How Interest Rates Change Your Payment

Interest is charged on the balance you still owe. Early in a thirty year loan that balance is nearly the whole loan, so a small change in the rate applies to a very large number for a very long time. That is why the difference between 6% and 6.5% does not feel like “half a percent.”

Everything below holds the loan constant at $320,000 over 30 years — a $400,000 house with 20% down — and changes only the rate.

From 5.5% to 7% is $312.04 more each month on the same house. Over a year that is $3,744.52 — real money that has to come from somewhere else in the budget.

Monthly figures understate it. Held to maturity, the rate decides how much of your money goes to the lender rather than to your own equity.

At 7%, total interest exceeds the amount borrowed. That is not unusual for a thirty-year loan; it is what a long term at a moderate rate costs.

Buyers usually do not hold the loan constant — they hold the payment constant. If $2,022.62 a month in principal and interest is what your budget allows, the rate decides how large a loan that supports.

A rise from 5.5% to 7% removes about $52,000 of borrowing power from the same monthly budget. This is why buyers who shopped a year apart can afford visibly different houses on identical incomes.

A lower rate can be bought with money paid at closing, which means two offers at different rates are not automatically ranked by rate.

• Discount points are an upfront payment that lowers the rate. Whether they pay off depends on how long you keep the loan.
• APR folds certain lender costs into a single rate figure. A large gap between the note rate and the APR signals that the rate is being bought with fees.
• Lender credits work in reverse: a higher rate in exchange for money toward closing costs. Useful when cash is the binding constraint.
• Rate locks matter. A quoted rate that is not locked can move before closing.

The Loan Estimate is built to make this comparison possible — how to read a Loan Estimate walks through which boxes to compare.

The practical takeaways are unglamorous and effective: collect Loan Estimates from more than one lender on the same day, compare APR alongside the rate, and ask what the rate would be with and without points.

Then test the range rather than a single number. Put your loan amount into the home payment calculator and move the rate up and down half a point in each direction. If the payment only works at the bottom of that range, the budget is tighter than it looks.

Note that no rate on this site is a quote. The rate field is an editable example so you can see how sensitive the payment is to it; your actual rate depends on your credit profile, loan program, down payment, term, points, and the market on the day you lock.