Idiom: Cost an Arm and a Leg
very expensive
Examples
- That watch cost an arm and a leg.
Key rules
- Cost an arm and a leg means be very expensive
- It is informal and used with "it costs" or "it cost me"
- The verb changes for the subject: it costs an arm and a leg
- The phrase can describe goods and services
Common mistakes
- It costs an arms and a legs → It costs an arm and a leg
💡 Tip: Use it for everyday prices in speech; use "expensive" in formal writing.