Everything I’ve found says that Sundays aren’t part of Lent. From this on
EWTN’s site (it explains the 40-days part too further down on the site):
To this on
Wikipedia:
Actually every definition I found of Lent said Sunday’s weren’t included.
Well, I think we’re getting caught up in a little bit of a semantical loop. I think the central argument is should continue in our fasting and abstinence on the Sundays of Lent. It seems to me that the jury has pretty much come down on the side that self-denial during Lent is not required. It is voluntary. I’ve been all over the Catholic Catechism due to an earlier post where I got some things really wrong.

And, indeed, all Fridays are supposed to be like mini-Lents. Still, even in that particular part of the Catechism, it says that self-denial is voluntary. The Catechism also describes Sunday as a Holy Day of Obligation and specifically states that it is a day for leisure and celebration. There are, of course, a bunch of caveats, but generally, IMHO, the argument that because Sunday is a celebration, a mini-Easter if you will, fasting and self-denial may be inappropriate. I maintain that since it is totally voluntary whether or not to practice self-denial as a part of our Lenten observance, the decision of whether or not to maintain our observance on Sunday is also a matter of personal choice.
Now, Sundays are excluded in terms of counting the 40 days of Lent. So, in that sense, they are excluded from Lent. However, I didn’t find anything, except within the context of counting the 40 days, that said that Sundays are excluded. I will also submit some circumstantial evidence. The Liturgical Calendar says that today, Sunday, Feb. 21st, is the First Sunday of Lent. It further refers to all the Sundays before Palm Sunday as the 2nd Sunday, third Sunday, etc., of Lent. So, it’s an inference on my part but I think it stands up. Again, I think we’re getting caught up in a word game. I think we basically agree. BTW, I am maintaining my regimen of Self-Denial today. I get joy from it.
Finally, I think this was part of someone elses post, but man I’ve got stuff to do!

I included links below to support my rantings above as well as the following assertion. Lent ends at the Holy Mass of the Lord’s Supper on Holy or, as I prefer, Maundy Thursday. The Tridium follows, which ends on Easter Sunday. Easter Sunday begins the Season of Easter which runs through Pentacost. After that, it’s ordinary time until Advent.
Here is some supporting evidence:
catholic-catechism.com/ccc_1438.htm
CCC 1438 The seasons and days of penance in the course of the liturgical year (Lent, and each Friday in memory of the death of the Lord) are intense moments of the Church’s penitential practice.1 These times are particularly appropriate for spiritual exercises, penitential liturgies, pilgrimages as signs of penance, voluntary self-denial such as fasting and almsgiving, and fraternal sharing (charitable and missionary works).
1 Cf. SC 109-110; CIC, cann. 1249-1253; CCEO, Cann. 880-883.
americancatholic.org/newsletters/CU/ac0302.asp#F8