How Much Buying Power Does One Point of Interest Cost? A $100,000 Income Example

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By De Van Do -- Published October 25, 2026 -- 8 min read

Why a Small Rate Change Is a Big Deal

When people compare mortgage rates, a one point difference sounds small. It is not. A mortgage is a fixed monthly payment spread over 360 months, and the rate decides how much of that payment is eaten by interest. When rates go up, the same monthly payment supports a smaller loan.

This article measures that effect with a simple model. It uses one income, one set of debt limits, and three round interest rates so you can see the pattern. The rates 6%, 7%, and 8% are hypothetical, chosen to show the size of a one point step. They are not quotes. For real rates, Freddie Mac publishes a weekly survey: as of October 22, 2026, the average 30-year fixed rate was 7.32%, compared with 6.19% a year earlier.

The survey figure is an average for borrowers with good or excellent credit and 20 percent down. Your own rate may be higher or lower, and the survey does not report points or fees.

The Assumptions

A model is only as honest as its assumptions, so here they are in full.

Gross income is $100,000 a year, which is $8,333 a month. Other monthly debts, such as a car loan or student loan, total $500. Property tax and homeowners insurance together are assumed to be $500 a month. That figure is an assumption and not a national average. Property taxes vary widely by location, and no national figure was verified for this article. For context on insurance alone, the National Association of Insurance Commissioners reported a countrywide average premium of $1,737 a year for the common HO-3 homeowners policy in its 2023 data, published in July 2026. Premiums have risen since then and vary a lot by state.

The loan is a 30-year fixed mortgage. Mortgage insurance, HOA dues, and other housing costs are left out, so the model slightly overstates what you could borrow if those apply.

The debt-to-income ratio, or DTI, is the share of gross monthly income that goes to debt payments. The CFPB defines it as all monthly debt payments divided by gross monthly income, and notes that limits vary by loan type and lender. Two limits are used here because both appear in Fannie Mae's Selling Guide (version dated April 2, 2025): 36 percent, the maximum for manually underwritten loans, and 45 percent, which manual underwriting may reach if the borrower meets the credit score and reserve requirements. Loans approved through Fannie Mae's automated system can go up to 50 percent. Those are Fannie Mae limits for conventional loans. FHA and other programs have their own rules.

How the Model Works

The steps are simple. Multiply gross monthly income by the DTI limit to get the maximum total monthly debt. Subtract the $500 of other debt. Subtract the $500 for taxes and insurance. What is left is the most you can pay in principal and interest. Then ask what loan balance that payment can support at each rate.

At a 36 percent DTI the limit is $3,000 a month in total debt. After $500 of other debt and $500 of taxes and insurance, $2,000 is left for principal and interest.

At a 45 percent DTI the limit is $3,750. After the same subtractions, $2,750 is left.

Results at a 36 Percent Limit

With $2,000 a month available for principal and interest, the loan that fits is:

At 6%: $333,583.

At 7%: $300,615.

At 8%: $272,567.

Going from 6% to 7% cuts the loan by $32,968, or about 9.9 percent. Going from 7% to 8% cuts it by another $28,048, or about 9.3 percent. Each full point costs roughly one tenth of your borrowing power in this example.

If you put 10 percent down, those loans correspond to home prices of about $370,600 at 6%, $334,000 at 7%, and $302,900 at 8%. These prices ignore closing costs and the fact that taxes and insurance would likely rise on a more expensive home, which would lower the figures a bit.

Results at a 45 Percent Limit

With $2,750 a month available for principal and interest, the loan that fits is:

At 6%: $458,677.

At 7%: $413,346.

At 8%: $374,780.

The pattern is the same. The step from 6% to 7% removes $45,331, and the step from 7% to 8% removes $38,566. The dollar amounts are larger because the starting loan is larger, but the percentage loss is about the same.

The gap between the two limits is also instructive. Moving from the 36 percent limit to the 45 percent limit raises the loan at 7% from $300,615 to $413,346, a difference of $112,731. Being allowed a higher DTI is worth more than a full two points of rate in this example. That is also the riskiest way to buy, because a payment that takes 45 percent of gross income leaves little room after taxes and living costs.

The Same Idea Seen From the Payment Side

You can also look at it from the other direction. On a fixed $400,000 loan, the monthly principal and interest payment is $2,398.20 at 6%, $2,661.21 at 7%, and $2,935.06 at 8%. Each point adds roughly $263 to $274 a month, which is about 10 to 11 percent more than the previous step.

Now apply the real survey rates. At the 36 percent limit in this model, the loan that fits at 6.19%, the rate from a year earlier, is about $326,900. At 7.32%, the October 22, 2026 average, it is about $291,200. That is a drop of about $35,700 in borrowing power, or roughly 11 percent, from a rate change of 1.13 points. At the 45 percent limit, the same two rates give about $449,500 and $400,300, a drop of about $49,100.

These are model results, not approvals. Real approvals depend on credit scores, reserves, the loan program, and the lender's own overlays.

What Else Changes the Answer

Several things move the result by as much as a point of rate.

Down payment. A bigger down payment lowers the loan for any given price, which helps a payment fit under the limit and can avoid mortgage insurance. See our article on down payment strategies for how those trade-offs work.

Other debts. In this model, every $100 of monthly debt you remove adds $100 of room under the limit, which supports a larger loan by roughly $15,000 at 7%. Paying off a car loan can matter as much as shopping for a lower rate.

Loan type. FHA manual underwriting uses two ratios, one for the housing payment and one for total fixed payments. HUD's published limits include 31 and 43 percent with no compensating factors, 37 and 47 with one compensating factor, and 40 and 50 with two, for borrowers with a credit score of 580 or higher. Automated approvals follow different rules that are not covered here.

The type of qualified mortgage. Since a rule issued in December 2020, the General QM test for most loans no longer uses a fixed 43 percent DTI cap. It uses a price test, comparing the loan's APR to the average prime offer rate, and the lender must still consider and verify income and debts. Lenders may keep their own, stricter limits.

When This Model Is the Wrong Tool

Do not treat the maximum as the target. A qualifying number tells you what a lender may approve. It does not tell you what leaves you comfortable. Childcare, commuting, savings goals, and irregular income are invisible to a DTI calculation.

Do not assume the $500 for taxes and insurance fits your area. In some places that figure is far too low, and in others it is too high. Look up the actual tax bill for homes you are considering and get an insurance quote early.

Do not rely on the survey average as your rate. Your credit, down payment, and the lender decide it, and the only reliable number is the one on a Loan Estimate.

And do not assume that waiting for rates to fall will fix affordability. Rates may fall or rise, and home prices and competition can move too. A decision to wait is a bet either way, and the model above is better used to decide what you can afford at today's rate than to guess at tomorrow's.

Running Your Own Numbers

To use this on your own situation, write down gross monthly income, monthly debts, and an honest estimate of tax and insurance for the area you want. Choose a DTI that you would be comfortable living with, not just the highest the lender allows. Then use the mortgage calculator and change the rate in one point steps. Watching the loan size shrink as the rate rises is the fastest way to understand why a rate quote deserves as much attention as the price of the house.

Open the Mortgage Calculator

Change the rate in one point steps and watch the payment move.

Related guides

How Much House You Can Afford (I Ran the Lender Math)
On a $90,000 income the lender maximum comes to about $282,429, and it needs $43,128 in cash. I also found that the rate moves your buying power more than anything you can control.

The DTI Rule That Actually Binds (I Tested Both Ratios)
Lenders are often described as applying two DTI limits, 28% and 43%. I ran both through my own calculator and found that on a typical income the second one does nothing at all until your monthly debts pass a specific threshold.

Buying a Home in a High Interest Rate Environment: Strategy Guide
High mortgage rates change the calculus of home buying but do not eliminate the case for purchasing. Here is how to think through the decision and optimize your strategy when rates are elevated.

Sources

Facts, limits and rules on this page were checked against these primary sources on October 25, 2026.

About the author

De Van Do has a background in technology and built VisualMortgage out of curiosity about making mortgage math transparent. De Van Do is not a licensed loan officer or mortgage broker -- for advice specific to your situation, consult a licensed mortgage professional. Read more about VisualMortgage.

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