It is not necessary that the claim sought to be found in favor of the creditor and against the estate of the deceased shall be due and payable. It is sufficient if the claim is just and true, and then it shall be allowed when presented in the same manner as a claim that is due. There shall be a rebate of interest, however, to be earned from the time the allowance to the time such debt would have become due according to the terms of the contract.5