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Hi

Would you say that the following sentences are OK for an informal coversation?

Why did you renege on your promise?

Why did you renege on your word?

Thanks,

Tom
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Hi,

We commonly say

Why did you break your promise?

Why did you break your word?

Clive
Comments  
"renege" is not a very conversational word. You might get some blank looks.

I'd probably say "Why did you go back on your promise/word?"
 Clive's reply was promoted to an answer.