Obrigado.

This depends on the speaker’s gender, not the gender of the person being thanked.

• A man usually says obrigado
• A woman usually says obrigada

That is because obrigado/obrigada originally behaves like an adjective meaning something like obliged or thankful.

So:

• If you are male: Obrigado
• If you are female: Obrigada

Yes. Obrigado. is a complete, natural sentence in Brazilian Portuguese.

It is very commonly used on its own in everyday situations, just like saying Thanks. in English.

You can also make it longer if you want:

• Muito obrigado. = Thank you very much.
• Obrigado mesmo. = Thanks a lot / Really thank you.
• Obrigado pela ajuda. = Thanks for the help.

In Brazilian Portuguese, obrigado is commonly pronounced approximately like:

oh-bree-GAH-doo

A more accurate rough guide is:

• o = like o in off or a short oh
• bri = bree
• ga = GAH (this is the stressed part)
• do = a light doo

Stress: obriGAdo

In IPA, a common Brazilian pronunciation is /obɾiˈɡadu/.

A few details:

• The r here is a tapped sound, a quick flap, somewhat like the tt in American English butter
• The final o in Brazil often sounds like u, which is why it may sound like obrigadu

It is neutral and works in both formal and informal situations.

You can use obrigado/obrigada:

• with friends
• in shops
• with coworkers
• with strangers
• in polite conversation

If you want to sound warmer or more emphatic, you can add words:

• Muito obrigado.
• Obrigadão. (more informal, friendly, stronger)
• Obrigado mesmo.

So obrigado is a safe default in almost any situation.

Historically, obrigado/obrigada comes from the idea of being obliged or indebted to someone.

So when you say Obrigado, the underlying sense is something like:

• I am obliged to you
• I’m thankful
• Much obliged

That is why the word changes for the speaker’s gender: it acts like an adjective describing the person speaking.

Yes. Obrigado/obrigada works whether you are thanking:

• one person
• several people
• a group
• an organization

The form usually still agrees with the speaker, not with the people being thanked.

Examples:

• A man thanking one person: Obrigado
• A man thanking a group: Obrigado
• A woman thanking one person: Obrigada
• A woman thanking a group: Obrigada

If a group is speaking together, you may also hear plural forms:

• Obrigados = spoken by a group of men or a mixed group
• Obrigadas = spoken by a group of women

But for one speaker, just use singular obrigado or obrigada.

Yes. In casual speech, many Brazilians say:

• brigado = informal short form of obrigado
• brigada = informal short form of obrigada

This is common in speech and texting, but learners should first get comfortable with the full form obrigado/obrigada, since it is standard and always appropriate.

Yes. Both can express thanks, but the tone is different.

• Obrigado/obrigada = standard, neutral, polite
• Valeu = informal, casual, friendly

Use obrigado/obrigada in most situations, especially if you are unsure. Use valeu more with friends or in relaxed everyday conversation.

So if you want the safest option, choose obrigado/obrigada.

No. Normally you do not say eu here.

Just say:

• Obrigado.
• Obrigada.

Portuguese often leaves out the subject when it is already understood, and in this expression the subject is naturally I.

Saying Eu estou obrigado would not be the normal way to say thank you. The set expression is simply Obrigado/Obrigada.