Yes, you will (do) personally owe the balance, the only question is to who. If the other driver carries under-insured coverage, his insurer may pay the balance of the damages to that driver - and turn around and sue you for that amount.  Or, if they do not recover from their own insurer, then the other driver may sue you directly.  Either way, you are likely to be on the hook, the only question is who takes the risk that they can't recover everything owed from you - the other driver or his insurance company. If you caused the damage, you owe one of the two, period. If you did not carry enough insurance to cover all the damages, your personal assets are at risk for the balance. That is, after all, the whole concept of insurance.