Mistakingly or Mistakenly: Which Word Is Correct in US English?

Mistakingly and mistakenly look like twins, and both can sound “possible” if you say them quickly. But in everyday U.S. English, one choice is far safer and far more natural: mistakenly. Major dictionaries define mistakenly as “wrongly” or “by mistake.”

Mistakingly does exist (it appears in major references), but it is uncommon enough that many readers will pause, doubt it, or assume it is an error.

This guide explains what each word means, how each one reads, and what to use in U.S. writing today.

Quick Answer

Use mistakenly in standard U.S. English.

Mistakingly is recorded in reference works, but it is rare in modern writing and can look nonstandard to many readers.

Fast Rule

• If you mean “by mistake” or “wrongly,” choose mistakenly.
• If you want the sentence to sound smooth and natural in U.S. English, mistakenly is the default.

Why People Confuse Them

Both words are built around the idea of a mistake, so both feel “logical.” English also creates lots of adverbs with -ly (carefully, quietly, clearly), which makes mistakingly look believable at a glance.

But English does not always reward the “it looks logical” approach. Standard usage favors the form readers recognize instantly: mistakenly.

Key Differences At A Glance

• Meaning:
  • mistakenly = wrongly; by mistake
  • mistakingly = “in a mistaking manner” (rare/marked)
• Tone:
  • mistakenly feels normal and professional
  • mistakingly often feels unusual or distracts readers
• Best For School And Work:
  • Choose mistakenly

What “Mistakenly” Means

Mistakenly is the standard adverb for something done in error—either an action you did wrong or a belief you held that turned out to be wrong.

Common Meanings

• By mistake / unintentionally: “I mistakenly attached the older file.”
• Wrongly believed: “He mistakenly believed the meeting was at 3.”

What “Mistakingly” Means

Mistakingly is also listed in reference sources, including Merriam-Webster and the Oxford English Dictionary.

That said, the definition is narrow and the word is uncommon enough that it can read like a typo to many U.S. readers. If your goal is clean, modern U.S. writing, you usually lose nothing by choosing mistakenly instead.

Which One Is Correct In US English?

For standard U.S. English, mistakenly is the correct, expected, and safest choice.

Mistakingly may be “real,” but most writers do not need it, and many editors will replace it with mistakenly to avoid distracting the reader.

Mistakenly Vs Accidentally

These two words overlap, but they are not always interchangeable.

• mistakenly often implies a wrong belief, wrong judgment, or wrong choice.
• accidentally emphasizes lack of intention (it happened by accident).

Quick Examples

• “I mistakenly thought the deadline was Friday.” (wrong belief)
• “I accidentally deleted the file.” (unintended action)

When “By Mistake” Is Even Clearer

In instructions, apologies, and quick corrections, by mistake can sound cleaner than any -ly adverb.

• “I sent the wrong invoice by mistake.”
• “Your order was marked delivered by mistake.”

Common Mistakes And Quick Fixes

• Wrong: “I mistakingly sent the invoice to the wrong client.”
  Right: “I mistakenly sent the invoice to the wrong client.”
• Wrong: “She mistakingly believed the store opened at 10.”
  Right: “She mistakenly believed the store opened at 10.”
• Wrong: “I did it mistakenly” (when you mean a pure accident with no judgment)
  Better: “I did it accidentally” or “I did it by accident.”

Everyday Examples In US English

• Work Email: “I mistakenly attached the older file—sending the updated version now.”
• Customer Support: “Your order was mistakenly marked as delivered. We’re fixing it.”
• Text Message: “I mistakenly went to the wrong coffee shop. Be there soon.”
• School Writing: “The article mistakenly claims the event happened in May.”
• Everyday Talk: “I mistakenly thought the meeting started at 3.”

Comparison Table

Dictionary-Style Word Details

Part Of Speech

• mistakenly: adverb
• mistakingly: adverb

Meaning

• mistakenly: wrongly; by mistake; unintentionally/in error
• mistakingly: in a mistaking manner (rare/marked in modern usage)

Synonyms

• mistakenly: incorrectly, wrongly, erroneously, in error, by mistake
• mistakingly: usually replaced by mistakenly or by mistake in modern editing

Phrases Commonly Used With “Mistakenly”

• mistakenly believed
• mistakenly assumed
• mistakenly identified
• mistakenly sent
• mistakenly reported

FAQs

Is mistakingly or mistakenly correct?

Mistakenly is the standard choice in U.S. English. Mistakingly exists in reference works, but it is uncommon and often avoided in modern writing.

Is mistakingly a real word?

Yes. It appears in major references, including Merriam-Webster and the Oxford English Dictionary.

Does mistakenly mean “by accident”?

Often, yes—but it can also mean “wrongly believed.” If you want to highlight pure lack of intent, accidentally may fit better.

Can I use mistakingly in formal writing?

It is usually best to avoid it. Many editors will prefer mistakenly because it reads more natural and familiar.

What is the easiest safe replacement?

Use mistakenly. If you want extra clarity, rewrite as by mistake.

Will readers notice mistakingly?

Many will. Because it is uncommon, some readers may pause or assume it is an error even when you meant it intentionally.

Mini Quiz

Choose the best option.

• I ___ thought the store opened at 10.
• She ___ sent the email to the wrong person.
• The chart was ___ labeled in the draft.
• I hit “reply all” ___, not on purpose.
• He ___ believed the rumor was true.

Answer Key

• mistakenly
• mistakenly
• mistakenly
• accidentally
• mistakenly

Conclusion

For clear, natural U.S. writing, mistakenly is the better choice. It is the standard form in major dictionaries and the one readers expect.

Mistakingly exists, but it is rare enough to feel risky in everyday writing. When in doubt, keep it simple: use mistakenly—or rewrite as by mistake.