When is Easter 2013? And Why?

Easter is springing up a bit earlier this year than last and if you’re confused about how the dates are calculated, you’re not alone. Searches for “when is Easter” are peaking, according to Google Trends, and although the date is easy enough to find, the reason behind it is somewhat convoluted.

This year, the holiday falls on Sunday, March 31. Last year it rolled around on April 8. Next year? April 20. 

In 325 A.D., Catholic Church officials decided Easter would be celebrated on the first Sunday after the first full moon after the March equinox. Fairly straightforward.

Calculating the dates into the future, the church relied on tables of predictions that listed full moon dates thousands of years in the future (not actual dates of full moons). These predicted dates are called Ecclesiastical Full Moons or EFMs.

And instead of using the actual March equinox, which can shift, Easter calculations always use March 21.

To be precise: Easter falls on the first Sunday after the first EFM after March 20. 

Determining a date for Easter wasn’t really that quick and easy – 1,200 years later, in the 17th Century, the Catholic Church wound up introducing a new calendar because the dates of the equinox and other astronomical events were drifting through the seasons. 

The church cut 10 days off of the Julian Calendar, added a leap year and introduced the new and improved Gregorian calendar. In some traditions (including Orthodox Christian churches), Easter is still determined using the Julian calendar. The dates of Easter can vary substantially between traditions.

So here we are.

According to Easter algorithm, the holiday can fall anywhere between March 22 and April 25. Barring some unforeseen advances in medicine or time travel, if you’re reading this, you’ve already experienced the earliest Easter you will in your lifetime. In 2008, the holiday fell on March 23. It hadn’t been that early since 1913 and won’t come that early again until 2160.

If you like extremes, however, look forward to 2038 – that’s the next year Easter will fall on April 25.

Want to know what date Easter will fall on in, say, 2300? Check this handy tool on the United States Naval Observatory's website. The site also has a fairly comprehensive history of the calculation of the date of Easter.