A mortgage is probably the biggest financial commitment of your life. Understanding how it works can save you tens of thousands of dollars.
Mortgage Basics
A mortgage consists of three elements:
- The principal: the amount the lender gives you
- The interest: the cost of borrowing, calculated on the remaining balance
- Insurance/PMI: required if your down payment is less than 20%
The Monthly Payment
Your payment includes principal and interest. Early on, most of your payment goes to interest. Later, most goes to principal.
| Year | Payment | Principal | Interest |
|---|---|---|---|
| 1 | $1,500 | $500 | $1,000 |
| 10 | $1,500 | $850 | $650 |
| 25 | $1,500 | $1,400 | $100 |
This is why making extra payments early in the loan is far more effective than later.
Fixed Rate vs Variable Rate
Fixed Rate
- The rate never changes for the entire loan term
- Predictable, constant monthly payment
- Best for most borrowers
Variable Rate (ARM)
- The rate adjusts based on a benchmark index
- Often starts lower than fixed rates
- Can increase significantly over time
Tip: In a rising rate environment, a fixed-rate mortgage protects you. ARMs can be useful if you plan to sell or refinance within 5-7 years.
APR: The True Cost of Borrowing
The APR (Annual Percentage Rate) includes all costs:
- Interest rate
- Origination fees
- Mortgage insurance (PMI)
- Closing costs
- Points
Always compare APRs between offers, not just interest rates.
Example
| Offer | Interest Rate | Fees | APR |
|---|---|---|---|
| Lender A | 6.50% | $5,000 | 6.85% |
| Lender B | 6.75% | $1,500 | 6.82% |
Lender B has a higher rate but lower APR → it's cheaper overall.
How Much Can You Borrow?
Lenders use the debt-to-income ratio (DTI) - typically capped at 43%:
DTI = (Total Monthly Debt Payments / Gross Monthly Income) × 100
Example
Gross monthly income: $7,000 Max DTI: 43% → max total debt payments: $3,010/month
Loan Term Changes Everything
For the same $300,000 loan at 6.5%:
| Term | Monthly Payment | Total Interest Paid |
|---|---|---|
| 15 years | $2,613 | $170,340 |
| 20 years | $2,238 | $237,120 |
| 30 years | $1,896 | $382,560 |
Going from 15 to 30 years cuts the payment by $717 but costs $212,220 more in interest.
The Down Payment
A larger down payment means:
- Lower monthly payment
- Better interest rate
- No PMI (if 20%+)
| Down Payment | Monthly PMI | Effect on Rate |
|---|---|---|
| 3-5% | $100-250/month | Higher rate |
| 10% | $50-150/month | Standard rate |
| 20%+ | $0 | Best rate |
The 20% Sweet Spot
Putting 20% down eliminates PMI entirely, which can save $150-300/month. On a 30-year loan, that's $54,000-$108,000 in total savings.
Refinancing
Refinancing replaces your current mortgage with a new one, typically at a lower rate.
When It Makes Sense
- Current rates are 1%+ lower than your existing rate
- You plan to stay in the home long enough to recoup closing costs
- You want to switch from ARM to fixed
The Break-Even Calculation
Break-even months = Closing costs / Monthly savings
If refinancing costs $4,000 and saves $200/month: break-even in 20 months. If you'll stay longer, refinance.
Making Extra Payments
Extra payments can dramatically reduce your loan term and interest costs.
Example
$300,000 loan at 6.5% for 30 years:
- Normal payments: pay $382,560 in interest over 30 years
- Extra $200/month: pay $271,400 in interest, done in 23 years
- Savings: $111,160 and 7 years
Biweekly Payments
Paying half your monthly payment every two weeks results in 13 full payments per year instead of 12. This alone can shave 4-5 years off a 30-year mortgage.
Conclusion
Before signing a mortgage, compare APRs (not just rates), shop at least 3 lenders, consider the total cost over the life of the loan, and choose a payment you can comfortably afford with room to spare.