Regningen skal betales i dag.

Because regningen is the definite form of regning.

• en regning = a bill
• regningen = the bill

Danish usually adds the definite article to the end of the noun instead of putting a separate word in front, as English does.

So:

• en bil = a car
• bilen = the car

Here, the sentence is talking about a specific bill, so Danish uses regningen.

Because the sentence is passive.

• skal betale would mean must pay
• skal betales means must be paid

In this sentence, the bill is not doing the action. The bill is receiving the action. That is why Danish uses the passive form betales.

Compare:

• Jeg skal betale regningen = I must pay the bill
• Regningen skal betales = The bill must be paid

Here, skal expresses necessity, obligation, or something that is required.

So in this sentence, it means something like:

• must
• has to
• is to

It does not mainly mean simple future here. Danish skal can sometimes point to the future, but in this sentence the important idea is obligation: the payment needs to happen today.

Yes. It is a passive sentence.

The active version would be something like:

• Nogen skal betale regningen i dag = Someone must pay the bill today

The passive version removes the person doing the action and focuses on the bill instead:

• Regningen skal betales i dag

This is very common in Danish, especially in formal, written, or practical contexts.

It is formed from the verb betale (to pay) plus the passive -s ending.

• betale = active infinitive
• betales = passive infinitive / passive form used after skal

This -s passive is a very common Danish pattern.

Examples:

• Døren åbnes = The door is opened / opens
• Bogen læses = The book is read
• Regningen skal betales = The bill must be paid

Danish can also form the passive with blive + past participle:

• Regningen skal blive betalt i dag

That is grammatically possible, but skal betales is usually more natural and more concise here.

Very roughly:

• -s passive often sounds more neutral, general, or official
• blive-passive can sound a bit more event-focused or explicit

In practical statements like bills, rules, instructions, and formal notices, skal betales is extremely common.

Because it is the subject of the passive sentence.

In English, the subject is also at the beginning in the passive:

• The bill must be paid today

The same happens in Danish:

• Regningen = subject
• skal = finite verb
• betales = passive verb form
• i dag = time expression

So the sentence structure is very normal.

The basic order is:

Subject + finite verb + infinitive/passive verb + time expression

So here:

• Regningen = subject
• skal = finite verb
• betales = infinitive/passive form
• i dag = time expression

A very literal breakdown is:

• Regningen = the bill
• skal = must
• betales = be paid
• i dag = today

Yes.

You can also say:

• I dag skal regningen betales

That means the same thing, but it puts more emphasis on today.

This is a very common Danish pattern: if you move something to the front, the finite verb still stays in second position.

So:

• Regningen skal betales i dag
• I dag skal regningen betales

Both are correct.

Yes, it is a very common time expression meaning today.

It is written as two words:

• i dag = today

Other similar time expressions are:

• i morgen = tomorrow
• i går = yesterday

So learners should usually memorize i dag as a set phrase.

A careful approximate pronunciation is:

rai-ning-en skal be-TA-lehs i dai

A few useful notes:

• regningen often sounds more like rai-ning-en than the spelling suggests
• skal has a broad a
• betales has stress on -ta-
• dag often sounds closer to dai in standard Danish pronunciation

As usual with Danish, the spoken form is often less clear and more reduced than the spelling suggests.

Sometimes in English translation, yes, depending on context. But grammatically, skal is usually stronger than English should.

The most direct idea is:

• must be paid today
• has to be paid today

If the context is softer, English might choose should, but the Danish word itself normally expresses a stronger requirement than that.

Yes, very much.

Regningen skal betales i dag sounds natural in:

• reminders
• notices
• instructions
• formal messages
• administrative language

The passive structure makes the sentence sound impersonal and practical, which is often exactly what Danish wants in this kind of context.