How to say "surprisingly" in Japanese

• ずいぶんJLPT N4approx.Common
  adverb (with と)Mainly a degree adverb meaning 'very, quite, considerably'; its 'surprisingly' side is mild, fitting remarks that something is, or has become, more than expected.
  私わたしたちはもうずいぶん長ながくここにいます。↗

  We've been here long enough.
• 案外あんがいJLPT N2approx.Common
  adverb (with と)The closest fit for 'unexpectedly, surprisingly': use it when an outcome differs from what you assumed — surprisingly easy, cheap or quick, for instance.
  ピクニックは案外あんがいつまらなかった。↗

  The picnic was a disappointment.
• 驚くほどおどろくほどCommon
  expression, adverbFocuses on degree: use it when something is astonishingly or remarkably extreme, the surprise lying in how great the extent is rather than in expectation being defied.
• よくもCommon
  adverbRarely the neutral 'surprisingly' you want: it typically introduces an indignant or reproachful exclamation — 'how dare you', 'you have the nerve' — surprise mixed with blame.

Choose 案外 when an outcome defies expectation, 「驚くほど」 when the degree itself astonishes, 「ずいぶん」 chiefly as a degree word 'quite/very' with only mild surprise, and 「よくも」 for indignant 'how dare' exclamations.

Usage comparisons are AI-assisted and cross-checked by multiple models; for study reference only

• ずいぶんvery
• 案外あんがいunexpectedly
• 驚くほどおどろくほどto a surprising degree
• 思いのほかおもいのほかunexpectedly
• 驚いたことにおどろいたことにsurprisingly
• びっくりするほどsurprisingly
• 思いがけずおもいがけずunexpectedly
• なかなかどうしてconsiderably (beyond one's expectations)
• なんとsurprisingly
• よくもsurprisingly
• 結構けっこうrather