that'll be the day!

INFORMAL
This page is about the conversational phrase that'll be the day!

Meaning

You can say this if you don't think something will ever happen or become true.

For example

  • "I'm going to quit drinking and smoking and exercise more."
    "That'll be the day!"

  • Adam said, "In the free-market economy, workers will also get rich," and Karl scoffed and said, "Hah! That'll be the day!"

Quick Quiz

You can say "That'll be the day!" if you think something

a. is sure to happen

b. is likely to happen

c. is unlikely to happen

Contributor: Matt Errey