Client has overpaid: Legal obligation to return w/ interest?

If a client has over paid and it only gets noticed by either party after awhile what is the standard practise for resolving it? I know that of course the overpayment will have to be returned, but could there be a liabilty to also return the overpayment with interest, even though the mistake came from the client themselves?

Re: Overpaid: Legal obligation to return w/ interest?

No, I have never heard of a mistake having to be repaid with interest.

Thanks.