Unless the parties agree in writing to a longer period of time, if the claimant fails to file a cause of action in circuit court prior to a date one hundred twenty days after the demand or offer was received, then the court shall not award prejudgment interest to the claimant. If the claimant is a minor or incompetent or deceased, the affidavit may be signed by any person who reasonably appears to be qualified to act as next friend or conservator or personal representative. If the claim is one for wrongful death, the affidavit may be signed by any person qualified pursuant to section 537.080 to make claim for the death. Nothing contained herein shall limit the right of a claimant, in actions other than tort actions, to recover prejudgment interest as otherwise provided by law or contract.
§ 408.040, RSMo