How Mortgage Payments Are Calculated: Principal, Interest & Amortization Schedules

A step-by-step breakdown of the standard fixed-rate mortgage payment formula and long-term interest equity building.

By AnyCalcHub Financial Analysis Desk

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1. The Standard Fixed-Rate Mortgage Formula

Fixed-rate mortgage payments are calculated using standard annuity amortization math, ensuring equal monthly installments throughout the loan term.

Mathematical Formula

M = P × [r(1 + r)^n] / [(1 + r)^n - 1]

Step-by-Step Worked Example

Loan Amount (P)$400,000

Annual Rate6.8%

Term30 Years (360 Months)

Step 1:Monthly rate: r = 0.068 / 12 = 0.005667

Step 2:Compounding factor: (1 + r)^360 = 7.575

Step 3:Monthly payment: 400,000 × (0.005667 × 7.575) / (7.575 - 1) = $2,607.72

Final Result: Monthly Principal & Interest Payment: $2,608

Common questions and mathematical nuances for this calculation.

The core formula computes Principal & Interest (P&I). Full escrow payments (PITI) also add monthly property taxes and homeowners insurance.

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