Because Easter is the longest liturgical season in the Catholic Church

Which religious season is longer, Christmas or Easter? Well, Easter Sunday is only one day, while there are 12 Christmas days, right? Yes and no. To answer the question, we need to dig a little deeper.

The 12 days of Christmas and the Christmas period
The Christmas period actually lasts 40 days, from Christmas day until Christmas, the presentation party, on February 2nd. The 12 days of Christmas refer to the most festive part of the season, from Christmas day to Epiphany.

What is the octave of Easter?
In the same way, the period from Easter Sunday to Sunday of Divine Mercy (the Sunday after Easter Sunday) is a particularly joyful moment. The Catholic Church refers to these eight days (counting both Easter Sunday and Sunday of Divine Mercy) as the Easter octave. (Octave is also sometimes used to indicate the eighth day, or the Sunday of Divine Mercy, instead of the entire eight-day period).

Every day in the octave of Easter is so important that it is treated as a continuation of Easter Sunday itself. For this reason, fasting is not allowed during the Easter octave (since fasting has always been prohibited on Sunday) and on Friday after Easter, the normal obligation to abstain from meat on Friday is canceled.

How many days does the Easter season last?
But the Easter season does not end after the octave of Easter: since Easter is the most important holiday of the Christian calendar, even more important than Christmas, the Easter season continues for 50 days, through the Ascension of Our Lord on Pentecost Sunday , seven whole weeks after Easter Sunday! In fact, in order to fulfill our Easter duty (the obligation to receive Communion at least once during the Easter period), the Easter period extends a little further, up to Trinity Sunday, the first Sunday after Pentecost.

However, the last week is not counted in the normal Easter period.

How many days are between Easter and Pentecost?
If Pentecost Sunday is the seventh Sunday after Easter Sunday, shouldn't that mean that the Easter period only lasts 49 days? After all, seven weeks times seven days are 49 days, right?

There are no problems with your math. But just as we count both Easter Sunday and Sunday of Divine Mercy in the octave of Easter, so we also count Easter Sunday and Pentecost Sunday in the 50 days of the Easter period.

Happy Easter
So even after Easter Sunday has passed and the Easter octave has passed, continue to celebrate and wish your friends a happy Easter. As St. John Chrysostom reminds us in his famous Easter homily, read in the Eastern Catholic and Eastern Orthodox Easter churches, Christ destroyed death and is now the "feast of faith".