Personal Loan Interest & APR Explained: Base Rates vs True Borrowing Cost
Understand interest rate calculations on personal loans, monthly compounding, APR formulas, and how upfront origination fees shift true borrowing costs.
By Sarah Jenkins, CFA
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Reviewed by David Vance, CFP
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5 min read
Base Interest Rate vs Annual Percentage Rate (APR)
Your base interest rate determines the exact percentage of your remaining principal balance paid to the lender in monthly interest. However, your Annual Percentage Rate (APR) represents the true comprehensive cost of borrowing because it combines base interest rate + mandatory upfront origination fees.
Effective APR Formula
Effective APR = Base Interest Rate + (Upfront Fees ÷ Loan Term Years)