Jag har ont i fingret idag.

Because ha ont is a fixed Swedish expression meaning to be in pain or to have pain.

• jag har ont = I am in pain / something hurts
• Swedish uses har (have), not är (am/is/are), in this expression.

So even though natural English often says my finger hurts, Swedish commonly expresses it as I have pain in the finger.

Ont means painfully, in pain, or hurting in this kind of sentence.

In jag har ont, it does not work like a regular noun such as pain. It is part of the expression ha ont.

You will often see:

• Jag har ont. = I’m in pain.
• Jag har ont i ryggen. = My back hurts.
• Har du ont? = Are you in pain?

So it is best to learn ha ont as one whole phrase.

Here i means in or in the area of, but in English we usually translate it more naturally as in my finger or simply my finger hurts.

Swedish often uses ha ont i + body part:

• ha ont i huvudet = have a headache / have pain in the head
• ha ont i ryggen = have pain in the back
• ha ont i fingret = have pain in the finger

So i is the normal preposition with body parts in this pattern.

Swedish very often uses the definite form of body parts where English uses a possessive.

So:

• Jag har ont i fingret literally looks like I have pain in the finger
• but it naturally means My finger hurts or I have pain in my finger

This is very common with body parts:

• Jag tvättar händerna. = I wash my hands.
• Hon bröt benet. = She broke her leg.
• Han har ont i magen. = His stomach hurts.

You can sometimes use a possessive like mitt finger, but in ordinary Swedish, the definite form is usually more natural here.

Because the noun is ett finger.

For many ett nouns, the definite singular ending is -et:

• ett finger = a finger
• fingret = the finger

So the forms are:

• indefinite singular: ett finger
• definite singular: fingret
• indefinite plural: fingrar
• definite plural: fingrarna

No, idag is not required. It just adds the meaning today.

• Jag har ont i fingret. = My finger hurts.
• Jag har ont i fingret idag. = My finger hurts today.

Its position is natural at the end, but Swedish can move time expressions around for emphasis:

• Jag har ont i fingret idag.
• Idag har jag ont i fingret.

Both are correct, but the first one is a very neutral everyday word order.

Yes, it is very natural.

A native speaker would commonly say:

• Jag har ont i fingret idag.

Depending on context, other natural sentences are also possible, such as:

• Mitt finger gör ont idag. = My finger hurts today.

But jag har ont i fingret idag is extremely standard and common.

Both are natural, but they focus slightly differently.

• Jag har ont i fingret = I have pain in my finger
• Mitt finger gör ont = My finger hurts

The first is often the more common everyday pattern when talking about pain in a body part. The second is also completely normal and may feel a little more directly focused on the finger itself.

So for a learner, ha ont i + body part is a very useful pattern to remember.

A rough guide for an English speaker:

• jag sounds roughly like yah in many casual accents, though careful speech can sound more like yag
• har sounds like har
• ont sounds roughly like ohnt
• i sounds like ee
• fingret sounds roughly like FING-ret
• idag sounds roughly like ee-DAHG

A very rough full pronunciation could be:

yah har ohnt ee FING-ret ee-DAHG

A few important notes:

• The g in jag is often weak or disappears in everyday speech.
• Swedish vowel length and pitch accent matter, so an exact pronunciation is hard to show in English spelling.
• The stress in idag is on the second syllable: i-DAG.

Yes — very often. This is one of the most useful Swedish patterns for talking about pain.

Examples:

• Jag har ont i huvudet. = I have a headache.
• Jag har ont i ryggen. = My back hurts.
• Jag har ont i magen. = My stomach hurts.
• Jag har ont i benet. = My leg hurts.
• Jag har ont i handen. = My hand hurts.

So ha ont i + definite body part is a pattern worth memorizing.

Then you would usually use the plural definite form:

• Jag har ont i fingrarna idag. = My fingers hurt today.

Here:

• fingrar = fingers
• fingrarna = the fingers

Again, Swedish uses the definite form of the body part rather than a possessive in many cases.