Guide

Mortgages explained

A mortgage is a secured loan: the lender gives you money to buy a home, and the home itself is collateral. Miss enough payments and the bank can foreclose. For most households it is the largest debt they will ever carry — often 15 or 30 years of monthly payments tied to interest rates that move with the broader economy. Understanding how principal, interest, taxes, and insurance combine into your monthly bill — and what lenders look at before they approve you — prevents the most expensive mistake in personal finance: buying too much house at the wrong rate. This guide walks through loan types, payment math, down-payment rules, private mortgage insurance, the approval process, and a checklist before you sign.

How a mortgage works

You borrow a principal amount — say $400,000 on a $500,000 purchase with a 20% down payment. Each month you pay a blend of principal (paying down the loan balance) and interest (the lender’s fee for lending). Early in a 30-year loan, most of the payment is interest; later years shift toward principal. That schedule is called amortization.

The quoted annual percentage rate (APR) includes interest plus certain lender fees, giving a better apples-to-apples comparison than the note rate alone. Your monthly housing cost is usually summarized as PITI:

Principal — loan paydown
Interest — cost of borrowing
Taxes — property taxes (often escrowed by the lender)
Insurance — homeowners insurance (also often escrowed)

Lenders and budgeting tools often add HOA fees and PMI (below) on top of PITI. A common rule of thumb — spend no more than 28% of gross monthly income on housing and 36% on all debt — is a starting point, not a permission slip to max out.

Fixed-rate vs adjustable-rate (ARM)

A fixed-rate mortgage locks the interest rate for the entire term. Your principal-and-interest payment stays the same (escrowed taxes and insurance can still change). Fixed rates dominate U.S. home loans because they remove payment shock when the yield curve shifts or the Fed hikes.

An adjustable-rate mortgage (ARM) starts with a lower “teaser” rate for a fixed period — commonly 5, 7, or 10 years — then resets periodically based on a benchmark index plus a margin. ARMs can make sense if you plan to sell or refinance before the first reset, or if you can absorb higher payments if rates rise. The risk: a 2-point rate jump on a $400,000 balance adds roughly $500/month to principal and interest. Read the adjustment caps (how much the rate can move per period and over the life of the loan) before choosing an ARM to save a few tenths on the initial rate.

15-year vs 30-year terms

A 30-year fixed spreads payments over 360 months — lower monthly cost, more total interest paid. A 15-year fixed charges a lower rate and builds equity faster but demands a higher monthly payment. On a $400,000 loan at 6.5% (30-year) versus 5.8% (15-year illustrative spread), the 30-year payment is roughly $2,530 principal and interest; the 15-year is about $3,340 — but total interest over the life of the loan can differ by hundreds of thousands of dollars.

The right term depends on cash flow, other goals (retirement contributions, childcare), and opportunity cost. Paying extra principal on a 30-year loan without refinancing offers flexibility — you can stop prepaying if income drops — whereas a 15-year contract is less forgiving.

Down payment, LTV, and PMI

The down payment is cash you bring at closing; the mortgage covers the rest. Loan-to-value (LTV) is loan amount divided by appraised value. An $80,000 down payment on a $400,000 home is 20% down, 80% LTV.

Put less than 20% down on a conventional loan and lenders typically require private mortgage insurance (PMI) — an extra monthly premium protecting the lender if you default. PMI does not build equity for you; it is pure cost until LTV drops to 78% through paydown or appreciation (rules vary — request removal in writing once you hit 80%). FHA loans allow 3.5% down with mortgage insurance for the life of the loan in many cases; VA loans for eligible veterans often require zero down with no PMI but include a funding fee.

A larger down payment reduces monthly payment, total interest, and PMI risk — but depleting your emergency fund to hit 20% can leave you one roof leak away from credit-card debt. Keep a post-closing reserve of several months of PITI plus maintenance.

What lenders evaluate

Credit score

Mortgage pricing is tiered by credit score. A borrower at 760 might get a rate 0.5% lower than someone at 680 on the same loan — tens of thousands of dollars over 30 years. Pay down card balances, avoid new credit inquiries, and fix report errors 6–12 months before applying.

Debt-to-income ratio (DTI)

Front-end DTI is housing costs divided by gross monthly income; back-end DTI adds all recurring debts (auto loans, student loans, minimum card payments). Many conventional lenders cap back-end DTI around 43–50% with strong compensating factors. A $1,500 student loan payment can disqualify you from a home you thought you could afford on income alone.

Income, assets, and employment

Lenders verify W-2s, tax returns, bank statements, and employment history (typically two years). Self-employed borrowers face extra scrutiny — net income after deductions matters, not gross revenue. Gift funds for down payments require a paper trail and donor letter stating no repayment expected.

Pre-qualification vs pre-approval

Pre-qualification is a rough estimate based on stated income — useful for browsing. Pre-approval involves a hard credit pull and document review; sellers treat it seriously in competitive markets. Pre-approval letters expire; rate locks are separate and usually last 30–60 days through closing.

Closing costs and points

Beyond the down payment, buyers pay closing costs — typically 2–5% of the loan amount. Line items include appraisal, title insurance, attorney or escrow fees, recording fees, prepaid property taxes, and initial escrow funding. Sellers sometimes contribute toward buyer closing costs in slower markets; in hot markets buyers absorb more.

Discount points are optional upfront fees that buy down the interest rate (one point = 1% of the loan amount). Points pay off only if you keep the loan long enough for monthly savings to exceed the upfront cost — calculate the breakeven in months. Conversely, lender credits raise your rate in exchange for lower closing costs — sensible if you plan to refinance or sell within a few years.

Rate shopping and loan types

Apply with multiple lenders within a 14–45 day window; credit bureaus generally count mortgage inquiries as one pull for scoring. Compare APR, not just the rate — a lower rate with higher fees can cost more over five years.

Conventional — not government-backed; best rates for strong credit and 20% down.
FHA — lower credit and down-payment floors; mortgage insurance often for life of loan.
VA — eligible military/veterans; no PMI, funding fee applies.
USDA — rural-eligible properties; zero down for qualified buyers.
Jumbo — loans above conforming limits (varies by county); stricter underwriting.

Refinancing replaces your existing loan — to lower rate, shorten term, or pull cash out (cash-out refi). The break-even rule: divide closing costs by monthly payment savings; if you sell before break-even, refinancing wasted fees. When rates fall sharply, refi booms; when they spike, purchase demand cools — the same rate cycle that shapes bond prices shapes housing affordability.

Buying vs renting — and REITs as exposure

Ownership builds equity and can hedge rent inflation, but it concentrates risk in one property and one local job market. Renting preserves mobility and avoids maintenance surprises; the trade-off is no forced savings via principal paydown. Run the numbers: total cost of ownership (PITI + maintenance ~1% of home value/year + opportunity cost of down payment) versus rent plus invested difference.

If you want real estate exposure without a mortgage, REITs offer liquid, diversified property income in a brokerage account — different risk profile than a single-family home you live in.

Common mistakes

Maxing the lender’s approval amount — approval is a ceiling, not a budget. Leave room for savings, kids, and maintenance.
Skipping the inspection — waiving inspection to win a bidding war can mean six-figure hidden repairs.
Ignoring ARM reset risk — teaser rates expire; model worst-case payment before signing.
Forgetting property tax reassessment — your payment can jump after purchase when the county resets assessed value to sale price.
Opening new credit before closing — a new car loan between pre-approval and closing can void approval.
Draining every dollar for down payment — closing costs plus first repair bill should not land on a 24% APR card.

Homebuyer checklist

Build or preserve a 3–6 month emergency fund separate from down-payment cash.
Pull credit reports; dispute errors; pay down revolving balances below 30% utilization.
Calculate target PITI using current rates — stress-test +2% on the rate.
Get pre-approved (not just pre-qualified) before serious shopping.
Compare Loan Estimates from at least three lenders within the same week.
Budget 2–5% of purchase price for closing costs on top of down payment.
Understand PMI rules and plan removal at 80% LTV if applicable.
Order a full home inspection; budget 1% of value annually for maintenance.
Do not change jobs, open new credit, or make large undocumented deposits before closing.
Review Closing Disclosure line-by-line against your Loan Estimate at least three days before signing.

Key takeaways

A mortgage is long-term secured debt — PITI, not just principal and interest, defines affordability.
Fixed-rate loans trade flexibility for certainty; ARMs trade lower initial payments for reset risk.
Down payment size drives PMI, monthly payment, and how much cash you keep for emergencies.
Credit score, DTI, and verified income determine approval and rate — optimize 6–12 months ahead.
Shop lenders, compare APR, and model closing costs and points breakeven before committing.
Buying is not always optimal — compare total ownership cost to rent and consider REITs for passive exposure.