Learn Hardcore Finnish: Lauantai-iltana meillä on elokuvailta kotona. - On Saturday evening, we have a movie night at home.

lauantai-ilta (Saturday evening) is a fixed type of time expression: day-of-week + part of day. In standard spelling, these are normally written with a hyphen:
- maanantai-ilta, tiistai-aamu, perjantai-yö, etc.
  The case ending then comes at the end: lauantai-iltana (essive).
elokuvailta (movie night) is a more general noun + noun compound:
- elokuva (movie) + ilta (evening) → elokuvailta (movie night)
  These are usually written as one word without a hyphen, unless there is a special reason to add one (clarity, pronunciation, etc.), which is not needed here.

So the hyphen in lauantai-iltana follows a specific convention for calendar-type expressions, not a general rule for all compounds.

What grammatical case is meillä, and why does Finnish use that to mean “we have”?

Meillä is in the adessive case, which often means “on, at, with” or “at the place of”.

me = we
meillä = “at us / at our place / with us”

Finnish usually expresses possession with a locative structure instead of a verb like “to have”:

Minulla on auto. = At me is a car. → “I have a car.”
Sinulla on koira. = At you is a dog. → “You have a dog.”
Meillä on elokuvailta. = At us is a movie night. → “We have a movie night.”

So meillä on X is the normal way to say “we have X”, literally “there is X at our place / with us.”

Why is the verb on (3rd person singular) used with meillä (we)? Shouldn’t it be olemme?

In this structure, meillä on, the verb is not agreeing with me as a subject. Instead, Finnish is using an existential sentence:

[Meillä] on [elokuvailta].
“At us is a movie night.”

Grammatically:

elokuvailta is the logical subject (the thing that “is”).
meillä is an adverbial phrase (“at us”).

In existential sentences in Finnish, the verb olla (“to be”) usually appears in 3rd person singular, regardless of who the possessor is:

Minulla on… (I have…) – verb on
Sinulla on… (You have…) – on
Meillä on… (We have…) – on
Heillä on… (They have…) – on

That’s why you don’t say me olemme elokuvailta; that would mean “we are (a) movie night,” which is nonsense.

What does elokuvailta mean exactly, and how is it formed?

Elokuvailta is a compound noun:

elokuva = a movie, film
ilta = evening

Together:

elokuvailta = “movie evening” → idiomatically “movie night”

It refers to a specific kind of event: an evening that is dedicated to watching films. In the sentence, it is in the nominative singular, acting as the thing that “we have”:

meillä on elokuvailta = we have a movie night

Finnish makes many such compounds:

saunailta = sauna night
peli-ilta / pelailta = game night
työilta = work evening (an evening spent working)

What does kotona literally mean, and what case is it?

Kotona comes from koti (home).

The form kotona is an inessive-like locative meaning “at home”:

koti = home
kotona = at home

For koti, the local cases are a little irregular:

kotona = at home (like an inessive meaning “in/at”)
kotiin = to home (direction towards, like illative “into”)
kotoa = from home (direction away from, like elative “out of”)

So kotona in the sentence simply tells you where the movie night takes place: at home.

If meillä already suggests “at our place”, why do we also need kotona (“at home”)?

Meillä and kotona add slightly different meanings:

meillä = “at our place / with us”
- focuses on us as the hosts / possessors of the event
- meillä on elokuvailta = “we have / we are having a movie night” (it’s our event)
kotona = “at home”
- specifies the physical location of the event

So:

Lauantai-iltana meillä on elokuvailta.
→ On Saturday evening we have a movie night (somewhere, not specified).
Lauantai-iltana meillä on elokuvailta kotona.
→ On Saturday evening we have a movie night at home (not at a cinema, not at a friend’s place, etc.).

Both together say: we are the ones having/hosting it, and it takes place at home.

Could the sentence be reordered, and would that change the meaning?

Yes, Finnish word order is flexible; the basic meaning stays the same but emphasis shifts. All of these are grammatically fine:

Lauantai-iltana meillä on elokuvailta kotona.
Neutral: time first; “On Saturday evening, we have a movie night at home.”
Meillä on lauantai-iltana elokuvailta kotona.
Slightly more emphasis on meillä (we are the ones who have it), time in the middle.
Meillä on elokuvailta kotona lauantai-iltana.
Sounds a bit heavier; time comes last, as an afterthought.
Kotona meillä on lauantai-iltana elokuvailta.
Emphasizes at home as the contrast (as opposed to somewhere else).

You can move time, place, and possessor around mainly to highlight what’s important in context. The core facts (Saturday evening, we have, movie night, at home) don’t change.

Could you say “Lauantai-iltana me katsomme elokuvia kotona” instead? How is that different from “meillä on elokuvailta”?

Yes, you can say:

Lauantai-iltana me katsomme elokuvia kotona.
= “On Saturday evening we watch movies at home.”

Difference in nuance:

meillä on elokuvailta
- Presents it as a named event or occasion (“movie night”).
- Suggests something a bit more planned or special.
me katsomme elokuvia
- Just describes the activity (we watch movies).
- Neutral statement of what happens, without framing it as an “event”.

So elokuvailta sounds like “It’s our movie night (maybe snacks, tradition, etc.)”, while katsomme elokuvia just says what you do.

Why are there no words like “a / the” before elokuvailta or koti in Finnish?

Finnish has no articles (no direct equivalents of a, an, the). Nouns appear “bare”:

elokuvailta can mean “a movie night” or “the movie night” depending on context.
koti / kotona can correspond to “home”, “the home”, “at home”, etc.

Which English article you choose in translation is decided by:

context,
whether it’s already known/specific,
whether you mean something general or a particular instance.

In the sentence Lauantai-iltana meillä on elokuvailta kotona, English naturally adds “a”:

“On Saturday evening we have a movie night at home.”

What tense is on here, and how can it talk about a future Saturday evening?

On is the present tense of olla (to be).

Finnish often uses the simple present to talk about the near future, especially when the future event is scheduled, planned, or certain:

Huomenna meillä on kokous. = Tomorrow we have a meeting.
Ensi viikolla on loma. = Next week (there) is a holiday.

So:

Lauantai-iltana meillä on elokuvailta kotona.
Literally present tense, but in English you’d normally say:
“On Saturday evening we’re having a movie night at home.”

Are there other common time expressions that use the same -na ending as lauantai-iltana?

Yes. The essive case (-na / -nä) is very common in time expressions. Examples:

maanantaina = on Monday
tiistaina = on Tuesday
jouluna = at Christmas
pääsiäisenä = at Easter
syntymäpäivänäsi = on your birthday
kesäiltana = on a summer evening
talvella vs. talvena – both exist, with slightly different nuances

So lauantai-iltana fits nicely into this pattern: on Saturday evening.