Me falta un dato para terminar el informe.

Because faltar is being used in the sense of to be lacking / to be missing to someone, not to fail to do something.

In this sentence:

• me = to me / for me
• falta = is missing / is lacking

So me falta un dato literally works like:

• One piece of information is missing for me

That sounds unusual in English, but it is a very normal Spanish structure.

Compare:

• Me falta un dato. = I’m missing one piece of information.
• Falto yo. = I am absent / I’m the one missing.

So yo falto would mean I am missing/absent, which is a completely different idea.

Because the subject of the verb is un dato, which is singular.

Spanish faltar works a bit like gustar in terms of structure:

• Me falta un dato. = One piece of information is missing to me.
• Me faltan dos datos. = Two pieces of information are missing to me.

So the verb agrees with the thing that is missing, not with me.

Examples:

• Me falta tiempo. = I’m short of time.
• Me faltan cinco euros. = I’m five euros short.
• Me falta una firma. = I’m missing one signature.

Here me is an indirect object pronoun meaning to me or for me.

It shows who is affected by the lack.

So:

• Me falta un dato. = A piece of information is missing for me / I’m missing a piece of information.
• Te falta un dato. = You’re missing a piece of information.
• Le falta un dato. = He/she is missing a piece of information.

This pronoun is essential in this kind of sentence because it tells us who lacks the thing.

Both are possible, but they are not exactly the same in nuance.

• Necesito un dato para terminar el informe. = I need one piece of information to finish the report.
• Me falta un dato para terminar el informe. = I’m missing one piece of information to finish the report.

The second version emphasizes that:

• you already have most of what you need,
• but one item is still missing.

So me falta often sounds more specific and situational than necesito.

Dato means piece of information, fact, or data point, depending on context.

In this sentence, un dato is best understood as:

• a piece of information
• one fact
• one bit of data

Although English has the word data, in natural English we often translate un dato as a piece of information rather than a data (which is not standard English).

Examples:

• Necesito un dato más. = I need one more piece of information.
• Los datos están en la tabla. = The data are in the table / The data is in the table.

Because para + infinitive expresses purpose: in order to finish.

So:

• para terminar el informe = to finish the report / in order to finish the report

Use para when something is needed for a goal.

Examples:

• Necesito silencio para estudiar. = I need quiet to study.
• Me falta una firma para enviar el documento. = I’m missing a signature to send the document.

Por would not fit this meaning here. Por usually expresses ideas like because of, through, for the sake of, by, or during, depending on context.

Because el informe refers to a specific report, one that is already known in the context.

So the sentence implies something like:

• the report I’m working on
• the report we’ve been talking about

If you said un informe, it would sound more like a report, not a specific one.

Compare:

• Me falta un dato para terminar el informe. = I’m missing one piece of information to finish the report.
• Me falta un dato para terminar un informe. = I’m missing one piece of information to finish a report.

Both are grammatical, but el informe is more natural if both speakers know which report is meant.

Yes, and it changes the meaning slightly.

• Me falta un dato. = I’m missing one piece of information.
• Me falta un dato más. = I’m missing one more piece of information.

Más adds the idea that this is an additional missing item.

Examples:

• Me faltan dos páginas. = I’m missing two pages.
• Me faltan dos páginas más. = I’m missing two more pages.

Yes. Spanish allows some flexibility in word order.

The neutral order is:

• Me falta un dato para terminar el informe.

But you could also hear:

• Para terminar el informe, me falta un dato.

This version puts more focus on the purpose first: to finish the report.

You might also see:

• Un dato me falta para terminar el informe.

This is grammatical, but less neutral and more marked. It could sound literary, emphatic, or unusual in everyday speech.

So for normal conversation, the original order is the safest and most natural.

You can add a mí for emphasis, but you normally do not replace me with it.

Natural Spanish would be:

• A mí me falta un dato para terminar el informe.

Not:

• A mí falta un dato... ❌

The pronoun me is still needed. A mí is optional and adds emphasis or contrast.

For example:

• A Juan no le falta nada, pero a mí me falta un dato. = Juan isn’t missing anything, but I’m missing one piece of information.

Yes, very common. Using faltar this way is completely natural in Spain and across the Spanish-speaking world.

In Spain, you will often hear similar sentences such as:

• Me falta tiempo.
• Me faltan unos detalles.
• Te falta una firma.
• Nos falta un documento.

It is a standard, everyday way to say that something is still missing before a task can be completed.

Then the noun and the verb would usually both become plural.

Examples:

• Me faltan dos datos para terminar el informe. = I’m missing two pieces of information to finish the report.

• Me faltan varios datos para terminar el informe. = I’m missing several pieces of information to finish the report.

The pattern is:

• Me falta + singular noun
• Me faltan + plural noun

So the agreement depends on the missing thing, not on the person.

You can understand it literally, but you usually should not translate it that way in natural English.

Word-for-word:

• Me = to me
• falta = is lacking / is missing
• un dato = one piece of information
• para terminar el informe = to finish the report

So the literal structure is roughly:

• One piece of information is missing to me to finish the report

That helps explain the grammar, but it is not natural English. A better translation is:

• I’m missing one piece of information to finish the report.
• I still need one piece of information to finish the report.

So a literal translation is useful for understanding the Spanish grammar, but not for producing good English.