Principal vs. Interest: What Are You Actually Payaying?
Mike Starr
Founder, MortgageWizardTools · M.S. Organizational Management
Every mortgage payment is split between two things: principal (reducing your loan balance) and interest (the cost of borrowing). Understanding this split is essential for making smart decisions about extra payments, refinancing, and payoff strategy.
What Is Principal?
Principal is the amount you borrowed. If you take out a $350,000 loan, your starting principal is $350,000. Each month, a portion of your payment reduces this balance. As the principal shrinks, the interest you owe each month also shrinks — because interest is calculated on the remaining balance.
What Is Interest?
Interest is what the lender charges for lending you money. It is calculated each month on your remaining principal balance. On a $350,000 loan at 6.5%, your first month interest is about $1,896. By year 10, it might be around $1,500. By year 25, under $700.
The Amortization Split
| Year | Principal | Interest | Total Payment |
|---|---|---|---|
| Year 1 | ~$3,600 | ~$22,700 | ~$26,300 |
| Year 15 | ~$8,800 | ~$17,500 | ~$26,300 |
| Year 29 | ~$24,000 | ~$2,300 | ~$26,300 |
Early payments barely dent your balance. That is why extra payments made early in the loan save dramatically more interest than the same extra payment made later.
Why This Matters
If you are deciding between a 15-year and 30-year loan, between making extra payments or investing, or whether to refinance, understanding the principal-interest split helps you see the real financial impact. Use our Amortization Calculator to see your exact split.
Key Takeaways
- •Principal reduces your loan balance; interest is the cost of borrowing
- •Early payments are mostly interest, later payments are mostly principal
- •Extra payments made early save more interest than those made later
- •The interest portion shrinks automatically as your balance decreases