In short

V-た + ことがあります is the English present perfect “I have (ever) done X” - an experience you carry, at some unspecified point in your life. It is literally an existence sentence: “an occasion of having done X exists.” Use it for the rare and the memorable, never for what you did yesterday.

The rule

Step 1 - Take the plain た-form and hang ことがあります on it.

The pattern is V-た + こと + が + あります. The verb inside is plain, from lesson 17; the politeness of the whole sentence is carried once, at the end, by あります. This is the register point that trips everyone: ×行きましたことがあります is wrong, 行ったことがあります is right.

• 行く iku -> 行った -> 行ったことがあります itta koto ga arimasu (I have been)
• 食べる taberu -> 食べた -> 食べたことがあります tabeta koto ga arimasu (I have eaten)

こと is the nominalizer from lesson 26: it turns the whole clause 日本へ行った into a noun, “the fact of having gone to Japan.” That noun is then the subject of ある, which is why the particle is が and why the verb is あります (こと is abstract, so never います). Note that this is one place where the other nominalizer の cannot be substituted: ×日本へ行ったのがあります is not Japanese - this pattern is fixed with こと.

Step 2 - Negative and question.

Only the final あります moves. Everything to its left is frozen.

• Negative: 〜たことがありません ta koto ga arimasen (I have never…) - the plain equivalent is 〜たことがない.
• Question: 〜たことがありますか ta koto ga arimasu ka (Have you ever…?)

Step 3 - Know what does not count as an experience.

This is the real difficulty, and it is a meaning problem, not a form problem. Compare:

• 日本へ行ったことがあります。 - experience, floating free of any date: I have been to Japan (at some point).
• 去年日本へ行きました。 - a specific, dated event: I went to Japan last year.

So 〜たことがある is banned in three situations, where the plain past is the only option:

1. Recent events. ×昨日すしを食べたことがあります -> 昨日すしを食べました。
2. Specific, located events. Once you say 去年, 先月 or 先週, you are reporting an occurrence, not an experience.
3. Expected or everyday events. ×ご飯を食べたことがあります is odd, because eating is not a rare achievement. The pattern needs the event to have some novelty value - somewhere you went, something unusual you tried, something that happened once and stuck.

A useful gate: if English would sound strange with “ever” in it, Japanese will sound strange with 〜たことがある.

Step 4 - Counting experiences: switch to 〜ている.

Adding a count to 〜たことがある is fine when you are still measuring rarity (二回あります). But when the event is repeatable and the running total is what matters, 〜ています from lesson 15 is the other option, presenting the count as a standing record (三回読んだことがあります stays available too):

• この本はもう三回読んでいます。 Kono hon wa mō sankai yonde imasu. - I have already read this book three times.

The difference: 読んだことがあります files the book away as a past experience; 読んでいます presents a record that is still open and could grow.

Step 5 - Answering the question.

Answers strip the sentence back to あります／ありません, because the こと clause is already understood.

• はい、あります。 Hai, arimasu. - or with a count, はい、二回あります。
• いいえ、ありません。 Iie, arimasen. - or, emphatically, いいえ、一度もありません。 Iie, ichido mo arimasen. (No, not even once.)

一度も ichido mo (“not even once”) is the standard intensifier and requires a negative predicate.

Step 6 - A different pattern that looks identical: dictionary form + ことがある.

Swap the た-form for the dictionary form and the meaning changes completely: V-plain non-past + ことがあります = it sometimes happens that…, an occasional occurrence rather than a life experience.

• この電車はたまに遅れることがあります。 Kono densha wa tama ni okureru koto ga arimasu. - This train is sometimes delayed.

It belongs to a later stage and is not what this lesson drills - but you must be able to tell the two apart on sight, because the only difference is the た-form versus the dictionary form. The table below sets them side by side; everything else here is the た-form sense.

Forms & patterns

Building it, by verb class (the た-form is the て-form with て -> た, で -> だ):

The four cells - only あります changes:

Three ways to talk about the past - keep them apart:

Words that live with this pattern:

Examples

Common mistakes

• 昨日すしを食べたことがあります。 (Kinō sushi o tabeta koto ga arimasu.) -> 昨日すしを食べました。 (Kinō sushi o tabemashita.) - a dated, recent event is a plain past report. 〜たことがある needs an unspecified point in a life.
• 日本へ行きましたことがあります。 (Nihon e ikimashita koto ga arimasu.) -> 日本へ行ったことがあります。 (Nihon e itta koto ga arimasu.) - the verb before こと must be plain. Politeness is marked once, by あります at the end.
• 日本へ行くことがあります。 (Nihon e iku koto ga arimasu.) -> 日本へ行ったことがあります。 (Nihon e itta koto ga arimasu.) - the dictionary form gives “I sometimes go to Japan.” Experience requires the た-form.
• 一度もすしを食べたことがあります。 (Ichido mo sushi o tabeta koto ga arimasu.) -> 一度もすしを食べたことがありません。 (Ichido mo sushi o tabeta koto ga arimasen.) - 一度も can only end in a negative; with an affirmative it is a contradiction.
• 富士山に登ったことをあります。 (Fujisan ni nobotta koto o arimasu.) -> 富士山に登ったことがあります。 (Fujisan ni nobotta koto ga arimasu.) - ある is an existence verb, not a transitive one; the nominalized こと is its subject, so it takes が.

Tips

• Test it with the English word “ever.” Have you ever climbed Mount Fuji? -> 〜たことがありますか. Did you climb it last summer? has no “ever” in it, so it is a plain past. This one test kills the most common error in the whole lesson.
• Read it literally and the particles stop being arbitrary: 日本へ行ったことがあります = “the-having-gone-to-Japan exists.” こと is a noun, ある is its verb, が is the subject marker. Nothing here is idiomatic.
• In questions and negatives you will often hear は instead of が - 行ったことはありますか - which sets the experience up as the topic under discussion (“as for ever going…”). Both are correct; が is the safe default while you are learning.
• Casual speech drops the が entirely: 日本、行ったことある？ Nihon, itta koto aru? Keep あります in polite conversation, but expect the bare 〜たことある from friends.