Loan & mortgage payment

A loan payment looks like a single number, but it is really the answer to a question with four inputs: how much you borrowed, the rate, the term, and how often interest compounds. Change any one of them and the number moves. Understanding which lever does what is the difference between accepting the first quote and negotiating the one that actually costs you less.

Where the number comes from

Every fixed-rate amortising loan. Mortgage, car loan, personal loan, student refinance. Uses the same formula. The payment is set so that the balance reaches exactly zero on the final scheduled month, with interest charged each month on whatever is still outstanding.

The consequence worth internalising is that the payment does not scale evenly with the rate. Going from 6% to 7% on a $360,000 thirty-year mortgage adds roughly $240 a month. Going from 12% to 13% on the same balance adds about $280. The higher the rate, the more each additional point costs you, which is exactly why rate shopping matters most for borrowers with weaker credit files, the group least likely to do it.

Why early payments barely touch the balance

Interest is charged on the outstanding balance, and at the start of a loan the outstanding balance is nearly the whole amount. On a $360,000 loan at 6.75%, the first month's interest is $2,025. If the payment is $2,335, only $310 of it reduces what you owe. That ratio is not a trick or a fee structure, it is arithmetic, and it reverses slowly as the balance falls.

The crossover month, where more of the payment goes to principal than interest, is the single most useful number the calculator gives you. On a thirty-year loan at typical rates it arrives somewhere around year eighteen. On a fifteen-year loan at the same rate it arrives in year four. This is the real reason a shorter term costs so much less in total: you spend far less of the loan's life paying rent on money you have already agreed to repay.

The term trade-off, in numbers

The thirty-year payment is $851 a month lighter than the fifteen-year, and costs $267,100 more. Neither is the right answer in isolation. A longer term with the difference invested or directed at higher-rate debt can beat a shorter one; a longer term with the difference absorbed into lifestyle spending does not. What the table settles is that the choice is expensive either way, so it deserves more than a shrug.

What this payment does not include

For a mortgage, the figure above is principal and interest. Your actual monthly obligation usually also carries property tax, homeowner's insurance, and. If your down payment was under 20% on a conventional loan, mortgage insurance. Together these commonly add 25% to 40% on top of the principal-and-interest number, and on a low-priced home in a high-tax county they can add more than half.

• Property tax varies from well under 0.5% of assessed value a year to over 2% depending on the state and county.
• Homeowner's insurance is priced on the rebuild cost, not the purchase price, and has risen sharply in wildfire and coastal-storm regions.
• Private mortgage insurance typically runs 0.3% to 1.5% of the loan a year and can usually be removed once you reach 20% equity, but you generally have to ask.
• HOA dues, where they apply, are not part of the loan and are not escrowed, but they are just as unavoidable each month.

What extra payments actually buy

Any amount paid above the scheduled payment goes straight to principal, which means the interest on that principal is never charged. The saving is therefore larger than the payment itself, and larger still the earlier it happens. An extra $200 a month from month one on the thirty-year loan above clears it roughly five and a half years early and saves around $124,000 in interest.

Two practical notes. First, tell the servicer the extra amount is for principal. Otherwise it may be held as a prepaid instalment or applied to escrow, which does not reduce interest. Second, prepaying a 6.75% mortgage is a guaranteed 6.75% return, which is excellent against a savings account and poor against a 24% credit card balance. Order matters more than enthusiasm.