Plain-language lessons on how mortgages actually work.

When you make a mortgage payment, most of it isn't going where you think. Lenders bundle four things into one monthly bill: Principal, Interest, Taxes, and Insurance — collectively called PITI.

The taxes and insurance portions go into an escrow account. The lender holds that money on your behalf and pays your county property tax bill and your homeowner's insurance premium when they come due. You don't get to skip them, and you don't get to invest the cash in the meantime.

Why does the bank do this? Because if you fail to pay property taxes, the county can put a lien on the house ahead of the mortgage. And if the house burns down without insurance, the bank loses its collateral. Escrow protects the lender first, you second.

Practical takeaway: when your property tax assessment or insurance premium goes up, your monthly payment goes up — even on a 'fixed-rate' loan. Re-check your escrow analysis every year.

If your down payment is less than 20% of the purchase price, you'll almost always be required to pay Private Mortgage Insurance, or PMI. It typically costs between 0.3% and 1.5% of the loan amount per year, billed monthly.

Read that again: you pay it, but it insures the lender against your default. You get nothing if you stop paying — no payout, no equity, no benefit.

The good news: PMI is not permanent. Under federal law, lenders must automatically cancel PMI when your loan balance reaches 78% of the original home value (assuming you're current on payments). You can also request cancellation at 80% loan-to-value (LTV), which is usually faster if your home has appreciated.

Strategy: if you're close to 20% down, scraping together a little extra to cross that line can save you thousands. If you're far below, accept PMI as the price of getting in early, and plan to refinance or request removal as soon as you hit the threshold.

A mortgage payment is a fixed amount, but the split between interest and principal changes every single month. Early on, you're paying interest on the entire loan balance, so almost the whole check goes to the bank. As the balance shrinks, more of each payment chips away at principal.

On a 30-year loan at 7%, you typically don't cross the 50/50 line — where principal equals interest — until somewhere around year 18. That's the amortization curve doing exactly what it was designed to do: front-load the lender's profit.

One extra principal payment per year can cut a 30-year loan by 4–5 years and save tens of thousands in interest. Why? Every dollar of extra principal eliminates the interest that dollar would have generated for the remaining life of the loan.

Practical move: even rounding your payment up to the nearest $100, marked 'apply to principal,' compounds dramatically over decades. Always confirm with your servicer that extra payments go to principal, not future installments.

A 30-year fixed mortgage locks your interest rate for the entire life of the loan. An Adjustable-Rate Mortgage (ARM) gives you a lower rate for an initial period — commonly 5, 7, or 10 years — and then resets annually based on a market index plus a margin.

A 5/1 ARM, for example, is fixed for five years and then adjusts every year after. The catch: those adjustments can move dramatically. After the 2022–2023 rate surge, many ARM holders saw monthly payments jump by 40–60% at reset.

ARMs make sense in narrow cases: you're confident you'll sell or refinance before the reset, you can comfortably afford the worst-case payment at the rate cap, or rates are abnormally high and you expect them to fall.

ARMs are dangerous when: you're stretching to qualify at the teaser rate, you have no plan B if rates rise, or you assume you can always refinance. (You can't — credit, income, or home value changes can lock you out.) For most buyers, the fixed rate is the cheaper form of insurance.

Debt-to-Income (DTI) is the single most important number in mortgage underwriting. It measures the percent of your gross monthly income that goes to debt payments. Lenders calculate two versions.

Front-end DTI (the 28% rule): housing payment divided by gross income. Traditional guidance says keep this under 28%. Housing here means PITI plus HOA and PMI — the full monthly cost of ownership.

Back-end DTI (the 36% rule): housing payment plus all other monthly debt (car loans, student loans, credit card minimums, personal loans) divided by gross income. Traditional ceiling: 36%. The federal Qualified Mortgage rule allows up to 43%, and some loan programs stretch to 50%.

Here's the trap: lenders will frequently approve you at the legal maximum, not the comfortable maximum. A 43% DTI mortgage technically qualifies, but it leaves almost nothing for savings, repairs, or emergencies. The 28/36 rule isn't a regulation — it's a safety margin built by decades of foreclosure data. Stay close to it.