That shit ain't the truth vs That's a lie

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

That shit ain't the truth

Informal Top 2,000 (common)

That's a lie

Common idiom

Most formal: That's a lie Most common: That shit ain't the truth

	That shit ain't the truth	That's a lie
Pronunciation	🇬🇧 //ðæt ʃɪt eɪnt ðə truːθ// 🇺🇸 //ðæt ʃɪt eɪnt ðə truθ//	🇬🇧 //ðæts ə laɪ// 🇺🇸 //ðæts ə laɪ//
Meaning	That statement is not true.	It's not true.
Example	When he said he won the lottery, I thought, 'That shit ain't the truth'.	When he claimed he finished the project on time, I thought, 'That's a lie.'
Register	Informal	Neutral
How common	Top 2,000 (common)	Common idiom
Collocations	ain't the truth, speak the truth, tell the truth	tell a lie, caught in a lie, big lie
Common mistakes	Confused with formal expressions like 'That is not true.', Using it in formal writing contexts., Overusing the expression can make conversations sound unprofessional.	Use 'lies' instead of 'lie' when referring to multiple falsehoods., Confuse with 'lying' which refers to the act of being in a horizontal position.
Usage notes	This phrase is very informal and often used in casual conversations. Avoid using it in formal situations or writing. It conveys strong emotion or disbelief.	Used to express disbelief or accusation. Avoid in formal contexts.

See it in real clips

But that shit ain't the truth.

That shit ain't the truth

House Of Cards › S1 E1

because we both know that's a lie.

That's a lie

Frequently asked questions: That shit ain't the truth vs That's a lie

What's the difference between That shit ain't the truth and That's a lie?

That shit ain't the truth: That statement is not true. That's a lie: It's not true.

Which is more formal: That shit ain't the truth and That's a lie?

That's a lie is the most formal of these.

Which is more common: That shit ain't the truth and That's a lie?

That shit ain't the truth is the most common in everyday English.

Can you show an example of each?

That shit ain't the truth: When he said he won the lottery, I thought, 'That shit ain't the truth'. That's a lie: When he claimed he finished the project on time, I thought, 'That's a lie.'

Can I use That shit ain't the truth and That's a lie interchangeably?

Not always. That shit ain't the truth and That's a lie 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.