Banks are eager to lend a hand to first-time homebuyers, but that doesn’t mean you should borrow as much as they’ll loan you. Why? It’s all about the cash flow.

Older millennials in their early 30s are looking to buy homes. The median age of a first-time buyer is about 33, up from 29 in the 1970s, according to Zillow, a real estate marketplace site.

Lenders have recently introduced programs that will make it easier for creditworthy borrowers to buy a home with very little down even as they juggle other demands, like student loan repayment or starting a family.

Banks have partnered with Fannie Mae and Freddie Mac, two entities that provide financing to lenders, to make mortgages available to first-time buyers with a down payment that’s as low as 3 percent. For instance, Wells Fargo launched ” yourFirstMortgage” in late May. Similar programs are available at SunTrust and Bank of America. Quicken Loans offers a mortgage with a down payment option of just 1 percent.

The demand is there, banking industry representatives say. Fifteen percent of single-family home loans made in 2015 were to first-time buyers, according to the American Bankers Association. That figure has risen most years since 2009, when 9 percent of loans were made to new home purchasers.

At the same time, the median listing price for a home in the U.S. is $239,900, up 4.8 percent year over year, according to Zillow.

The low down-payment programs are different from past initiatives to encourage home ownership: Borrowers need to prove they have sufficient income and strong credit profiles, and banks generally are using fixed-rate mortgages instead of adjustable-rate loans.

“The documentation and verification is very different,” said David Doyle, lending product and pricing executive at Bank of America, which also runs a first-time buyer program. “The minimum credit score is 660,” he said. “It goes back to the point of demonstrating credit history and behaviors that indicate stability.”

“If there is anything the crisis should have underscored for industry participants, it’s that not all products are correct for all borrowers,” Doyle said.

Planners warn that while these first-time homeowner programs are helpful, borrowers should not overlook the true measure of home affordability: monthly cash flow.

Your debt-to-income ratio is the key metric to determine the amount you can safely borrow.

Housing costs, including principal and interest payments on your mortgage, as well as taxes and insurance, should account for no more than 28 percent of your gross monthly income. This so-called “front-end ratio” is a rule of thumb among lenders and financial planners.

Meanwhile, the monthly payment for your total debt, including credit cards and student loans, should not exceed 36 percent of your gross monthly income. This figure is known as the “back-end ratio.”

If your monthly debt payments equal as much as 43 percent of your gross monthly income, a lender may provide you with a “qualified mortgage,” a loan that doesn’t have harmful features, such as “interest only” payment periods or loan terms that are beyond 30 years.

Some banks are willing to offer mortgages to first-time borrowers who fall into that category — and, in some cases, whose debt repayments exceed 43 percent of their gross income.

Some advisors worry this high debt level may be unsustainable for borrowers.

“Putting down 3 percent is terrific in a low interest rate environment,” said Adam Kozak, a certified financial planner at KPL Financial Group in Eastchester, New York. “But how does that affect your cash flow? Can you eat?”

To keep things conservative, Kozak recommends that prospective borrowers use no more than 20 percent of their net monthly income toward servicing consumer debt, including credit cards and student loans.

Earmark 10 percent of your gross income for retirement, as well, and be sure that you have enough money for adequate life and disability insurance, Kozak said. Prospective buyers should also ensure they have enough of an emergency reserve to cover three to six months’ worth of expenses.

“Cash flow is always top of mind, just like if you were a company,” he said. Below, Kozak provides an example of a couple who are balancing manageable levels of debt and sufficient cash flow.

Don’t Prey to Temptation of Low Down-Payment Mortgage by Darla Mercado MSN Real Estate