Another way to talk about the validity of something is to mention when it expires. This is simply another way to answer the question. I hope that this helps! :)
面接という状況であれば、「My visa expires on March 18, 2018」が最もスタンダードな言い方かと思います。友人とおしゃべりしているような状況でしたら「My visa is good until March 18, 2018」という言い方もできます。ご参考にしていただければ幸いです。
"Expires" means is no longer valid and can no longer be used. So, the day that your visa is valid until, is the same as the day that it expires.
"My visa doesn't expire until..." indicates that your visa is valid and operational up until the date of March 18, 2018.
"The expiry date" indicates that there is a specific date at which point your visa is no longer valid. After this "expiry date" your visa is "expired", is no longer valid, and needs to be renewed. The term expiry date can be used for things such as visas, food, drinks, policies, contracts, documents, etc. It is most often used in reference to food or legal documents.
"Expires" は「有効期限が切れる」という意味です。ですから、ビザの有効期限が切れる日は、ビザが "Expires" する日です。
"My visa doesn't expire until..." は、ビザが2018年3月18日まで有効であることを表します。
"The expiry date" は、ビザの有効期限が切れる特定の日付があることを表します。この "Expiry date" を過ぎるとビザは "Expired"（失効）するので再び更新しなければなりません。
"Expiry date" という言葉は、ビザ・食べ物・飲み物・政策・契約・文書などについて使えます。ほとんどの場合は、食べ物か法律文書に関して使われます。
Since 2018 is already over, I chose to phrase the first two answers as simply, "March 18," in case the speaker actually means that their visa expires this month in 2019. In English, it is important to note that, "until" means a condition that currently exists and will continue to exist until a certain point in time, rather than a condition that has not yet begun. However, if the speaker meant to say that their visa had already expired in 2018, the final sentence expresses this.
If asked about the validity of your visa, you can use any of the above-mentioned expressions: Subject(your visa) + Is + valid + until (followed by a date) OR Subject + "expires on" (proceeded by a date). The expression "expires on" changes to "expires in" when you are only referring to the month.
E.g., My visa expired in May, 1954
My visa will expire in March.
My visa expires on March 18, 2018
I hope this helps:)
ビザの効力について聞かれたときには、上記どちらの表現も使えます。
主語（My visa）+ Is + valid + until（日付が続く）
または
主語 + "expires on"（日付が続く）
「月」のみに言及するときには、"expires on" を "expires in" に変えます。
例：
My visa expired in May, 1954（私のビザは1954年5月に切れました）
My visa will expire in March.（私のビザは3月で切れます）
My visa expires on March 18, 2018（私のビザは2018年3月18日に切れます）
参考になれば幸いです。
When asked when your visa is valid until, and you want to explain that it is valid until March 18, 2018, you can use one of the abovementioned suggestions.
If the visa validity has already expired, the date is not actually important at all, so the third suggestion may be more appropriate
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