Understanding Mortgage Rates: Fixed, Variable, and the Math Behind Your Payment
A mortgage is usually the biggest loan you'll ever take out, and small differences in the interest rate translate into very large differences over 30 years. Knowing how rates work — and how to read an offer — is one of the highest-leverage financial skills you can develop.
How Mortgage Rates Are Set
Mortgage rates broadly track long-term government bond yields (most commonly the 10-year Treasury in the US), plus a spread that covers the lender's costs, risk, and profit margin. When the Federal Reserve raises short-term rates, long bond yields usually follow — and mortgage rates with them.
Your personal rate also depends on your credit score, down payment size, loan size, property type, and how the loan is sold to investors afterward.
Fixed vs Adjustable
Fixed-rate mortgages lock your rate for the full term (typically 15 or 30 years). Your monthly payment never changes. You pay a small premium for that certainty.
Adjustable-rate mortgages (ARMs) start at a lower rate for an initial period (commonly 5, 7, or 10 years) and then adjust periodically based on a benchmark index. Good if you expect to move before the adjustment, risky if rates rise and you don't.
Comparing Offers
Always compare APR (annual percentage rate), not just the headline interest rate. APR rolls in lender fees and points so two loans are actually comparable.
Run each offer through a mortgage calculator with your actual loan amount and term to see total interest paid. A 0.25% rate difference on a $400,000 30-year mortgage is roughly $20,000 over the life of the loan.
Points and Refinancing
'Points' are upfront fees you pay to lower your rate — typically 1% of the loan amount for a ~0.25% rate reduction. They pay off if you stay in the loan long enough.
Refinancing replaces your loan with a new one, usually at a lower rate. The rule of thumb: it makes sense if your new rate is at least ~0.75% lower and you'll stay in the home long enough to recoup the closing costs.
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Frequently Asked Questions
What credit score do I need for the best rate?
In the US, scores above 760 typically qualify for the best rates. Below that, rates step up in tiers.
How much down payment do I need?
Conventional loans typically expect 20% to avoid private mortgage insurance. FHA, VA, and other programs allow less.