So you have established an allowance. You pay it out on Saturday mornings. But it is Friday night and your teen has run out of money. Some friends have invited them to go to a movie and the following conversation ensues...
Teen: "Mom, I ran out of money. Can I just borrow some and you can take it out of my allowance tomorrow?"
Mom: " I am so sorry. I give allowance on Saturday. Maybe you could use the money you have set aside for clothes and then pay yourself back?"
Teen: "I already used that."
Mom: "Rats. Well don't worry, I pay out allowances on Saturday."
Teen: "But what about tonight. I need to go to the movies and I don't have any money."
Mom: I am so sorry, but I will definitely give out your allowance on Saturday.
You get the drift. The teen may not be happy but they will learn a lesson about budgeting to make the $$$ supply last longer. In the process they'll also learn the important skill of delayed gratification. The Mom did not lecture, warn, or rescue. (Notice how important it is to establish the rule of paying an allowance at the same time every week.)