Me he equivocado.

Because the verb is equivocarse, which is a pronominal/reflexive verb in Spanish.

In dictionary form, it is:

• equivocarse = to make a mistake / to be mistaken

So when you say I made a mistake, you need the reflexive pronoun:

• me = myself
• he equivocado = have mistaken
• me he equivocado = I have made a mistake / I was mistaken

Even though English does not say I have mistaken myself here, Spanish uses the reflexive structure naturally.

No. In Me he equivocado, he is not the English pronoun he.

It is the 1st person singular present tense of haber, the auxiliary verb used to form compound tenses:

• he = I have
• has = you have
• ha = he/she has
• hemos = we have
• habéis = you all have
• han = they have

So:

• me he equivocado = I have made a mistake

With a conjugated verb, object/reflexive pronouns usually go before the conjugated verb in Spanish.

So the normal order is:

• me he equivocado
• te has equivocado
• se ha equivocado

Not:

• he me equivocado ❌

A useful rule:

• If the verb is conjugated, the pronoun normally goes before it.
• If the verb is an infinitive, gerund, or affirmative command, the pronoun can attach to the end.

Examples:

• Voy a equivocarme.
• Estoy equivocándome.
• Equivócate.

But in your sentence, he is conjugated, so me goes before it.

Because in this sentence equivocado is a past participle used with haber, and past participles used this way do not agree in gender or number with the subject.

So both a man and a woman say:

• Me he equivocado.

The participle stays the same.

Compare that with estar + equivocado, where it works more like an adjective and does agree:

• Estoy equivocado. (male speaker)
• Estoy equivocada. (female speaker)

So:

• Me he equivocado. = same for everyone
• Estoy equivocado/equivocada. = changes with gender

It is the present perfect:
haber (present tense) + past participle

Structure:

• me = reflexive pronoun
• he = have
• equivocado = made a mistake / mistaken

So grammatically it is the same kind of tense as English I have made a mistake.

In Spain, this tense is very common for actions connected to the present, especially:

• something that happened recently
• something within a time period that is still considered current

For example:

• Esta mañana me he equivocado.
• Hoy me he equivocado dos veces.

Both can often be translated as I made a mistake, but the nuance is different.

• Me he equivocado = present perfect
• Me equivoqué = preterite / simple past

In Spain, speakers often prefer me he equivocado when the mistake feels connected to now or to a current time frame.

Examples:

• Lo siento, me he equivocado.
  = Sorry, I’ve made a mistake.

• Ayer me equivoqué.
  = Yesterday I made a mistake.

A very general Spain Spanish tendency:

• today / this morning / recently / just now → often present perfect
• yesterday / last week / in 2020 → often preterite

But in some regions and in much of Latin America, the preterite may be used more often where Spain Spanish prefers the present perfect.

No, not if you mean I made a mistake.

The verb you need is equivocarse, so the pronoun is part of the normal structure:

• Me he equivocado. ✅
• He equivocado. ❌

Without me, it sounds incomplete or wrong for this meaning.

Yes, you can, but you usually do not need to.

Spanish often leaves out subject pronouns because the verb ending already shows who the subject is:

• Me he equivocado. = perfectly normal
• Yo me he equivocado. = also correct

Adding yo can give:

• emphasis
• contrast
• extra clarity

For example:

• Yo me he equivocado, no tú.
  = I made the mistake, not you.

So the version without yo is the default, and the version with yo is more emphatic.

Not exactly.

They are related, but they focus on slightly different things:

• equivocarse = to make a mistake / to be mistaken
• estar equivocado = to be wrong / to be mistaken

Examples:

• Me he equivocado.
  Focus: I made a mistake

• Estoy equivocado.
  Focus: I am wrong

Very often they are close in meaning, but the grammar is different:

• equivocarse = verb
• estar equivocado = estar + adjective

Also remember:

• Me he equivocado. → equivocado does not change for gender
• Estoy equivocado/equivocada. → it does change

Put no before the pronoun:

• No me he equivocado.
  = I haven’t made a mistake / I’m not mistaken

The order is:

• no + reflexive pronoun + auxiliary + participle

So:

• No me he equivocado
• No te has equivocado
• No se ha equivocado

You can simply raise your intonation in speech, or use question marks in writing:

• ¿Me he equivocado?
  = Have I made a mistake? / Am I mistaken?

Spanish does not usually need a word-order change like English does.
You do not invert the verb and subject the way English does.

So the statement and the question can have the same word order:

• Me he equivocado.
• ¿Me he equivocado?

The difference is mainly:

• intonation in speech
• question marks in writing

A simple pronunciation guide is:

• meh eh eh-kee-boh-KAH-doh

A few helpful points for Spain Spanish:

• me sounds like meh
• he is pronounced like a short eh; the h is silent
• v in equivocado is pronounced like a soft Spanish b
• the stress falls on -ca-: e-qui-vo-CA-do

In IPA (roughly, in standard Spain Spanish):

• [me e e.ki.βoˈka.ðo]

Also, in natural speech, me he may run together a bit smoothly, so it can sound quite fluid.

Yes, very natural.

Me he equivocado is commonly used when:

• admitting a mistake
• correcting yourself
• apologising
• acknowledging that you were wrong

Very common examples:

• Perdón, me he equivocado.
• Lo siento, me he equivocado.
• Ah, no, me he equivocado.

It is a normal, everyday sentence in Spain Spanish.