Die Hausverwaltung hat geschrieben, dass die Mieterhöhung ab nächstem Monat gilt.

Hat geschrieben is the Perfekt tense, which is very commonly used in spoken German and also often in everyday written German.

• hat geschrieben = has written / wrote
• schrieb = simple past (Präteritum)

In many contexts, especially with most full verbs, German prefers Perfekt where English might simply use the past tense.

So this sentence uses a very normal everyday pattern:

• Die Hausverwaltung hat geschrieben ...

If you changed it to Die Hausverwaltung schrieb ..., it would still be grammatical, but it sounds a bit more literary, formal, or narrative.

Hausverwaltung is a compound noun:

• Haus = house/building
• Verwaltung = administration/management

Together, Hausverwaltung usually means the property management company or building management responsible for an apartment building or rental property.

So it does not usually mean a single person. It often refers to the office or organization that handles things like:

• rent matters
• repairs
• notices to tenants
• contracts
• service charges

In German, a clause introduced by dass is a subordinate clause, and subordinate clauses are separated from the main clause by a comma.

So here:

• Die Hausverwaltung hat geschrieben,
• dass die Mieterhöhung ab nächstem Monat gilt.

This is standard German punctuation. Unlike English, where commas before that are often omitted, German requires the comma here.

Because dass introduces a subordinate clause, and in German subordinate clauses the conjugated verb goes to the end.

Compare:

• Main clause: Die Mieterhöhung gilt ab nächstem Monat.
• Subordinate clause: ..., dass die Mieterhöhung ab nächstem Monat gilt.

So the word order changes because of dass.

This is one of the most important German sentence patterns to learn:

• main clause → verb usually in second position
• subordinate clause → verb at the end

German often combines nouns into one long compound noun.

Mieterhöhung breaks down as:

• Miete = rent
• Erhöhung = increase

Together it means rent increase.

German normally writes this as one word, not two. That is very typical for German compound nouns.

A useful rule: When English often uses noun + noun combinations written separately, German often writes them as one compound noun.

Here, ab means starting from. In this time expression, German uses the dative, which is why you get nächstem Monat.

You can think of it as a shortened form of:

• ab dem nächsten Monat

When the article is omitted, the adjective still shows the case ending:

• dem nächsten Monat → full form
• nächstem Monat → shortened form

So:

• ab nächstem Monat = from next month onward
• ab dem nächsten Monat = also correct, just a bit fuller

Why -em?

• Monat is masculine: der Monat
• after dative masculine with this kind of adjective ending, you get nächstem

So nächstem Monat is dative masculine singular.

Here ab means from or starting from in a time sense.

So ab nächstem Monat means something like:

• starting next month
• from next month onward

This is a very common use of ab with time expressions:

• ab morgen = starting tomorrow
• ab Montag = starting Monday
• ab nächster Woche / ab nächster Woche an = starting next week

It marks the point in time when something begins to apply.

German often uses the verb gelten to mean:

• to be valid
• to apply
• to be in force

So die Mieterhöhung gilt means the rent increase applies / is valid / takes effect.

That is a very natural choice in administrative or legal-style German.

You could sometimes say ist gültig, but that often sounds more like something officially valid as a document, ticket, pass, rule, etc. For a policy, rule, or increase taking effect, gelten is especially idiomatic.

So:

• Die Mieterhöhung gilt ab nächstem Monat. = very natural
• Die Mieterhöhung ist ab nächstem Monat gültig. = possible, but less standard in this context

Because in German, all nouns are capitalized.

So here:

• die Hausverwaltung
• die Mieterhöhung
• der Monat

all begin with capital letters because they are nouns.

This is one of the most noticeable differences from English. Adjectives and verbs are not capitalized unless they start the sentence, but nouns always are.

Both nouns are feminine singular:

• die Hausverwaltung
• die Mieterhöhung

So grammatically, they both take die in the nominative singular.

In this sentence:

• Die Hausverwaltung is the subject of hat geschrieben
• die Mieterhöhung is the subject of gilt inside the subordinate clause

The article also suggests that these are specific, known things in context:

• the building management responsible for this property
• the rent increase being discussed

So die here is both grammatically required and contextually natural.

Yes, absolutely. That is also correct.

Compare:

• ab nächstem Monat
• ab dem nächsten Monat

Both mean the same thing here. The shorter version without the article is very common in everyday German, especially in time expressions.

The version with dem can feel a little more explicit or slightly more formal, but both are standard.