Learn Hardcore Swedish: Jag jobbar mycket under året.

jobbar comes from jobba and is more colloquial, common in everyday speech.
arbetar comes from arbeta and sounds a bit more formal or written.

You could say Jag arbetar mycket under året too; it’s correct but slightly more formal in tone.

Does Jag jobbar mean “I work” or “I’m working”? How is Swedish present tense used?

Swedish present tense usually covers both English simple present and present continuous.
Jag jobbar can mean:

“I work” (in general, as a habit)
“I’m working” (right now), if the context makes that clear

If you really want to stress “right now”, you can say Jag håller på att jobba or Jag jobbar just nu.

Why is it mycket and not många in Jag jobbar mycket?

In Swedish:

mycket is used with uncountable things or as an adverb (“a lot, much”).
många is used with countable nouns (“many”).

Here mycket describes how much you work (an adverb modifying jobbar), so mycket is correct.
You’d say, for example:

Jag har många jobb = I have many jobs.
Jag jobbar mycket = I work a lot.

Can I move mycket to another place in the sentence?

The neutral word order is Jag jobbar mycket under året.
Putting mycket right after the verb is the usual and most natural choice.

Other orders are possible but sound marked or odd in normal speech:

Jag jobbar under året mycket. – Grammatically possible but sounds unnatural.
Mycket jobbar jag under året. – Very unusual; could be poetic or very emphatic.

So, keep mycket directly after jobbar in this kind of sentence.

Why do we say under året and not i året or på året?

In time expressions, under is the normal preposition for “during / over the course of” a period.
So under året literally means “during the year / throughout the year”.

i året isn’t used in this sense.
på året appears in some fixed phrases like den varmaste dagen på året (“the warmest day of the year”), but not for “I work a lot during the year”.

For “during the year” as a general time span, under året is the idiomatic choice.

Why is it året (definite) and not just år?

År is “year” and året is “the year”. In expressions like under året, Swedish prefers the definite form.

Under året can mean:

“during the year” (this year, from context), or
“during the year” in a more general, typical-year sense (“over the course of a year”).

You would not say under år on its own. If you want to say “for a year” (one year as a duration), you’d say i ett år or under ett år, not under år.

Does under året mean this specific year, or any typical year?

It’s ambiguous and depends on context.

In many contexts, under året = “during the year (this year)”, especially if you’re talking about plans or the current calendar year.
It can also be understood more generally as “over the course of a (typical) year”, like a habitual statement: Jag jobbar mycket under året = “I work a lot over the course of a year (in general).”

Without extra context like i år (“this year”), both readings are possible.

Is there a difference between Jag jobbar mycket under året and Under året jobbar jag mycket?

Both sentences are grammatically correct and mean almost the same thing.

Jag jobbar mycket under året. – Neutral word order, focus on “I work a lot”.
Under året jobbar jag mycket. – Puts Under året (the time frame) first and gives it a bit more emphasis: “During the year, I work a lot.”

Swedish has the V2 rule (the verb is the second element), so when Under året comes first, jobbar must still be in second position: Under året [1] jobbar [2] jag [3] mycket.

Can I leave out jag, like in some other languages?

No. In Swedish, you almost always need the subject pronoun.
You can’t say Jobbar mycket under året as a normal, complete sentence.

So Jag jobbar mycket under året is required, just like English needs I in “I work a lot during the year.”

How do you pronounce Jag jobbar mycket under året?

Approximate pronunciation (standard Swedish):

Jag – often [ja] or [jɑː] in everyday speech (the g is usually very weak or silent).
jobbar – [ˈjɔbːar]; double b means a longer b sound.
mycket – [ˈmʏkːɛt]; y is a front rounded vowel (between “i” and “u”), and ck gives a long k.
under – [ˈɵndɛr]; the u here is [ʉ]/[ɵ], also a front rounded vowel.
året – [ˈoːrɛt]; long å like the “o” in “more”, and final -et is a short [ɛt].

Spoken quickly, the sentence flows together roughly as: [ja ˈjɔbːar ˈmʏkːɛt ˈɵndɛr ˈoːrɛt].

Does under året mean “for a whole year, continuously”?

Not necessarily. Under året describes the time frame, not that the action is continuous.

Jag jobbar mycket under året means that, over the course of the year, in total, you work a lot (for example, many hours, many periods of work).
If you want to stress continuous duration, you’d use something like:

Jag har jobbat i ett år. – I have worked for a year.
Jag jobbade under ett helt år. – I worked for a whole year.

How would I say the negative: “I don’t work much during the year”?

You place inte (not) after the verb, before mycket:

Jag jobbar inte mycket under året.
= “I don’t work much during the year.”

Word order pattern:

Jag (subject)
jobbar (verb)
inte (negation)
mycket (adverb)
under året (time expression).

Could I say Jag arbetar mycket under året instead? Does it sound strange?

You can absolutely say Jag arbetar mycket under året. It’s grammatically correct.

Compared to Jag jobbar mycket under året:

arbetar sounds a bit more formal or neutral, and is common in written language, reports, or formal speech.
jobbar sounds a bit more casual/spoken, typical in everyday conversation.

Both are fine; choice of verb is mostly about style and register.