All of a sudden vs Next thing you know

When to use each in English, with meaning, register, and examples.

All of a sudden

Top 2,000 (common)

Next thing you know

Informal Top 3,000 (common)

Most formal: All of a sudden Most common: All of a sudden

	All of a sudden	Next thing you know
Pronunciation	🇬🇧 //ɔːl əv ə ˈsʌdən// 🇺🇸 //ɔl əv ə ˈsʌdən//	🇬🇧 //nɛkst θɪŋ jə nəʊ// 🇺🇸 //nɛkst θɪŋ jə noʊ//
Meaning	Unexpectedly or very quickly.	Then something happens quickly or unexpectedly.
Example	All of a sudden, it started to rain heavily.	I was watching TV, and the next thing you know, it's midnight!
Register	Neutral	Informal
How common	Top 2,000 (common)	Top 3,000 (common)
Collocations	all of a sudden, a loud noise, all of a sudden, they appeared, all of a sudden, it happened	and the next thing you know, next thing you know, it's, before you know it, the next thing you know
Antonyms	gradually, slowly, over time	previously, earlier, beforehand, last thing you realize
Common mistakes	Using in overly formal contexts., Confusing with similar phrases like 'suddenly.', Omitting 'of' in the phrase.	Using it in a formal context., Confusing it with 'next thing,' which is less specific., Overusing it in conversations.
Usage notes	Used to describe a change that happens suddenly. Suitable for both spoken and written English; avoid in formal writing.	Used in casual conversation to describe a sudden change or event. Not suitable for formal writing.

See it in real clips

Agatha Christies Poirot › S1 E1

Why should Japp want Simpson all of a sudden?

Friends › S1 E1

All of a sudden, the phone starts to ring.

Breaking Bad › S1 E2

But then all of a sudden we're off the main road

Agatha Christies Poirot › S1 E1

Why should Japp want Simpson all of a sudden?

Friends › S1 E1

All of a sudden, the phone starts to ring.

All of a sudden

Ted Lasso › S1 E1

Next thing you know,

Next thing you know

Frequently asked questions: All of a sudden vs Next thing you know

What's the difference between All of a sudden and Next thing you know?

All of a sudden: Unexpectedly or very quickly. Next thing you know: Then something happens quickly or unexpectedly.

Which is more formal: All of a sudden and Next thing you know?

All of a sudden is the most formal of these.

Which is more common: All of a sudden and Next thing you know?

All of a sudden is the most common in everyday English.

Can you show an example of each?

All of a sudden: All of a sudden, it started to rain heavily. Next thing you know: I was watching TV, and the next thing you know, it's midnight!

Can I use All of a sudden and Next thing you know interchangeably?

Not always. All of a sudden and Next thing you know are related and overlap in some contexts, but they differ in register, how common they are, and usage, so swapping one for another can change the meaning or tone. Check the differences above before substituting.