You could, but because it wasn't part of your original contract, the courts will likely find it invalid. You're not allowed to impose interest that was not agre

You could, but because it wasn't part of your original contract, the courts will likely find it invalid. You're not allowed to impose interest that was not agreed upon beforehand. Also, part of a trial is to make the judge/jury like you. No matter how right you are, if you're an arrogant person, you won't get much sympathy. It's much better to wait for the courts to settle the issue, where a judge could impose punitive damages (interest).