See exactly how each loan payment splits between principal and interest over the life of the loan.
Amortization is the process of spreading a loan into a series of fixed payments. Each payment covers interest on the remaining balance plus a portion of the principal. Early payments are mostly interest; later payments are mostly principal.
Adding even $100/month extra toward principal on a $250,000 mortgage at 6.5% saves over $60,000 in interest and pays off the loan nearly 5 years early.