HELP! A liturgy nerd is building a digital-calendar-generator for the TLM

Can you brilliant liturgy nerds help this… liturgy nerd cum computer geek?


From a reader:

Hi father Z!

I have spent the last two weeks constructing a digital-calendar-generator for the TLM/-62 (in Swedish, with celebrations according to the calendar found inside the new TLM handbook – that by the way even has a foreword by our bishop). It can now generate the entire liturgical calendar for any given year for at least the next 200 years (if I’ve constructed it correctly).

Now I’d be very happy to receive any help to correct the details in the generator – from you, someone you could direct me to, or through your blog commenters (if you choose to forward this to your readership).

As I am now finalising the generator I have come to doubt that I have treated the lower-rank celebrations correctly.

The printed calendar that I’ve taken my information from presents the lower rankings using the old system (S, Sd, D, Dm) and explains that all of them except S become ‘3rd class’ in the “new” JXXIII system. What I wonder is:

1. When a Simplex (or are they supposed to be referred to as ‘4th class’?) falls during Epiphanytide or ‘after Easter’

a. Is a proper liturgical color to be used or is the color of the season to be used (the latter is how I have interpreted Commemorations to work)?

b. is it a mandatory or optional celebration (like ‘opt. Mem’ in the new rite)?

2. If the same kind of celebration falls during Advent or Lent:

a & b as above

c. Does its rank somehow reduce to Commemoration (or do they even disappear) because of the higher rank of Lenten/Advent ferias?

3. Are ‘3rd class’ celebrations ever affected in other ways than being stricken (because of collision with a higher ranked celebration)?

My questions probably sound like I don’t know a thing about these things, which is not false – I mainly want to have a working digital calendar for the old rite, since I am a liturgical nerd, not expert :)

Pax, and forgive my bad English

Okay, friends!  Get to work!


About Fr. John Zuhlsdorf

Fr. Z is the guy who runs this blog. o{]:¬)
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  1. jasoncpetty says:

    So he’s sort of asking for a long-form version of Divinum Officium which, I think only gives a year at a time? Does Divinum Officium address these particular issues in its calendar? I use it on my mobile if I’m at Mass without a missal and it’s pretty great.

  2. bvb says:

    I’ve actually been contemplating doing something similar. Might you be able to post the code, please?

  3. wolfeken says:

    I would recommend getting a good Ordo, such as the one published by the FSSP, and reading it cover to cover:

    There are dozens, if not hundreds, of nuances, clarifications and distinctions that go into the plotting of the liturgical year. Look no further than Immaculate Conception 2013 to see just how complicated things can get.

  4. OrthodoxChick says:

    I’m so glad that someone asked about this because I’m having trouble figuring it out. I am using a St. Joseph missal from 1955 that I inherited from a grand-aunt. If I post what it says in my missal, can someone please explain what changed between 1955 and 1962? If things had just been “reformed” liturgically in 1955, why did we need a council to come along and do more reforming again only 7 years later? Not that I have any right or authority to question it. What’s done is done, but I’d just like to understand it better. Not looking for rabbit hole debates. I’m more looking for a liturgical history lesson.

    My 1955 missal says this under the heading, “The Classification of Feasts”:

    “According to their liturgical rank, feasts are graded, DOUBLE 1ST CLASS, DOUBLE 2ND CLASS, DOUBLE MAJOR, DOUBLE, and SIMPLE. When two or more feasts happen to fall on the same day, the feast of the higher grade will take precedence. The Mass, consequently, will be of that feast. The lesser feast may be transferred to a later date, or, more usually, it will receive a commemoration, ie., its Prayer, Secret and Postcommunion will be recited in the Mass of the preferred feast. The commemorations which must never be omitted and which have absolute precedence are those:
    (a) of any Sunday,
    (b) of a 1st Class feast,
    (c) of the ferial days of Lent and of Advent,
    (d) of the Ember Days of September, and
    (e) of the Greater Litanies.

    Other commemorations which may occur are admitted in such a way that there are never more than three Prayers, Secrets and Postcommunions. Further, besides the foregoing commemorations, and after these, the rule for commemorations is as follows:

    on Sundays of the 1st Class, on 1st Class feasts, on privileged ferial days and vigils, and also sung Masses or solemn votive Masses, no commemoration is admitted; on all other days, either feast days or ferial days, only two commemorations are admitted.”

  5. Kathleen10 says:

    I can’t even figure out the questions.

  6. NBW says:

    @Orthodox Chick, that is an interesting question. My mom has been complaining that she can’t follow the Tridentine 1962 Mass because it doesn’t match up with her 1946 missal. Perhaps Fr. Z could shed some light on the matter.

  7. Deo volente says:

    I have been posting links to the Propers for the TLM Mass for each day for several years (always staying one day in advance for those in the Far East. I learned that it is essential to use a good Ordo and the one I use is the one from the F.S.S.P. which is pretty standard. The Ordo classifies each day by the name, Commemorations (if any), the Class and Color of vestments and whether or not the Gloria and Creed are to be said. After posting this info, I usually look up this website:

    In 99% of cases, the DivinumOfficium site is spot on as judged by comparing the readings with those in the Baronius Summorum Pontificum Missal which has an Imprimatur from Bishop-Emeritus Fabian Bruskewitz.

    If you’ll note, the site

    has a link next to the daily Propers reading “Kalendarium”

    If you click that link, you are taken to this page:

    Note that under “Hodie”, one can click any time between 2009 to 2018 and the Mass for the same date will appear. One can also use another month or different day of the month.

    The problem in coding such a huge enterprise is in “privileged Commemorations” which will vary (as Wolfeken points out). So, static html encoded sites may give the correct readings for a particular feast day, but may have the incorrect commemoration if a moveable feast has happened.

    I know that the amazing Hungarian man who began the DivinumOfficium site worked for years on it, and there is now a huge cohort of people updating the site to bring it in line with the Missale Romanum for 1962 (the John XXIII edition).

    The site below is excellent for simply knowing which Mass is celebrated for Feasts of Saints and Votive Masses.

    This site is recommended by Una Voce, but note that it separates Sundays from the Feasts for Saints.

    I think the best alternative is to perhaps contact those at the DivinumOfficium site, and ask the questions that are posed here. It would be pretty amazing to have an accurate Ordo with Commemorations for something like 20 years let alone 200! The permutations are astronomical!


  8. theophilus says:

    I already created a TLM calendar generator in my free windows desktop application at

    It does the next 50 years though… However, I doubt our current computing architectures will last that long.

    I will soon port it to the website below since I am presently burned out with desktop apps :)

  9. Jerry says:

    re: wolfeken – ” Look no further than Immaculate Conception 2013 to see just how complicated things can get.”

    The Immaculate Conception? Or the Annunciation? While the former is on a Sunday in Advent, it is being celebrated on the proper day; the latter was transferred 2 weeks due to conflicts with Holy Week and the Easter Octave.

  10. aquinas138 says:

    I begin by saying I am much more knowledgable about the Office than Mass.

    1. Simplex feasts became mere commemorations at Lauds and at Low Masses.
    a. The color depends on which Mass is said. The days during Epiphanytide and Eastertide are of the IV Class. The Office is always of the season, with a commemoration of the Saint in question at Lauds, but at Low Masses, the Mass may be of the season or of the commemoration – that would determine the liturgical color.
    b. Everything entered in the calendar is mandatory, but III class days and commemorations are omitted much more often than in pre-1960 rubrics.

    2. On ferias of Advent and Lent, the commemorations are always made at Lauds. They are also commemorated on II class days, unless a privileged commemoration must be made – II Class days only admit one commemoration maximum.

    3. III Class feasts are reduced to a mere commemoration at Lauds if they occur with a II Class feast, but are omitted in occurrence with a II Class Sunday. They are always omitted in occurrence (and concurrence) with any I Class day. In the case of occurrence with another III Class day, it depends. In Advent, the feast is celebrated, but the feria is commemorated at BOTH Lauds and Vespers. In Lent however, the feria is celebrated and the feast commemorated at Lauds only.

  11. aquinas138 says:

    OrthodoxChick –

    The old distinction between double-semidouble-simple is complex because it only indirectly indicates rank – it is actually referring to rite, which refers mainly to whether the antiphons were sung entire before the psalms (double) in the Office or merely intoned (simple). Additionally, with a few exceptions (notably Easter and Pentecost), double feasts have 9 lessons, simple feasts have 3 lessons. The rank of semidouble mixed the two – merely intoned antiphons but 9 lessons.

    The close connection between relative importance of a liturgical day and the rite used led to the distinctions of rite being used practically as ranks, but that was never a very clean system. Over the centuries, as the feasts of saints proliferated and moved “up the chain” from simples to semidoubles and doubles, the sheer number of doubles required finer gradation, leading to the eventual distinction between doubles of the I Class, doubles of the II Class, greater doubles, and (lesser) doubles.

    The 1955 reforms, in short, eliminated the rank of semidouble and limited the number of commemorations. Former simples are reduced to commemorations, and former semidoubles are reduced to a simple. Sundays, which with the lone exception of Low Sunday, were always semidouble, were raised to doubles, but were permitted to continue to be said as if semidouble, since the Breviary did not print the full antiphon before the psalms.

    The 1960 reforms introduced a new classification system of liturgical days: I Class, II Class, III Class, IV Class and Commemorations. Doubles of the I Class became I Class; Doubles of the II Class became II Class; Greater Doubles, Doubles and Semidoubles became III Class; and Simples became Commemorations. The old tripartite system of Sundays of the I Class, Sundays of the II Class, and Lesser Sundays was simplified into a bipartite system of I and II Class Sundays. Several feasts were deleted from the calendar, and many of the feasts of apparitions of the BVM, which were usually Greater Doubles, were reduced to commemorations instead of the expected III Class.

  12. Rachel Pineda says:

    @ Deo Volente:
    I have used your website several times and it has been very helpful. Thank you very much.

  13. OrthodoxChick says:

    Aquinas138, Thank you so very much for your in-depth explanations. It’s beginning to make sense to me!

    Deo Volente, great blog! I just bookmarked it. I’m also now following you on twitter and friended you on FB.

    Thank you both for your help!

  14. wolfeken says:

    Jerry — Immaculate Conception.

    The traditional Latin Mass will indeed have the feast of the Immaculate Conception on Sunday, 8 December 2013, with the Second Sunday of Advent commemorated (2nd collect, 2nd secret and 2nd postcommunion). The novus ordo will observe the Second Sunday of Advent on 8 December, bumping (!) the feast of the Immaculate Conception to 9 December while lifting (?) the obligation.

    Needless to say, it will cause a lot of confusion in mixed parishes. Hence, the need for a good Ordo (FSSP) to guide priests who do not have the time to research rubrics concerning which Mass wins in a battle between two first class feasts.

  15. I have been searching for a useful working iCal for all the holydays, both old and new to load into my Hotmail/ calendar, and other vehicles. None exist as far as I can tell after much searching. Part of the maintenance problem is the movable feast of Easter and hitching in the many movable observances and therefore, the calendars come to an end without constant updates by the calendar creator. I would love to see a solution, even if its not perfectly detailed – thanks to all!!
    theophilus: I’m not having any luck accessing your calendar. Is there a direct link? Or is it my MAC?

    aquinas138: Thank you for that excellent explanation. verrrrrry interrrrrestink. How symbolic of the condition of the Church.
    Back when St Joseph was added to the Canon, people squawked because up to then the Church only included Martyrs [the best assurance of sainthood]. As some feared then, that allowance was symptomatic of many changes that have not stopped even up to now. Although some changes may have been made in good faith, it looks like progressives took advantage of the openness to change.
    The roots of these changes are more than just the issues with Vatican II and go way back.
    Ironic how the Papal 1794 Papal Bull Auctorem Fidei condemned everything we are experiencing today from ambiguity, to changing Church disciplines, to over-extensions of the authority of Bishops, and tons more. Gee, almost like our Church saw it all coming.

  16. Deo volente says:


    This is not iCal, but is a link to the F.S.S.P. Seminary in Denton, Nebraska:

    It could be used as a simple hyperlink giving you the Ordo for the day. When it was updated in January, the F.S.S.P. used the same link so the Ordo didn’t suddenly disappear. Hope that helps!


  17. There are lotsa lists of holydays all over the web, but at least your FSSP link is hitched to liturgical definitions. Thanks D.V. :-) I still long for a nice iCal to feed my apps [whimper].

  18. aquinas138 says:

    Tina in Ashburn:

    I have a Google calendar, currently complete only through 2015, for the 1960 rubrics, with the local feasts for the USA incorporated. You can find the calendar at

    I haven’t updated in a while, but I have written some Applescripts to generate the calendar in iCal; it usually takes a little manual cleanup to handle the occasional translation of a feast, but it doesn’t take long to update. If it doesn’t work for you or you have questions about it, you can contact me at

    aquinas138 [at] gmail [dot] com

  19. Fr Z, thank you for this post. Here’s hoping there’s additional helpful digital calendar info here, whether its iCal info or a macro that generates a digital calendar or whatever.
    aquinas138: thank you, that is so nice of you! Yes, that calendar looks good.

    There are some calendars at where anyone can share what they create for feeding an online calendar, to subscribe or import. There are too few Catholic calendars, and invariably something’s missing, or the calendar simply ends, is abandoned.
    These are public so if you choose to upload a calendar that you created, be sure to exclude personal stuff before sharing.

    I used to have so much fun creating macros back when I was a programmer, I could even dismantle viruses, trojans and such. Alas, that’s all forgotten. Certainly there must be somebody out there who can use similar methods for a never-ending iCal calendar and which can include the movable feasts?

    FWIW, iPieta has an awesome calendar, containing both the OF and EF. However, no iCal for the online calendar.

    Any other ideas or sites?

  20. Fr Jackson says:

    I have an excel spreadsheet that attempts to use macros to do something similar to what you have described. It works rather well, but it is in French. I’ll be happy to send it to you. (Fr Z has my email if he is willing serve as intermediary?)

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