old Style and New Style calendar dates, computes ancestral relationships and helps you decipher handwriting. You can read more about this search engine at Must Have Genealogy Tools From Wolfram|Alpha.

Written by Gena Philibert-Ortega

A version of this article appeared in the July/August 2014 Family Tree Magazine.

Most modern countries use the Gregorian calendar, but it wasn’t always that way. Here’s when each country adopted it, and why it matters for researchers.