For aspiring homebuyers looking to purchase a home, higher mortgage rates can add hundreds of dollars in additional borrowing costs. But buyers of newly constructed homes enjoy lower mortgage rates because homebuilders offer lower interest rates.

In fact, some buyers of newly built homes are getting mortgage rates of less than 6 percent, John Burns, CEO of John Burns Real Estate Consulting, wrote on LinkedIn this week.

That's because most large homebuilders spend 4-6 percent of the proceeds from the sale of a home to permanently lower mortgage rates for homebuyers, Burns said.

Most large homebuilders spend 4-6 percent of their home sale proceeds on permanently lowering mortgage rates for homebuyers.

Burns explains that they can afford to do this because their profit margins have risen over the past few years, and lower lumber prices have helped reduce construction costs.

Rebating 4-6 percent to keep sales strong is a smart move for them, Burns added.

That's one of the key reasons why new home sales are higher than existing home sales. Existing-home sales hit a six-month low as few homeowners listed their homes for sale. The number of single-family homes listed in July was at a record low since the 1980s, compared to the same month in previous years.

New home sales slowed in only 12 percent of the largest U.S. markets, according to a study by Burns.

Many aspiring homeowners rely on mortgages to purchase their homes, and each rise or fall in interest rates adds or subtracts hundreds of dollars to the cost of borrowing. Interest rates can also affect a homebuyer's purchasing power.

Price reductions to purchase a home can be permanent or temporary. For example, a mortgage product such as 3-2-1 Temporary Rate Reduction offers a lower interest rate for the first few years of repayment, after which the rate is permanently reset to a higher market rate.

A 3-2-1 Temporary Rate Reduction works like this: when a seller or builder pays a certain amount up front to purchase a lower interest rate, that rate drops from the current rate of about 7% to 4% at the beginning of the payment period. After one year, the rate rises to 5 per cent, then to 6 per cent the following year, and then to 7 per cent.

Alternatively, the seller can offer a 2-1 buyout with two adjustment periods: 5 per cent at the beginning, 6 per cent a year later, and then 7 per cent or the market rate.

Typically, these rate cuts are paid for by the homebuyer, who sets aside a portion of the down payment, or the seller or homebuilder can use them as a negotiating tactic.

With 30-year rates hovering around 7.25%, a homeowner with a $3,000 monthly housing budget could only afford a $429,000 home today, Redfin said. If they had bought a home at the same time last year, they would have been able to buy a $500,000 home on the same budget with rates averaging about 5.5 percent.

These figures assume the homebuyer puts 20 percent down, uses a 30-year mortgage, pays a 1.25 percent property tax rate, a 0.5 percent homeowner's insurance rate, and has no homeowner's association fees.

Builders such as D.R. Horton and Lennar have been relying on rate buybacks to offer homebuyers lower rates on 30-year mortgages. So far, they've had success, according to updates from both companies on recent earnings calls.

Rate reductions have been an effective incentive for us, Paul Romanowski, executive vice president and chief partnership officer at D.R. Horton, said during the company's third-quarter earnings call last month.

We've been staying about a point below market, and we'll measure that against the movement of interest rates, whether up or down," he said. But we've found that it's one of our most effective incentives, and we've stuck to it."

"We can lower mortgage rates in a way that the resale market can't," Jon Jaffe, Lennar's co-CEO and president, said on the company's second-quarter earnings call in June." So if we need to accelerate the pace of sales that the market is giving us, we have leverage that we can use."