Ég giska á að hún komi seint.

Giska á means to guess, to estimate, or to make a prediction about.

In this sentence, Ég giska á að... is basically I guess that... or My guess is that...

A useful thing to remember is that giska normally appears with á in this meaning, so you learn it best as a unit: giska á.

They do different jobs:

• á belongs to the expression giska á
• að introduces the subordinate clause, meaning that

So the structure is:

Ég giska á + að hún komi seint

In other words:

• giska á = guess
• að hún komi seint = that she will/is likely to come late

This is not the infinitive marker að. Here it is a conjunction meaning that, because it is followed by a finite verb: komi.

Because Icelandic normally uses the subjunctive after expressions like guess, think, suppose, or other statements that involve uncertainty, opinion, or indirect reporting.

So:

• hún kemur seint = she comes / is coming late or she will come late as a more direct statement
• Ég giska á að hún komi seint = I guess that she’ll come late, where the coming is presented as uncertain

So komi is the expected form in standard Icelandic here.

Komi is the present subjunctive of koma (to come).

Here is the contrast:

• infinitive: koma
• present indicative: kemur = comes / is coming
• present subjunctive: komi

In this sentence, the subjunctive is used because the speaker is making a guess, not stating a confirmed fact.

Because Icelandic present forms often cover both present and future meaning, depending on context.

So að hún komi seint can mean something like:

• that she is coming late
• that she will come late

In English, I guess she’ll come late often sounds more natural, but Icelandic does not need a separate future form here.

Because this is a normal subordinate clause introduced by að.

The usual order is:

að + subject + verb + adverb

So:

• að = that
• hún = she
• komi = come
• seint = late

That gives:

að hún komi seint

This is the standard, neutral word order.

Seint is the adverb late.

Compare:

• seinn = late as an adjective, used to describe a noun
• seint = late as an adverb, used to describe a verb or action

Here it describes how she comes, so Icelandic uses the adverb:

• hún kemur seint = she comes late

If you were describing a noun, you would use an adjective form instead, for example:

• hún er sein = she is late

Hún is the nominative form of she, because it is the subject of komi.

In the clause að hún komi seint, the person doing the action of coming is she, so nominative is required.

Yes. That would be very natural.

• Ég giska á að hún komi seint = I guess she’ll come late
• Ég held að hún komi seint = I think she’ll come late

The difference is mainly nuance:

• giska á feels more like a guess or estimate
• halda in ég held að... feels more like I think...

Both commonly take a subordinate clause with að and often the subjunctive.

You usually put ekki after the finite verb in the subordinate clause:

Ég giska á að hún komi ekki seint.

That means I guess she won’t come late or I guess she isn’t coming late.

So the order is:

að hún komi ekki seint

You can also negate the main clause instead, depending on meaning:

Ég giska ekki á að hún komi seint.

That means something more like I don’t guess / I’m not guessing that she’ll come late, which is less common and has a different focus.

A common past version is:

Ég giskaði á að hún kæmi seint.

That means I guessed that she would come late or I guessed she was coming late.

Notice the changes:

• giska → giskaði for the past tense in the main clause
• komi → kæmi, the past subjunctive of koma

So the mood stays similar, but the tense shifts back.

It can definitely be used in everyday speech. It is natural and understandable.

That said, in very casual conversation, speakers may often choose other verbs too, such as:

• Ég held að... = I think that...
• Ég býst við að... = I expect that...
• Kannski kemur hún seint. = Maybe she’ll come late.

So Ég giska á að hún komi seint is perfectly good Icelandic, but depending on tone and context, another phrasing may sound more common.

Yes — three things are especially useful:

1. Learn giska á as a set expression.
   Not just giska, but giska á.

2. Notice að introducing a clause.
   Here it means that, not to.

3. Pay attention to the subjunctive komi.
   This is a very common pattern after verbs of guessing, thinking, or uncertainty.

So this sentence is a great example of a bigger pattern:

main clause of opinion/guess + að + subjunctive clause