Spending to Day vs. Spending in the Future?

For consumers, you should spend that next dollar to day if the marginal benefit is more than the marginal benefit of spending that dollar plus the interest it'll earn in the future. Don't forget that you earn interest on the money you save. Ultimately, what you'll hopefully be doing is applying what we economist call the rational rule. For example, i often tell my students to borrow money for that back packing trip that they keep dreaming about in university,. because in the uture, when they're busy with their careers, they'll be money rich, but time poor.