What is actually in a mortgage payment
Lenders quote principal and interest, because that is the part of the payment that goes to them. The cheque you write every month is bigger. The industry shorthand is PITI:
- Principal — the slice that reduces what you owe. Small at first, and that is not an accident.
- Interest — the cost of borrowing, charged on the balance you still owe. Large at first, shrinking every month.
- Taxes — property tax, usually collected monthly into an escrow account and paid on your behalf.
- Insurance — homeowners insurance, also normally escrowed.
Then two extras that are not in the acronym but are very much in the payment: PMI if you put down less than 20%, and HOA or service charges if the property has them.
The gap between the quoted number and the real one is often 25–35% of the payment. That is the difference between comfortable and stretched.
The payment formula
L is the loan amount, i the monthly rate (annual rate divided by 12) and n the number of months. Everything else in your payment — tax, insurance, PMI, HOA — is a simple monthly share of an annual cost, added on top.
Why the early years feel like nothing is happening
Interest is charged on what you still owe, so at the start almost all of it is interest. On a 30-year loan at 6.5%, roughly the first third of your payment goes to principal in year one — and it takes about eighteen years before the split tips past halfway.
This is also why an extra payment made early is worth so much more than the same payment made late. Every unit of principal you retire in year two stops accruing interest for twenty-eight more years.
PMI is temporary, and it is on you to end it. Private mortgage insurance protects the lender, not you, and typically costs 0.3–1.5% of the loan a year. It normally has to be cancelled once your balance falls to 80% of the home's value — but in many cases you have to ask. This calculator drops PMI automatically at that point, so the payment you see later is lower than the one you start with.
What an extra payment really buys
Adding even a modest amount to the principal each month has an effect out of proportion to its size, because it compounds against you in reverse. Enter a figure in the extra payment field and the calculator shows two things: how many years come off the loan, and how much interest never gets charged.
Before you do it, though, check the order of operations. Extra mortgage payments are effectively a guaranteed return equal to your mortgage rate. If you are carrying credit card debt at 20%, that comes first — it is not close. And a mortgage payment cannot be un-made: money in the house is money you cannot reach without selling or borrowing again, which is why the emergency fund comes first too.
How much house can you afford?
Lenders answer this with your debt-to-income ratio: your total monthly debt payments, including this one, against your gross income. Common guidance keeps housing under 28% and all debt under 36%, and most mortgage programmes stop somewhere around 43%.
Being approved for a number is not the same as it being wise. The bank is underwriting the loan, not your life.