Principal the money you start with or put in. Where it's taught Compound Interest & the Time Value of MoneyLoans & Amortization Try it with a calculator Compound Interest CalculatorLoan Amortization Calculator Appears in 16 other lessons Credit Cards & the Minimum-Payment TrapEmergency Fund or Pay Off Debt First?Payday Loans: What a 'Small' Two-Week Fee Actually CostsBorrowing From Your Own 401(k): The Loan That Sounds FreeCo-Signing a Loan: Vouching for Someone Else's DebtBonds: Why Their Prices Move BackwardsCashing Out a 401(k) When You Leave a Job — vs. Rolling It OverHow Much House Can You Actually Afford? The 28/36 RuleRent vs Buy: It's a Break-Even, Not a BattleMortgage Points: Buying Down Your Rate Is a Break-EvenRefinancing a Loan: When Does It Actually Pay Off?HELOC: Borrowing Against Your HomePay Down Debt or Invest? The Guaranteed-Return CrossoverReal-Estate Investing: Cap Rate, Cash Flow, and the Magic (and Menace) of LeverageAnnuities: Buying Yourself a Paycheck for LifeLifestyle Creep: Bank Your Raises or Spend Them? Related terms AmortizationCompounding periodExtra principal paymentInterestRate of returnTermTime value of money