Tools
Know the whole payment before you shop
Principal, interest, taxes, and insurance are one number in real life. Here is how to build it, and how much house it means you can afford.
The four parts of a mortgage payment
People quote the first two and get surprised by the last two. Taxes and insurance commonly add 25% on top of principal and interest.
Principal
The part that pays down what you borrowed. Early in a 30-year loan it is a small slice; by year fifteen it is the larger one.
Interest
The cost of the money, set by your rate. At 6.375% APR on $400,000, the first month's interest alone is about $2,083.
Property taxes
Collected monthly into escrow and paid on your behalf. Rates vary enormously by county, from roughly 0.5% to over 2.2% of value a year.
Insurance
Homeowners insurance always, plus mortgage insurance if you put less than 20% down, plus flood coverage where it is required.
A worked example
A $475,000 home, 10% down, 30-year fixed at 6.375% APR, in a county taxing at 1.1%.
Notice that the last three lines add $735 a month, or 28% on top of principal and interest. Notice too that the mortgage insurance line disappears once you reach 20% equity, which on this loan takes about nine years of scheduled payments.
Rates current as of July 2026 and subject to change. Membership eligibility required. This is a demonstration website; rates, products, and figures shown are illustrative only.
Affordability
How much house you can actually afford
Underwriting uses two ratios. The front-end ratio is your housing payment against gross monthly income; the back-end ratio adds every other debt payment. Summit generally looks for 28% and 43%.
Using the number well
The calculator tells you what a lender will approve. These three habits tell you what you should actually spend.
Estimate with real local taxes
Look up the county rate for the specific address rather than using a national average. The difference between 0.6% and 1.8% on a $475,000 home is $475 a month.
Test the payment for three months
Move the difference between your current rent and the projected payment into savings each month. If that hurts, buy less house rather than hoping it gets easier.
Add maintenance to the picture
Budget 1% of the home's value a year for upkeep, so about $400 a month on a $475,000 house. It is not part of the mortgage, but it is part of owning.
Common questions
Why is my estimate different from another lender's?
Usually because of assumptions rather than rates. Check whether the other estimate includes taxes, insurance, and mortgage insurance, and whether it quotes a rate or an APR. APR includes lender costs and is the fairer comparison.
What is the difference between rate and APR?
The rate determines your monthly interest. The APR folds in points and lender fees to express the true annual cost. Two loans at 6.250% can carry very different APRs, which is precisely the point of the disclosure.
Does the calculator include HOA dues?
Add them separately. Underwriting counts HOA dues in your housing ratio, so a $340 monthly assessment reduces what you can borrow by about $53,000 of purchase price.
Should I put 20% down if I can?
It removes mortgage insurance and lowers the payment, but it also drains reserves. Many members are better served putting 10% down and keeping six months of expenses liquid, then reaching 20% equity through appreciation and payments.
When does mortgage insurance come off?
You may request cancellation at 20% equity based on the original value, and it terminates automatically at 22%. On a conventional loan, appreciation can get you there sooner with a new appraisal.
Is a pre-approval the same as this estimate?
No. This is arithmetic; a pre-approval is a decision, made after we verify income, assets, and credit. Sellers respond to the second one.
Turn the estimate into an approval
Once the number looks right, a pre-approval takes about fifteen minutes and costs nothing.