Learn Hardcore Italian: L’ultimo treno è in ritardo.

Feminine singular does the same: l’ultima.
The plural of masculine nouns that start with a vowel sound uses gli: gli ultimi treni (not i ultimi treni).

Why does ultimo come before treno? Don’t adjectives usually follow the noun?

Most descriptive adjectives come after the noun, but several types typically come before it:

Ordinals and related ideas like primo, secondo, ultimo
Quantity, evaluation, and common short adjectives (e.g., bello, bravo, caro in some meanings) So l’ultimo treno is the normal, neutral order. Il treno ultimo would sound poetic or marked.

Does ultimo agree with the noun? What are the other forms?

Yes, it agrees in gender and number with the noun:

Masculine: ultimo / ultimi (l’ultimo treno, gli ultimi treni)
Feminine: ultima / ultime (l’ultima corsa, le ultime corse)

Does ultimo mean “last” or “latest”?

Both, depending on context:

Last in a sequence: l’ultimo treno = the final train of the day/lineup.
Most recent: le ultime notizie = the latest news.
Context clarifies which sense is intended.

Why è in ritardo? What does the preposition in do here?

Essere in ritardo is a fixed expression meaning “to be late/delayed,” literally “to be in a state of delay.”

Other fixed pairs: essere in anticipo (to be early), essere in orario (to be on time).
You’ll also hear the more formal con ritardo in announcements: arrivare con ritardo.

How do I say by how much the train is late?

Use di + amount or a noun phrase with ritardo:

È in ritardo di 10 minuti.
Ha un ritardo di 10 minuti.
Arriverà con 10 minuti di ritardo.

Can I say Il treno è tardi?

No.

È tardi is an impersonal phrase meaning “it’s late” (time of day).
For people or things that are late relative to a schedule, use essere in ritardo: Il treno è in ritardo.
For yourself: Sono in ritardo (“I’m running late”).

Why essere and not stare (e.g., sta in ritardo)?

Because essere in ritardo is the idiomatic collocation. Stare in ritardo sounds wrong. Use stare for other constructions like stare per + infinitive (to be about to do something).

Can I use a verb instead of the set phrase? Like Il treno ritarda?

Yes, there are verb alternatives:

Il treno ritarda. (The train is running late.)
Il treno è stato ritardato. (The train has been delayed.)
Lo sciopero ha ritardato il treno. (The strike delayed the train.)
Note: ritardato used of people is offensive; use it only in neutral contexts like trains.

What’s the difference between È in ritardo and Arriverà in ritardo or Sarà in ritardo?

È in ritardo: a current state (it’s late now, relative to schedule).
Arriverà in ritardo: a future outcome (it will arrive late).
Sarà in ritardo: often expresses supposition/guess (“it’s probably late”), besides literal future.

Can I drop the article and say Ultimo treno è in ritardo?

No, not in normal Italian. Definite nouns almost always take the article: L’ultimo treno è in ritardo.
Dropping articles can appear in headlines or telegraphic styles only.

How do I make it plural?

Gli ultimi treni sono in ritardo.
Use gli because ultimi starts with a vowel sound; with no preceding adjective you’d say i treni (but here the adjective forces gli).

What’s the opposite of in ritardo?

In orario: on time.
In anticipo: early.
As an adjective: puntuale (punctual) — e.g., Il treno è puntuale.

Any pitfalls with spelling and accents in è and L’?

È/è (with grave accent) means “is.” E without accent is “and.”
At the start of a sentence, use uppercase È; if you can’t type it, Italians sometimes type E’ as a fallback, but È is preferred.
L’ is the elided article; keep the apostrophe attached: L’ultimo.

Pronunciation tips?

L’ultimo: stress on the first syllable UL-ti-mo.
treno: TRE-no, clear open vowels.
è: short open “eh.”
ritardo: ri-TAR-do, flip the Italian r; the stress is on TAR.
Link smoothly across the elision: Lul-ti-mo.