Principal
Principal is the original amount you borrow or invest, separate from the interest on it. On a loan, each payment splits between interest (the cost of borrowing) and principal (which actually shrinks the debt) — and early on, most of a mortgage payment goes to interest.
Extra money aimed at principal shortens the loan and cuts total interest, because every future interest charge is calculated on a smaller balance — and the earlier it lands, the more it saves, since early payments are mostly interest. One practical trap undoes this regularly: unless the payment is explicitly designated principal-only, many servicers apply it to the next month's instalment instead. That marks you paid ahead rather than reducing the balance, so the interest saving never happens. Check how yours handles it, and check the statement afterwards. An amortisation schedule shows the split shifting toward principal over the life of the loan, and is the clearest way to see what an extra payment actually bought.
Put it to work
Mortgage Calculator
Estimate your monthly mortgage payment with taxes, insurance, PMI and HOA — plus total interest and a full amortization breakdown. Free, fast, no signup.
Amortization Calculator
Build a complete amortization schedule for any loan: payment, year-by-year principal vs interest split, and the effect of extra payments.
Loan Calculator
Calculate the monthly payment, total interest, and payoff date for any personal, auto, or fixed-rate loan — and see how extra payments shorten it.