El dólar bajó hoy.

Bajó is the third-person singular preterite form of bajar, which usually means to go down, to fall, or to decrease.

In this sentence, El dólar bajó hoy, it means that the dollar fell/went down today.

So the basic breakdown is:

• bajar = to go down / to lower / to decrease
• bajó = he/she/it went down or fell

Here, it refers to el dólar.

Because bajó is in the preterite, which is a past tense.

• baja = it goes down / is going down (present tense, depending on context)
• bajó = it went down / fell (completed past action)

Since the sentence says today but refers to something that already happened, Spanish often uses the preterite to present it as a completed event.

The accent mark on bajó shows both pronunciation and meaning.

Compare:

• bajo = I go down / low / under (depending on context)
• bajó = he/she/it went down

So the accent helps distinguish the preterite form from other words or forms.

It also tells you the stress falls on the last syllable: ba-JÓ.

Dólar has a written accent because of Spanish stress rules.

Without the accent, Spanish pronunciation rules would tend to stress it differently. The accent shows the correct stress is on the first syllable:

• DÓ-lar

This is just the normal Spanish spelling of the word.

Spanish often uses the definite article more than English does.

Here, el dólar means the dollar and refers to the currency as a market or economic subject. In financial news or general statements, Spanish commonly uses the article with currencies, markets, commodities, and similar nouns.

So:

• El dólar bajó hoy = The dollar fell today

This sounds natural in Spanish.

Grammatically, Spanish often allows the subject to be omitted, but in this case it would usually sound too vague unless the context already made it completely clear what went down.

• El dólar bajó hoy = clear and self-contained
• Bajó hoy = It fell today, but what fell?

So yes, Spanish can omit subjects, but here the noun is included because it carries the key information.

Bajó is the preterite.

• bajó = simple past / preterite
• ha bajado = present perfect

In Spain Spanish, both can be possible with hoy, but they are not always used in exactly the same way.

Very roughly:

• El dólar bajó hoy presents the fall as a completed event.
• El dólar ha bajado hoy connects it more directly to today/the present moment.

In news-style language, bajó hoy is very common and natural.

Yes, hoy can move around.

All of these are possible:

• El dólar bajó hoy.
• Hoy bajó el dólar.
• El dólar hoy bajó. (possible, but less neutral)

The version in your sentence is very neutral and common. Putting hoy at the end often sounds natural when it is just adding the time information after the main statement.

A simple pronunciation guide is:

el DÓ-lar ba-JÓ oi

A few points:

• el sounds like ell, but shorter
• dólar = stress on DÓ
• bajó = stress on JÓ
• hoy sounds roughly like oi

In most of Spain, the j in bajó is a strong throaty sound, stronger than English h.

Not usually here. In this sentence, it is being used in an economic/figurative sense.

So El dólar bajó hoy means the dollar:

• fell in value
• went down on the market
• decreased

Spanish uses bajar very naturally for prices, currencies, temperatures, numbers, and similar things.

Yes. Cayó from caer can also mean fell, and it is common in financial contexts.

The difference is often one of style or nuance:

• bajó = went down / decreased
• cayó = fell

Both are natural. Bajó can sound slightly more general and straightforward, while cayó can sometimes sound a bit more dramatic, depending on context.

Yes. Dólar is masculine, which is why it takes el:

• el dólar
• un dólar

Its plural is:

• los dólares

So if you changed the subject, you would also change agreement where needed:

• Los dólares... if you were talking about dollars in general, though in this kind of market sentence, el dólar is the usual form.